国家自然科学基金项目51271054,51071041和51231002,高等学校博士学科点专项科研基金博导类项目20110042110017及中央高校基本科研业务费项目N110105001和N120505001资助;National Natural Science Foundation of China.51271054,51071041 and 51231002;Specialized Research Fund for the Doctoral Program of Higher Education of China20110042110017;Fundamental Research Funds for the Central Universities of China.N110105001 and N120505001