国家自然科学基金项目(50707026);陕西省自然科学基础研究计划项目(2014JM7255);陕西省重点学科建设专项资金资助项目(5X1201);Project Supported by National Natural Science Foundation of China(50707026);Shaanxi Province Natural Science Basic Research Program(2014JM7255);Shaanxi Key Discipline Construction Special Funds(5X1201)