安徽省科学与技术带头人后备人才基金项目No.2006-5.安徽省自然科学基金项日01043202;安徽省教育厅自然科学基金项目2006KJ219B资助 Supported by the Science and Technology Foundation of Wuhu City,Anhui,China2006-5;the Natural Science Foundation of Anhui,China01043202;the Natural Science Foundation of Education Department of Anhui,China2006KJ219B