国家自然科学基金资助项目81270102;重庆市自然科学基金资助项目cstc2012jjA10050;重庆市教委科学技术研究项目No.KJ120301Supported by the National Natural Science Foundation of China81270102;Chongqing Natural Science Foundationcstc2012jjA10050;the Scientific and Technological Research Program of Chongqing Municipal Education CommissionKJ120301