This paper is supported by the Special Doctoral Grant of the Ministry of Education of China （No. 98049114） and the National Natural Science Foundation of China （No. 49972023）.
基金This paper is supported by the Special Doctoral Grant of the Ministry ofEducation of China(No.98049114)and the National Natural Science Foundation of China(No.49972023).
文摘This paper is supported by the Special Doctoral Grant of the Ministry of Education of China （No. 98049114） and the National Natural Science Foundation of China （No. 49972023）.
