国家自然科学基金资助项目30770466;四川省教育厅资助项目2006A113;四川省科技厅资助项目05JY029-107;四川省重点学科建设资助项目SZD0420Supported by the National Natural Science Foundation of China30670209;the Education Department Foundation of Sichuan,China2006A113;the Department of Science and Technology of Sichuan,China05JY029-107;the Key Construction Discipline of Sichuan,ChinaSZD0420