作者机构:[1]College of Mathematics and Information Science, Shaanxi Normal University, Shaanxi 710062, P. R. China, [2]College of Science, Hebei University of Science and Technology, Hebei 050018, P. R. China, [3]School of Mathematics and Science, Shijiazhuang University of Economics, Hebei 050031, P. R. China
相关基金:Supported by National Natural Science Foundation of China (Grant No.10926055); the Foundation of Hebei Province (Grant Nos. A2010000826; Z2010297); Foundation of Shijiazhuang University of Economics (GrantNo. XN201003)