国家自然科学基金项目41271148;教育部人文社会科学研究基金项目08JA790111;湖南省教育厅科研项目10C1229;National Natural Science Foundation of China,No.41271148;Humanities and Social Science Research Foundation of the Ministry of Education of China,No.08JA790111;The Scientific Research Foundation of Education Department of Hunan Province,No.10C1229