中国科学院数学与系统科学研究院期刊网
AMS
Global Phase Portraits of Quadratic Systems with a Complex Ellipse as Invariant Algebraic Curve
Jaume LLIBRE, Claudia VALLS
Acta Mathematica Sinica . 2018, (5): 801 -811 .  DOI: 10.1007/s10114-017-5478-y