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精细农业中最佳土壤采样间距确定方法的研究 被引量:10
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作者 任振辉 吴宝忠 《农机化研究》 北大核心 2006年第6期82-85,共4页
土壤肥力是土壤供应和协调植物生长发育所需要的水分、养分、空气和热量的能力。其随着自然环境条件变化以及农业生产活动的影响不断地产生变化,因此及时采样分析土壤肥力的动态变化,使其与作物需求处于协调状态,有利于作物的稳产、高... 土壤肥力是土壤供应和协调植物生长发育所需要的水分、养分、空气和热量的能力。其随着自然环境条件变化以及农业生产活动的影响不断地产生变化,因此及时采样分析土壤肥力的动态变化,使其与作物需求处于协调状态,有利于作物的稳产、高产。通过对试验田土壤密集采样,测定其N、P、K、OM等成分的含量,利用经典的数理统计、地学统计及分形理论与方法,对数据变化规律进行分析,最终确定出能够保证以足够精度反映出土壤肥力分布空间差异性的最大采样间距。 展开更多
关键词 土壤学 土壤采样 理论研究 分形 地学统计 精细农业 空间差异
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理论进化与生物进化的类比 被引量:1
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作者 王景荣 胡静波 《辽阳石油化工高等专科学校学报》 1999年第2期68-71,共4页
理论进化与生物进化有许多相似之处.生物进化遵循“生物变异、自然选择、适应环境”的规律.理论进化也遵循“理论变异、社会选择、理论适应”的规律.因此,坚持党的“百花齐放”、“百家争鸣”方针,有利于科学理论的创新和进步.
关键词 理论 社会选择 理论适应 类比 进化规律 生物进化
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Have some landscapes in the eastern Canadian boreal forest moved beyond their natural range of variability?
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作者 Pierre Grondin Sylvie Gauthier +3 位作者 Veronique Poirier Patrice Tardif Yan Boucher Yves Bergeron 《Forest Ecosystems》 SCIE CSCD 2018年第4期412-428,共17页
Background: In the contxt of ecosystem management, the present study aims to compare the natural and the present-day forested landscapes of a large territory in Quebec(Canada). Using contemporary and long-term fire cy... Background: In the contxt of ecosystem management, the present study aims to compare the natural and the present-day forested landscapes of a large territory in Quebec(Canada). Using contemporary and long-term fire cycles, each natural forst landscape is defined according to the variability of its structure and composition, and compared to the present-day landscape. This analysis was conducted to address the question of whether human activities have moved these ecosystems outside the range of natural landscape variability.Methods: The study encompassed a forested area of 175 000 km2 divided into 14 landscapes. Using a framework that integrates fire cycles, age structure and forest dynamics, we characterized the forest composition and age structures that resulted from three historical fire cycles(110,140, and 180 years) representative of the boreal forest of eastern Canada. The modeled natural landscapes were compared with present-day landscapes in regard to the proportion of old-growth forests(landscape level) and the proportion of late-successional forest stands(landscape level and potential vegetation type).Results: Four landscapes(39%) remain within their natural range of variability. In contrast, nine landscapes(54%)show a large gap between natural and present-day landscapes. These nine are located in the southern portion of the study area, and are mainly associated with Abies-Betula vegetation where human activities have contributed to a strong increase in the proportion of Populus tremuloides stands(early-successional stages) and a decrease of oldgrowth forest stands(more than 100 years old). A single landscape(7%), substantially changed from its potential natural state, is a candidate for adaptive-based management.Conclusion: Comparison of corresponding natural(reference conditions) and present-day landscapes showed that ten landscapes reflecting an important shift in forest composition and age structure could be considered beyond the range of their natural variability. The description of a landscape's nat 展开更多
关键词 Ecosystem management Reference conditions Natural variability RESILIENCE Fire cycle Age structure Forest dynamics Potential vegetation type Landscape ecology theoretical natural landscape Present-day landscape
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女性主义文论在中国的发展
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作者 禹建湘 《吉首大学学报(社会科学版)》 2004年第1期71-77,共7页
经过20多年的探索,中国女性主义文论已基本建构完成,但也存在一些理论盲点或不完善之处,在新的历史条件下,一些学者以一种多视角的姿态,开辟了新的女性主义文论研究领域。
关键词 女性主义文论 理论建构 本土化 盲点 嬗变
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