中国科学院数学与系统科学研究院期刊网
The Generalized Focal Values and Bifurcation of Limit Cycles for Quasi Quadratic Systems
Yi Rong LIU
Acta Mathematica Sinica, Chinese Series . 2002, (4): 671 -682 .  DOI: 10.12386/A2002sxxb0089