本文由青海省科技厅自然科学基金项目2011-Z-903、青海师范大学创新基金项目QS2012-08、青海省重点实验室发展专项2014-Z-Y24,2015-Z-Y01资助;This work was supported by the Natural Science Foundation from Science and Technology Department of Qinghai Province,China 2011-Z-903,the Innovation Foundation of Qinghai Normal University QS2012-08 and the Key Laboratory Development Projects of Qinghai Province,China 2014-Z-Y24,2015-Z-Y01.