广西卫生厅重点项目No.2010074;广西自然科学基金资助项目No.2012GXNSFAA053134;广西研究生教育创新计划项目资助No.YCSZ2012045.Project supported by Key Projects of Guangxi Health BureauNo.2010074,the Natural Science Foundation of Guangxi ProvinceNo.2012GXNSFAA053134,and the Innovation Project of Guangxi Postgraduate Education FundNo.YCSZ2012045