基金This work was supported by the Natural Science Foundation of Jiangsu Province(No.04KJA180110),Social Development Foundation of Nantong(No.S40057,S5040),the National Natural Science Foundation of China(No. 30370462),the NSFC-RGC Joint Research Scheme of the National Natural Science Foundation of China(No.30318004)and RFDP of the State Educational Ministry of China(No. 20050284025).