基金项目: | Supported by the National Natural Science Foundation of China (No. 10962004), Tianyuan Fund for Mathematics (No. 11126307), the National Natural Science Foundation of Inner Mongolia (No. 2011MS0104, 2012MS0105), the Research Program of Science at Universities of Inner Mongolia Autonomous Region (No. NJZZ11011) and Program of Higher-level Talents of Inner Mongolia University (No. Z20[00116). |