摘要
Without loss of generality, the quadratic system （Ⅱ）<sub>m=0</sub> can be assumed as follows:Generally, system （1） has four singular points, focus （node） 0（0,0）, R（-1/a,y<sub>2</sub>）, saddle N（0, 1）, M（-1/a,y<sub>1</sub>）, where y<sub>1, 2</sub>=[a±（a<sup>2</sup>-4（l-aδ））<sup>1/2</sup>]/2a.
基金
Project supported by the National Natural Science Foundation of China
