基金This work was supported by the National Natural Science Foundation of China(30470027 and 30225048)Natural Science Foundation of Yunnan Province(2005C0052Mand 2005C0011R).
基金This project was supported bythe National Natural Science Foundation of China(30225048and30470027)and the Natural Sci-ence Foundation of Yunnan Province(2005C0052Mand2005C0011R)