国家自然科学基金资助项目81301041,81371348;中央高校基本科研业务费专项资金资助项目xjj201122;陕西省教育厅科研基金资助项目2013JK0756;the National Natural Science Foundation of China81301041,81371348;the Fundamental Research Funds for the Central Universitiesxjj201122;Research Project of the Department of Education of Shaanxi Province2013JK0756