国家自然科学基金61175004;北京市自然科学基金4112009;北京市教委科技发展重点项目KZ201210005007;高等学校博士学科点专项科研基金20121103110029资助@@@@Supported by National Natural Science Foundation of China61175004;Natural Science Foundation of Beijing4112009;Beijing Municipal Education Commission Science and Technol-ogy Development Plan Key ProjectKZ201210005007;Spe-cialized Research Fund for the Doctoral Program of Higher Ed-ucation20121103110029