基金This work is supported by the Natural Science Foundation of China (Grant No.10471159,No.10171118)NCET,Education Commission project Research Foundation of Chongqing(Grant No.KJ060818,KJ060804)
基金This research was partially supported by the National Natural Science Foundation of China (Grant No.10171118)Education Committee project Research Foundation of Chongqing (Grant No. 030801)National Natural Science Foundation of Chongqing (Grant No. 8904)