1- Teaching Department of Science, Gansu University of Chinese Medicine, Dingxi, Gansu 743000
2- College of Mathematics and Information Science, Northwest Normal University, Lanzhou 730070
The National Natural Science Foundation of China (10771171); the 555 Innovation Talent Project of Gansu Province (GS-555-CXRC); the Technique Innovation Project of Northwest Normal University (NWNU-KJCXGC-212).