期刊文献+
共找到27,991篇文章
< 1 2 250 >
每页显示 20 50 100
Crop Yield and Soil Responses to Long-Term Fertilization on a Red Soil in Southern China 被引量:78
1
作者 ZHANG Hui-Min WANG Bo-Ren +1 位作者 XU Ming-Gang FAN Ting-Lu 《Pedosphere》 SCIE CAS CSCD 2009年第2期199-207,共9页
A 15-year fertilization experiment with different applications of inorganic N,P and K fertilizers and farmyard manure (M)was conducted to study the yield and soil responses to long-term fertilization at Qiyang,Hunan P... A 15-year fertilization experiment with different applications of inorganic N,P and K fertilizers and farmyard manure (M)was conducted to study the yield and soil responses to long-term fertilization at Qiyang,Hunan Province,China. Average grain yields of wheat and corn(1 672 and 5 111 kg ha-1,respectively)for the treatment NPKM were significantly higher than those(405 and 310 kg ha-1)of the unfertilized control and single inorganic fertilizer treatments.Compared with the corresponding initial values of the experiment,all treatments showed a yield decline of 9 to 111 kg ha-1 year-1 in wheat and 35 to 260 kg ha-1 year-1 in corn,respectively,and a significant pH decline of 0.07 to 0.12 pH year?1,except for the treatments PK and NPKM.After long-term fertilization,the soil organic C,soil available P,exchangeable Ca2+ and Mg2+and available Cu2+and Zn2+contents were higher in the treatment NPKM than in the treatments applied with inorganic fertilizer only.Compared to the treatment NPK,the treatment NPKM,where manure partially replaced inorganic N,had a positive impact on arresting the decline of soil pH.This improved grain yields of wheat and corn, suggesting that application of NPK fertilizer in combination with farmyard manure is important to maintain soil fertility and buffering capacity in red soil. 展开更多
关键词 CORN long-term fertilization red soil WHEAT yield
下载PDF
论中国经济的长期增长 被引量:52
2
作者 刘霞辉 《经济研究》 CSSCI 北大核心 2003年第5期41-47,共7页
中国经济是否能保持中长期的持续快速增长 ,本文在作者提出的经济增长模型的基础上 ,给出了肯定答案。该模型的基本结论是 ,一个经济体的长期增长进程分为加速和减速增长两个阶段 ,加速增长阶段表现为快速工业化和过去利用效率过低的农... 中国经济是否能保持中长期的持续快速增长 ,本文在作者提出的经济增长模型的基础上 ,给出了肯定答案。该模型的基本结论是 ,一个经济体的长期增长进程分为加速和减速增长两个阶段 ,加速增长阶段表现为快速工业化和过去利用效率过低的农村劳动力大规模城市化。目前的中国尚处于工业化、城市化过程中 ,即加速经济增长时期 ,而且这一过程还要维持相当长的时间。所以从中长期看 ,中国经济还会保持快速增长。 展开更多
关键词 中国 经济增长 工业化 农村劳动力 城市化 长期性
原文传递
长期血液透析对慢性肾衰竭患者肾性贫血、营养状态及炎症因子水平的影响 被引量:63
3
作者 赖冬梅 王燕涛 《标记免疫分析与临床》 CAS 2019年第7期1150-1154,共5页
目的分析长期血液透析对慢性肾衰竭(CRF)患者肾性贫血、营养状态及炎症因子水平的影响。方法选取2016年4月至2018年4月我院行血液透析治疗的CRF患者95例,依据血液透析治疗时间将其分为观察组(透析时间>4个月,n=55)、对照组(透析时间... 目的分析长期血液透析对慢性肾衰竭(CRF)患者肾性贫血、营养状态及炎症因子水平的影响。方法选取2016年4月至2018年4月我院行血液透析治疗的CRF患者95例,依据血液透析治疗时间将其分为观察组(透析时间>4个月,n=55)、对照组(透析时间在2~4个月,n=40),比较两组透析前、透析结束时肾功能[β2微球蛋白(β2-MG)、尿素(UA)、血肌酐(Cr)、肾损伤分子1(KIM-1)]、肾性贫血相关指标[铁调素、铁蛋白(SF)、促红细胞生成素(EPO)、血红蛋白(Hb)]、营养状态[总蛋白(TP)、白蛋白(Alb)、钙磷含量]、炎症因子水平[白介素-6(IL-6)、超敏C反应蛋白(hs-CRP)、肿瘤坏死因子-α(TNF-α)]。结果两组透析后血清β2-MG、UA、Cr及尿液中KIM-1水平均下降,观察组透析后各指标下降幅度小于对照组(P<0.05);透析后两组肾性贫血、营养状态指标基本改善,但观察组透析后铁调素、EPO、Alb不升反降,且观察组铁调素、SF、EPO、Hb、TP、Alb、钙含量均低于对照组,而磷含量高于对照组(P<0.05);透析后观察组血清IL-6、hs-CRP、TNF-α水平均高于对照组(P<0.05)。结论血液透析可较好改善CRF患者肾功能,纠正其肾性贫血、营养不良状态,降低炎症因子水平,但长期透析治疗可能加重肾性贫血及不良营养状态,应规范透析治疗方案,在透析期间加以监测。 展开更多
关键词 长期 血液透析 慢性肾衰竭 肾性贫血 营养状态 炎症因子
下载PDF
Effects of Long-Term Combined Application of Organic and Mineral Fertilizers on Microbial Biomass,Soil Enzyme Activities and Soil Fertility 被引量:54
4
作者 LI Juan ZHAO Bing-qiang +2 位作者 LI Xiu-ying JIANG Rui-bo So Hwat Bing 《Agricultural Sciences in China》 CAS CSCD 2008年第3期336-343,共8页
Soil health is important for the sustainable development of terrestrial ecosystem. In this paper, we studied the relationship between soil quality and soil microbial properties such as soil microbial biomass and soil ... Soil health is important for the sustainable development of terrestrial ecosystem. In this paper, we studied the relationship between soil quality and soil microbial properties such as soil microbial biomass and soil enzyme activities in order to illustrate the function of soil microbial properties as bio-indicators of soil health. In this study, microbial biomass C and N contents (Cmic & Nmic), soil enzyme activities, and soil fertility with different fertilizer regimes were carried out based on a 15-year long-term fertilizer experiment in Drab Fluvo-aquic soil in Changping County, Beijing, China. At this site, 7 different treatments were established in 1991. They were in a wheat-maize rotation receiving either no fertilizer (CK), mineral fertilizers (NPK), mineral fertilizers with wheat straw incorporated (NPKW), mineral fertilizers with incremental wheat straw incorporated (NPKW+), mineral fertilizers plus swine manure (NPKM), mineral fertilizers plus incremental swine manure (NPKM+) or mineral fertilizers with maize straw incorporated (NPKS). In different fertilization treatments Cmic changed from 96.49 to 500.12 mg kg^-1, and Nmic changed from 35.89 to 101.82 mg kg^-1. Compared with CK, the other treatments increased Cmic & Nmic, Cmic/Corg (organic C) ratios, Cmic/Nmic, urease activity, soil organic matter (SOM), soil total nitrogen (STN), and soil total phosphorus (STP). All these properties in treatment with fertilizers input NPKM+ were the highest. Meantime, long-term combined application of mineral fertilizers with organic manure or crop straw could significantly decrease the soil pH in Fluvo-aquic soil (the pH around 8.00 in this experimental soil). Some of soil microbial properties (Cmic/Nmic, urease activity) were positively correlated with soil nutrients. Cmic/Nmic was significantly correlated with SOM and STN contents. The correlation between catalase activity and soil nutrients was not significant. In addition, except of catalase act 展开更多
关键词 long-term fertilizer experiment soil microbial biomass soil enzyme activities soil fertility
下载PDF
珠江三角洲及河网形成演变的数值模拟和地貌动力学分析:距今6000-2500a 被引量:50
5
作者 吴超羽 包芸 +3 位作者 任杰 雷亚平 史合印 何志刚 《海洋学报》 CAS CSCD 北大核心 2006年第4期64-80,共17页
珠江三角洲是我国一个极其复杂的大尺度河口系统,具有独特的河网体系和河口湾.为了探讨距今6 000 a以来珠江三角洲和河网的形成演变,提出一个长周期动力形态模型(PRD-LTMM)并讨论长周期模拟方法的建模和验证思想,重建了距今6 000 a海进... 珠江三角洲是我国一个极其复杂的大尺度河口系统,具有独特的河网体系和河口湾.为了探讨距今6 000 a以来珠江三角洲和河网的形成演变,提出一个长周期动力形态模型(PRD-LTMM)并讨论长周期模拟方法的建模和验证思想,重建了距今6 000 a海进盛期的古珠江河口湾的水下地形作为模型的初始边界.在模型中考虑的驱动力和控制因素包括代表潮、河流流量、泥沙输入、海平面变化、沉积物压实率及新构造运动等.分析和计算了三角洲总沉积量、有效堆积空间和沉积速率,用于模型控制和校验.应用必要的模型约减技术,实际模拟了长周期模型.34个14C测年钻孔资料初步验证了模型的正确性,一些古文化遗迹证据可以印证模拟结果.地貌动力学分析进一步论证了计算结果的合理性,阐述了模型输出的地学意义.现阶段的研究揭示出海进盛期以来珠江三角洲的时空演进过程具有一些与已有研究成果大不相同的新的特征.提出距今6 000 a以来珠江三角洲等沉积时间线和若干沉积模式.珠江三角洲发育演变及其特征在很大程度上源自其继承性的地质地貌构造所造成的独特的古海湾构造形态及其对河流和海洋动力分布的重塑.珠江河口的“门”及其双向射流动力体系对珠江三角洲和河网主干,特别对口门的形成演变起了控制性的作用,模拟结果还表明,古珠江河口湾中散落的众多基岩岛丘边沿沉积是影响珠江三角洲长期演变的重要因素. 展开更多
关键词 动力形态模型 长周期 演变 珠江三角洲
下载PDF
Effect of Long-Term Rice Straw Return on Soil Glomalin, Carbon and Nitrogen 被引量:49
6
作者 NIE Jun ZHOU Jian-Min +2 位作者 WANG Huo-Yan CHEN Xiao-Qin DU Chang-Wen 《Pedosphere》 SCIE CAS CSCD 2007年第3期295-302,共8页
A long-term experiment was conducted to investigate how long-term fertilization and rice straw incorporation into soil affect soil glomalin, C and N. The combined application of chemical fertilizer and straw resulted ... A long-term experiment was conducted to investigate how long-term fertilization and rice straw incorporation into soil affect soil glomalin, C and N. The combined application of chemical fertilizer and straw resulted in a significant increase in both soil easily extractable glomalin (EEG) and total glomalin (TG) concentrations, as compared with application of only chemical fertilizer or no fertilizer application. The EEG and TG concentrations of the NPKS (nitrogen, phosphorus, and potassium fertilizer application + rice straw return) plot were 4.68% and 5.67% higher than those of the CK (unfertilized control) plot, and 9.87% and 6.23% higher than those of the NPK (nitrogen, phosphorus, and potassium fertilizer applied annually) plot, respectively. Application of only chemical fertilizer did not cause a statistically significant change of soil glomalin compared with no fertilizer application. The changes of soil organic C (SOC) and total N (TN) contents demonstrated a similar trend to soil glomalin in these plots. The SOC and TN contents of NPKS plot were 15.01% and 9.18% higher than those of the CK plot, and 8.85% and 14.76% higher than those of the NPK plot, respectively. Rice straw return also enhanced the contents of microbial biomass C (MBC) and microbial biomass N (MBN) in the NPKS plot by 7.76% for MBC and 31.42% for MBN compared with the CK plot, and 12.66% for MBC and 15.07% for MBN compared with the NPK plots, respectively. Application of only chemical fertilizer, however, increased MBN concentration, but decreased MBC concentration in soil. 展开更多
关键词 C GLOMALIN long-term fertilizer experiment N rice straw return
下载PDF
The Long-term Variation of Extreme Heavy Precipitation and Its Link to Urbanization Effects in Shanghai during 1916–2014 被引量:44
7
作者 Ping LIANG Yihui DING 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2017年第3期321-334,共14页
Using the hourly precipitation records of meteorological stations in Shanghai, covering a period of almost a century (1916-2014), the long-term variation of extreme heavy precipitation in Shanghai on multiple spatia... Using the hourly precipitation records of meteorological stations in Shanghai, covering a period of almost a century (1916-2014), the long-term variation of extreme heavy precipitation in Shanghai on multiple spatial and temporal scales is analyzed, and the effects of urbanization on hourly rainstorms studied. Results show that: (1) Over the last century, extreme hourly precipitation events enhanced significantly. During the recent urbanization period from 1981 to 2014, the frequency of heavy precipitation increased significantly, with a distinct localized and abrupt characteristic. (2) The spatial distribution of long-term trends for the occurrence frequency and total precipitation intensity of hourly heavy precipitation in Shanghai shows a distinct urban rain-island feature; namely, heavy precipitation was increasingly focused in urban and suburban areas. Attribution analysis shows that urbanization in Shanghai contributed greatly to the increase in both frequency and intensity of heavy rainfall events in the city, thus leading to an increasing total precipitation amount of heavy rainfall events. In addition, the diurnal variation of rainfall intensity also shows distinctive urban-rural differences, especially during late afternoon and early nighttime in the city area. (3) Regional warming, with subsequent enhancement of water vapor content, convergence of moisture flux and atmospheric instability, provided favorable physical backgrounds for the formation of extreme precipitation. This accounts for the consistent increase in hourly heavy precipitation over the whole Shanghai area during recent times. 展开更多
关键词 hourly precipitation long-term trend URBANIZATION extreme events
下载PDF
国外医养结合养老模式及其对中国的启示 被引量:45
8
作者 包世荣 唐魁玉 《哈尔滨工业大学学报(社会科学版)》 CSSCI 北大核心 2018年第2期58-63,共6页
2016年中国提出大力发展健康产业,同时提出健康中国2030规划。2017年,习近平总书记在中共十九大报告中强调要推动养老向多元化、多样化的方向发展,同时要加速发展医养结合养老产业。中国目前医养结合养老模式的发展相对于率先进入人口... 2016年中国提出大力发展健康产业,同时提出健康中国2030规划。2017年,习近平总书记在中共十九大报告中强调要推动养老向多元化、多样化的方向发展,同时要加速发展医养结合养老产业。中国目前医养结合养老模式的发展相对于率先进入人口老龄化阶段的发达国家是滞后的。国外有四种典型的医养结合养老产业发展模式,分别是美国的商业养老模式、日本的转型医养结合养老模式、欧洲的以英国为代表的税收筹资体制模式,以及欧洲以德国为代表的社会保险体制模式。国外医养结合养老模式对中国的启示是:应从中国医疗保障到医养结合疾病预防转变上,从完善长期照护制度上,从创新模式上,从提高医疗服务能力上以及从政策的整合和整体规划上,最终形成慢病管理、疾病预防、疾病治疗、长期照护、老年娱乐及老年再就业六位一体的医养结合养老模式。 展开更多
关键词 健康中国 医养结合 养老模式 长期照护
下载PDF
Effects of Long-Term Winter Planted Green Manure on Physical Properties of Reddish Paddy Soil Under a Double-Rice Cropping System 被引量:42
9
作者 YANG Zeng-ping XU Ming-gang +4 位作者 ZHENG Sheng-xian NIE Jun GAO Ju-sheng LIAO Yu-lin XIE Jian 《Journal of Integrative Agriculture》 SCIE CAS CSCD 2012年第4期655-664,共10页
Soil physical properties are important indicators of the potential for agricultural production.Our objective was to evaluate the effects of long-term inputs of green manures on physical properties of a reddish paddy s... Soil physical properties are important indicators of the potential for agricultural production.Our objective was to evaluate the effects of long-term inputs of green manures on physical properties of a reddish paddy soil(Fe-Typic Hapli-Stagnic Anthrosols) under a double cropping system.The common cropping pattern before the study was early-late rice-fallow(winter).The field treatments included rice-rice-fallow(R-R-WF),rice-rice-rape(R-R-RP),rice-rice-Chinese milk vetch(RR-MV),and rice-rice-ryegrass(R-R-RG).The rape,Chinese milk vetch and ryegrass were all incorporated as green manures 15 d before early rice transplanting during the following year.The soil bulk density in all green manure treatments was significantly reduced compared with the winter fallow treatment.Soil porosity with green manure applications was significantly higher than that under the winter fallow.The green manure treatments had higher 0.25-5 mm water stable aggregates and aggregates stabilities in the plow layer(0-15 cm depth) compared with the fallow treatment.The mean weight diameter(MWD) and normalized mean weight diameter(NMWD) of aggregates in the green manure treatment were larger than that with the winter fallow.Soil given green manure retained both a higher water holding capacity in the plow layer soil,and a larger volume of moisture at all matric potentials(-10,-33 and-100 kPa).We conclude that the management of double-rice fields in southern central China should be encouraged to use green manures along with chemical fertilizers to increase SOC content,improve soil physical properties and soil fertility. 展开更多
关键词 long-term experiment soil physical property green manure reddish paddy soil
下载PDF
垂直流人工湿地不同填料长期运行效果研究 被引量:40
10
作者 武俊梅 王荣 +3 位作者 徐栋 张翔凌 贺锋 吴振斌 《中国环境科学》 EI CAS CSCD 北大核心 2010年第5期633-638,共6页
在高水力负荷(2400~3400mm/d)条件下,以沸石、无烟煤、页岩、蛭石、陶瓷滤料、砾石、钢渣和生物陶粒为填料,进行垂直流人工湿地模拟柱净化污水实验(历时25个月).结果表明,随着系统的运行,各填料对COD的去除能力均有不同程度提高.沸石... 在高水力负荷(2400~3400mm/d)条件下,以沸石、无烟煤、页岩、蛭石、陶瓷滤料、砾石、钢渣和生物陶粒为填料,进行垂直流人工湿地模拟柱净化污水实验(历时25个月).结果表明,随着系统的运行,各填料对COD的去除能力均有不同程度提高.沸石对污水中氮素的处理能力保持在较高的水平,对TN和NH4+-N的平均去除率分别高达82.03%和91.32%.钢渣对TP和可溶性反应磷(SRP)的平均去除率分别高达89.61%和96.77%,且净化效果稳定;无烟煤第2阶段对磷素的净化能力低于钢渣,之后与钢渣无显著性差异.在垂直流人工湿地中,针对水质特性选择长期高效的填料,如沸石、无烟煤和生物陶粒,在高水力负荷条件下可获得更好的处理效果. 展开更多
关键词 人工湿地 水力负荷 填料 去除效率 长期运行
下载PDF
Crop Yield and Soil Properties in the First 3 Years After Biochar Application to a Calcareous Soil 被引量:40
11
作者 LIANG Feng LI Gui-tong +1 位作者 LIN Qi-mei ZHAO Xiao-rong 《Journal of Integrative Agriculture》 SCIE CAS CSCD 2014年第3期525-532,共8页
It remains unclear whether biochar applications to calcareous soils can improve soil fertility and crop yield. A long-term field experiment was established in 2009 so as to determine the effect of biochar on crop yiel... It remains unclear whether biochar applications to calcareous soils can improve soil fertility and crop yield. A long-term field experiment was established in 2009 so as to determine the effect of biochar on crop yield and soil properties in a calcareous soil. Five treatments were: 1) straw incorporation; 2) straw incorporation with inorganic fertilizer; 3), 4) and 5) straw incorporation with inorganic fertilizer, and biochar at 30, 60, and 90 t ha-l, respectively. The annual yield of either winter wheat or summer maize was not increased significantly following biochar application, whereas the cumulative yield over the first 4 growing seasons was significantly increased. Soil pH, measured in situ, was increased by a maximum of 0.35 units after 2 yr following biochar application. After 3 yr, soil bulk density significantly decreased while soil water holding capacity increased with adding biochar of 90 t ha^-1. Alkaline hydrolysable N decreased but exchangeable K increased due to biochar addition. Olsen-P did not change compared to the treatment without biochar. The results suggested that biochar could be used in calcareous soils without yield loss or significant impacts on nutrient availability. 展开更多
关键词 BIOCHAR calcareous soil crop yield soil pH long-term effect
下载PDF
Long-term changes in the fishery ecosystem structure of Laizhou Bay,China 被引量:39
12
作者 JIN XianShi SHAN XiuJuan +3 位作者 LI XianSen WANG Jun CUI Yi ZUO Tao 《Science China Earth Sciences》 SCIE EI CAS 2013年第3期366-374,共9页
Laizhou Bay provides a critical spawning and nursery habitat for many fishery species, including commercially important spe- cies, such as Fenneropenaeus chinensis and Larimichthys polyactis. The bay is severely stres... Laizhou Bay provides a critical spawning and nursery habitat for many fishery species, including commercially important spe- cies, such as Fenneropenaeus chinensis and Larimichthys polyactis. The bay is severely stressed due to high fishing pressure and environmental changes. Based on the long-term ecosystem surveys in Laizhou Bay during the main spawning period (May) of most fishery species from 1959 to 2008, the responses of the Laizhou Bay fishery ecosystem were analyzed here, including regime shifts in species composition, biomass, species diversity, zooplankton, phytoplankton, and environmental variables. The dominant species of large-size and high economic value (e.g. Trichiurus haumela, L. polyactis) have been replaced by the short-lived, low-trophic-level planktivorous pelagic species (e.g. Setipinna taty, Engraulisjaponicus) since the 1980s, and it is probable that the small-sized pelagic fishes have been recently replaced by invertebrates (e.g. Oratosquilla oratoria, Crangon affinis). The biomass of fishery resources declined continuously from 423.6 kg haul 1 h-1 in 1959 to 164.6 kg haul-l h i in 1982, 37.7 kg haul-1 h-1 in 1993, and less than 8 kg haul 1 h-a in 1998-2008. Moreover, the biomass of zooplankton showed an increasing trend during 1959-2006, but showed a slight decline in 2008. The abundance of phytoplankton increased from 1959 through 1982, decreased substantially in 1993, and increased again until 2004. More recently, however, the phytoplankton abundance was very low. The sea surface temperature (SST) and sea bottom temperature (SBT) in May increased by 0.23~C a-~ and 0.16~C a-~, respectively, during 1982-2008. The salinity in May showed large fluctuations and reached its lowest val- ues in 2004 and 2006. The ratio of dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphate (DIP) increased. However, the dissolved silicon (DSi):DIP and DSi:DIN ratios decreased to a low level during 1959-2008. These changes seri- ously impacted primary produ 展开更多
关键词 long-term changes fishery ecosystem multi-stress Laizhou Bay
原文传递
Chronic complications of spinal cord injury 被引量:37
13
作者 Nebahat Sezer Selami Akkus Fatma Gülcin Ugurlu 《World Journal of Orthopedics》 2015年第1期24-33,共10页
Spinal cord injury(SCI) is a serious medical condition that causes functional, psychological and socioeconomic disorder. Therefore, patients with SCI experience significant impairments in various aspects of their life... Spinal cord injury(SCI) is a serious medical condition that causes functional, psychological and socioeconomic disorder. Therefore, patients with SCI experience significant impairments in various aspects of their life. The goals of rehabilitation and other treatment approaches in SCI are to improve functional level, decrease secondary morbidity and enhance health-relatedquality of life. Acute and long-term secondary medical complications are common in patients with SCI. However, chronic complications especially further negatively impact on patients' functional independence and quality of life. Therefore, prevention, early diagnosis and treatment of chronic secondary complications in patients with SCI is critical for limiting these complications, improving survival, community participation and health-related quality of life. The management of secondary chronic complications of SCI is also important for SCI specialists, families and caregivers as well as patients. In this paper, we review data about common secondary longterm complications after SCI, including respiratory complications, cardiovascular complications, urinary and bowel complications, spasticity, pain syndromes, pressure ulcers, osteoporosis and bone fractures. The purpose of this review is to provide an overview of risk factors, signs, symptoms, prevention and treatment approaches for secondary long-term complications in patients with SCI. 展开更多
关键词 Spinal cord injury Chronic complications Management of complications long-term morbidity Secondary morbidity of spinal cord injury
下载PDF
长期施肥对紫色土酶活的影响 被引量:28
14
作者 熊明彪 雷孝章 +2 位作者 田应兵 宋光煜 曹叔尤 《四川大学学报(工程科学版)》 EI CAS CSCD 2003年第4期60-63,99,共5页
研究了长期施有机肥、化学氮磷钾肥及有机无机肥配施对紫色土酶活的影响。结果表明,长期不同施肥紫色土土壤酶活发生了显著变化。长期有机肥与化学NPK肥配施有利于紫色土酶活的改善。土壤有机质含量与土壤脲酶(URE)酶活、过氧化氢酶(CAT... 研究了长期施有机肥、化学氮磷钾肥及有机无机肥配施对紫色土酶活的影响。结果表明,长期不同施肥紫色土土壤酶活发生了显著变化。长期有机肥与化学NPK肥配施有利于紫色土酶活的改善。土壤有机质含量与土壤脲酶(URE)酶活、过氧化氢酶(CAT)酶活呈极显著正相关(r>0.661,p<0.01,n=14),说明土壤有机质含量是影响土壤CAT、URE酶活高低的重要因素。土壤中URE、CAT、中性磷酸酶(NEP)之间存在相互刺激作用,CAT酶活与多酚氧化酶(PPO)酶活之间存在此消彼长的关系。 展开更多
关键词 土壤酶活 长期施肥 紫色土
下载PDF
Phosphorus Changes and Sorption Characteristics in a Calcareous Soil Under Long-Term Fertilization 被引量:36
15
作者 GUO Sheng-Li DANG Ting-Hui HAO Ming-De 《Pedosphere》 SCIE CAS CSCD 2008年第2期248-256,共9页
Knowledge of phosphorus (P) behavior in long-term fertilized soils is essential for programming fertilization practices and for sustaining environmental quality. The long-term (1984-1997) effects of various fertil... Knowledge of phosphorus (P) behavior in long-term fertilized soils is essential for programming fertilization practices and for sustaining environmental quality. The long-term (1984-1997) effects of various fertilization treatments on P changes and sorption isotherms as well as the relationship of soil properties to P sorption and P forms were evaluated in an Ustic Isohumisol, a calcareous soil, on the Loess Plateau, China. Compared to 1984, after 13 years of crop production, total soil P in the no-P treatments (control and N treatment) decreased by 5%-7%, but in the phosphorus fertilizer alone (P), nitrogen and phosphorus fertilizers in combination (NP), manure alone (M), and nitrogen and phosphorus fertilizers and manure in combination (NPM) treatments, it increased by 22%, 19%, 28%, and 58%, respectively. Residual fertilizer P was found mainly in NH4Ac-soluble P (Cas-P), followed by NaHCO3-soluble P (NaHCO3-P), and NH4F-soluble P (Al-P). Phosphorus sorption in the soils with different fertilization practices fit the Langmuir equations. Phosphorus sorption capacity in the no-P treatments increased, whereas it decreased in the P-included treatments (P, NP, and NPM treatments). Phosphorus sorption maximum (Qm) was significantly and negatively correlated to inorganic P including NaHCO3-P, Cas-P, NaOH-Na2CO3-soluble P (Fe-P), and Al-P (P ≤ 0.01). Moreover, long-term fertilization increased soil organic carbon in the NP, M, and NPM treatments and decreased pH in the NP and NPM treatments. Thus, the ability of the soil to release sorbed P to the environment increased under long-term P fertilization. 展开更多
关键词 calcareous soil long-term fertilization P accumulation P sorption P transformations
下载PDF
2006~2015年北京市不同地区O_3浓度变化 被引量:36
16
作者 王占山 李云婷 +4 位作者 安欣欣 李倩 孙乃迪 王步英 潘锦秀 《环境科学》 EI CAS CSCD 北大核心 2018年第1期1-8,共8页
对2006~2015年北京市定陵、官园、琉璃河和前门这4个站点的O_3连续监测数据进行分析,探讨其浓度水平、变化趋势、时间变化规律以及和前体物、气象要素的关系.结果表明,定陵站十年平均浓度水平最高(65.2μg·m^(-3)),其次为琉璃河(5... 对2006~2015年北京市定陵、官园、琉璃河和前门这4个站点的O_3连续监测数据进行分析,探讨其浓度水平、变化趋势、时间变化规律以及和前体物、气象要素的关系.结果表明,定陵站十年平均浓度水平最高(65.2μg·m^(-3)),其次为琉璃河(53.4μg·m^(-3))、官园(49.6μg·m^(-3))和前门(40.4μg·m^(-3)).定陵O_3浓度呈下降趋势[0.5μg·(m^3·a)^(-1)],而官园[0.9μg·(m^3·a)^(-1)]、琉璃河[0.3μg·(m^3·a)^(-1)]和前门[0.3μg·(m^3·a)^(-1)]均呈上升趋势.从月变化来看,各站点O_3浓度最高值均出现在6~8月,出现频次最高的为7月(17次),平均月均浓度为99.8μg·m^(-3);最低值均出现在11、12月和1、2月,出现频次最高的为1月(14次),平均月均浓度为16.6μg·m^(-3).从日变化来看,近年来O_3浓度峰值出现的时间明显提前,近3年峰值均在15:00~16:00出现,提前了1~2 h.2015年定陵站O_3重污染天数达到11 d,比2013年增加了10 d,表明近年来夏季北京下风向山区的O_3重污染状况愈发严重.与前体物的相关性分析表明,定陵站O_3浓度与NO2浓度呈正相关,其余站点两者浓度均呈负相关,暗示定陵站O_3生成的前体物控制区可能为NO2控制区,而其他站点为VOCs控制区.与气象要素的相关性分析表明,O_3浓度与温度呈正相关关系,与湿度和气压呈负相关关系,温度对O_3浓度的影响最大,其次是气压和湿度.当日最高温度超过30℃,相对湿度介于30%至70%之间时,北京市O_3日最大8 h滑动平均浓度超过200μg·m^(-3)的概率较高,空气质量级别会达到轻度至中度污染的级别. 展开更多
关键词 北京 O3 长期 前体物 气象条件 控制区
原文传递
Long-term follow-up of the effects of fecal microbiota transplantation in combination with soluble dietary fiber as a therapeutic regimen in slow transit constipation 被引量:35
17
作者 Xueying Zhang Hongliang Tian +6 位作者 Lili Gu Yongzhan Nie Chao Ding Xiaolong Ge Bo Yang Jianfeng Gong Ning Li 《Science China(Life Sciences)》 SCIE CAS CSCD 2018年第7期779-786,共8页
As some studies have reported that strategies targeting the gut microbiota such as fecal microbiota transplantation(FMT) with or without other microecological therapy might have efficacy in treating slow transit const... As some studies have reported that strategies targeting the gut microbiota such as fecal microbiota transplantation(FMT) with or without other microecological therapy might have efficacy in treating slow transit constipation(STC), we conducted a singlecenter, open-label trial to study the long-term effect of FMT combined with soluble dietary fiber(pectin) on STC. Thirty-one adult patients with STC were enrolled into the trial. Patients received 6-day FMT procedures repeatedly for the first 3 months and soluble dietary fiber(pectin) daily during the follow-up. The rate of clinical remission and improvement, stool consistency, the Wexner constipation scale, and assessment of constipation-related symptoms were evaluated at week 4 and 1 year later. The clinical remission and improvement rates at week 4 were 69.0%(20/29) and 75.9%(22/29), respectively. At the end of the study,48.3%(14/29) of patients continued to have at least three complete spontaneous bowel movements per week and 58.6%(17/29)of patients showed clinical improvements. Stool consistency, the Wexner constipation scale, and constipation symptoms improved both at short-term and long-term follow-up. The results indicated that FMT in combination with soluble dietary fiber(pectin) had both short-term and long-term efficacy in treating STC. 展开更多
关键词 fecal microbiota transplantation soluble dietary fiber slow transit constipation long-term efficacy
原文传递
中国山区发展研究的态势与主要研究任务 被引量:33
18
作者 陈国阶 《山地学报》 CSCD 北大核心 2006年第5期531-538,共8页
山区发展问题是一个世界性难题。山区发展滞后是全球普遍的现象。国际上对山区发展研究十分重视,但发达国家与发展中国家因山区发展的水平和方向不同,对其研究的内容也明显差异。我国山区发展既不同于一般发展中国家,也有别于发达国家,... 山区发展问题是一个世界性难题。山区发展滞后是全球普遍的现象。国际上对山区发展研究十分重视,但发达国家与发展中国家因山区发展的水平和方向不同,对其研究的内容也明显差异。我国山区发展既不同于一般发展中国家,也有别于发达国家,正处于受全国工业化、城镇化快速发展冲击的变革期。山区发展在全国总体战略中占有重要地位,但当前是全国区域发展不平衡的主要贡献者,是“三农”问题的集中区和难点区,是全国脱贫的最后攻坚区。国内对山区发展研究虽然已取得巨大进展,但仍不适应新时期对山区发展的需求,加强全国山区发展研究势在必行。当前我国山区发展研究的重点应放在:山区发展战略,建设社会主义新山区,山区工业化,山区农业产业化,山区聚落和山区脱贫等方面上。应以科学发展观统帅山区发展研究,引入现代发展新理念,引进现代科学新理论和新方法,分别在国家层次、区域层次和聚落层次上开展研究;提倡深入山区,深入农村,深入农户;创建山区发展的长期、连续、定点的跟踪调查、监测,构建全国山区发展社会观测网络。 展开更多
关键词 山区发展 社会主义新山区 山区工业化 山区聚落 长期跟踪监测
下载PDF
农地产权、要素配置与农户投资激励:“短期化”抑或“长期化”? 被引量:34
19
作者 胡雯 张锦华 陈昭玖 《财经研究》 CSSCI 北大核心 2020年第2期111-128,共18页
文章基于粮食作物、经济作物和水稻三类生产特性,利用我国9省(区)2704个农户的调查数据,实证考察了农地产权和要素配置对农户投资激励的因果效应。研究表明:(1)农地产权对农户投资激励的作用存在历史动态的过程、个体差异的效果和各项... 文章基于粮食作物、经济作物和水稻三类生产特性,利用我国9省(区)2704个农户的调查数据,实证考察了农地产权和要素配置对农户投资激励的因果效应。研究表明:(1)农地产权对农户投资激励的作用存在历史动态的过程、个体差异的效果和各项政策的交互,并且表现为短期化和长期化的特征;(2)农地产权不直接作用于农户投资决策,而是通过农地流转的配置行为间接激励短期化(服务外包)和长期化(自购机械)的投资行为;(3)产权稳定改善了农户配置农地要素的灵活性,转入农地的农户更倾向于长期化投资,转出农地的农户短期化投入更显著;(4)农地确权促进水稻种植户的长期投资行为,抑制稻农的短期化投资。文章认为,农地产权制度要保持产权的灵活性和强度,通过放松产权管制来盘活经营权和激活生产要素流动,由此提高要素配置效率和农业生产绩效。重新审视农户异质性的多目标函数和要素禀赋的约束条件,才是农户依据价格信号和政策导向决策投资的题中之义。 展开更多
关键词 农地产权 要素配置 投资激励 短期化 长期化
原文传递
用学术影响力评价学术论文——兼论关于学术传承效应和长期引用的两个新指标 被引量:33
20
作者 尚海茹 冯长根 孙良 《科学通报》 EI CAS CSCD 北大核心 2016年第26期2853-2860,共8页
1引言 学术论文是科学技术研究,特别是自然科学基础研究成果的重要表现形式,对其学术影响力的研究一直被科技界所关注.研究学术影响力的一个重要方面是后续学术论文与之前发表的学术论文具有什么关系,这种研究对于学术创新具有重大意义.
关键词 SCIENTIFIC research ACADEMIC influence long-term CITATION ACADEMIC INHERITANCE ACADEMIC chain
原文传递
上一页 1 2 250 下一页 到第
使用帮助 返回顶部