You Hui SU Mathematics and Physical Sciences Technology,Xuzhou Institute of Technology,Xuzhou 221008,P.R.China School of Mathematics and Statistics,Lanzhou University,Lanzhou 730000,P.R.China Wan Tong LI School of Mathematics and Statistics,Lanzhou Univer
Acta Mathematica Sinica, Chinese Series
.
2009, (01): 183
-198
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DOI: 10.12386/A2009sxxb0019