中国科学院数学与系统科学研究院期刊网
AMS
Uniqueness of Limit Cycle for the Quadratic Systems with Weak Saddle and Focus
Shen Qi ZHAO, Ping Guang ZHANG
Acta Mathematica Sinica . 2004, (4): 647 -652 .  DOI: 10.1007/s10114-004-0380-9