基金Supported by The State Key Program of Fundam ental Research( G19980 613 0 8) ,National Natural Science Foundationof China( Nos.2 99710 0 5 ,2 0 0 2 3 0 0 5 ,2 0 0 710 0 4) ,and Scientific Research Foundation for the Returned Overseas ChineseScholars( S
