国家自然科学基金No.41361106,41661115;教育部新世纪优秀人才支持计划No.NCET-11-0910;甘肃省高校基本科研业务费项目 Supported by the National Natural Science Foundation of ChinaNo.41361106,41661115,the Program for New Century Excellent Talents in University No.NCET-11-0910 and the Basic Scientific Research Business Expenses Fund Project in Gansu Province