Zhi Qiang LI Liu Gen XUE College of Sciences,Beijing University of Chemical Technology,Beijing 100029,P.R.China College of Applied Sciences,Beijing University of Technology,Beijing 100022,P.R.China
Acta Mathematica Sinica, Chinese Series
.
2009, (02): 95
-102
.
DOI: 10.12386/A2009sxxb0035
