【摘要】 给出系统(E1),(E2)和(E3)等非线性微分系统存在闭轨的一些新的判定条件,推广了非线性微分系统极限环的存在性和唯一性许多这方面研究的结果,并大大改进了它们的某些条件．在这个基础上,还给出了系统(E1)和(E2)恰有一个极限环的一组充分条件．更多还原

【Abstract】 In this paper, we gave some new sufficient conditions of existence and uniqueness for certain nonlinear differential systems (E1),(E2) and (E3). Many known results of the existence and uniqueness of limit cycles for nonlinear differentinal systems are generalized and their conditions are improved greatly.更多还原