国家自然科学基金21666039;陕西省科技项目2013K11-08,2013SZS20-P01,2015YG174;陕西省教育厅科研基金项目15JS119;延安大学专项基金2013YDZ-07;延安大学研究生教育创新项目No.YCX201602the National Natural Science Foundation of China21666039;the Science and Technology Project of Shaanxi Province2013K11-08,2013SZS20-P01,2015YG174;the Science Research Fund of Shaanxi Provincial Education Department15JS119;the Yan'an University Special Fund2013YDZ-07;the Yan'an University Graduate Education Innovation ProjectYCX201602