基金Supported by the National Natural Science Foundation of China under Grant Nos.60373066, 60425206, 90412003 (国家自然科学基金)the National Basic Research Program of China under Grant No.2002CB312000 (国家重点基础研究发展计划(973))the Jiangsu High-Tech Research Project of China under Grant No.20020286004 (高等学校博士学科点专项科研基金)