国家自然科学基金60671001,61271100;陕西省自然科学基础研究重点项目2010JZ010;中国博士后科学基金2012T50878;陕西省自然科学基础研究项目批准号:SJ08-ZT06,2012JM8003资助的课题.* Project supported by the National Natural Science Foundation of ChinaGrant .60671001,61271100;the Key Program of the Natural Science Basic Research of Shaanxi Province, ChinaGrant 2010JZ010;the China Postdoctoral Science FoundationGrant 2012T50878;the Natural Science Basic Research of Shanxi Province, ChinaGrant . SJ08-ZT06,2012JM8003