摘要
Received 12 December 2012 Received in revised form 7 January 2013 Accepted 9 January 2013 Available online 8 February 2013
Received 12 December 2012 Received in revised form 7 January 2013 Accepted 9 January 2013 Available online 8 February 2013
基金
supported in part by the Project of Natural Science Foundation of China(Nos.21175039 and 21190044)
Research Fund for the Doctoral Program of Higher Education of China(No.20110161110016)
project supported by Hunan Provincial Natural Science Foundation
Hunan Provincial Science and Technology Plan of China(Nos.10JJ7002, 2011FJ2001,2012TF1003)