国家自然科学基金项目90717110、国家高技术研究发展计划863计划,2007A A10Z122和国家杰出青年科学基金项目30825030资助 Supported by the National Natural Science Foundation of China 90717110,the National High-tech Research and Development Program of China 863 Program,2007AA10Z122,and the National Science Fund of China for Distinguished Young Scholars 30825030