国家自然科学基金项目41401602;陕西省自然科学基础研究计划资助项目2014JQ2-4021;陕西省重点科技创新团队计划项目2014KCT-27;西北大学研究生自主创新项目YZZ15011 [National Natural Science Foundation of China,No.41401602;The Project Supported by Natural Science Basic Research Plan in Shaanxi Province of China,No.2014JQ2-4021;Key Scientific and Technological Innovation Team Plan of Shaanxi Province,No.2014KCT-27;Graduate Student Innovation Project of Northwest University,No.YZZ15011]