Submitted on: 13 June 2002.
Revised on: 26 June 2002.
Accepted on: 18 July 2002.
NULL
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http://reply.papertrans.cn/3/201/20024/20024-33.png
Submitted on: 03 September 2007.
Revised on: 12 October 2007.
Accepted on: 23 October 2007.
NULL
http://reply.papertrans.cn/3/201/20024/20024-35.png
Submitted on: 30 March 2014.
Revised on: 30 April 2014.
Accepted on: 08 May 2014.
NULL