应用常微分方程定性方法，得到了正平衡点的全局稳定性和非小振幅极限环的存在唯一性的充分条件。

By using the qualitative methods of ODE, the positive equilibrium's global stability and existence and uniqueness of non-small amplitude stable limit cycle were obtained.

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在此基础上，利用微分方程的环域定理获得了所述系统存在极限环的条件。

Then by using Poincare-Bendixson theorem sufficient conditions for the existence of limit cycles are obtained.

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