国家自然科学基金项目北京市卫生系统215高层次人才项目,北京市百千万人才工程创新研发类项目和2014年首都卫生发展科研专项项目(编号:2014-2-1131)资助[Supported by the National Natual Science Foundation of Chinathe Advanced Personnel Training Program (215) of Beijing Municipal Health Bureau to XLC , the Innovation Pro-ject of Beijing Municipal Human Resources and Social Secutity Bureau, and the Capital Health Research and Development of Special (No. 2014-2-1131)]