国家自然科学基金项目31271723,31201210;四川省杰出青年基金项目2011JQ0016;四川省教育厅科研项目14ZA0012资助。 This study was supported by the National Natural Science Foundation of China31271723,31201210;Sichuan Provincial Youth Fund2011JQ0016;the Scientific Research Foundation of the Education Department of Sichuan Province14ZA0012