中文摘要：

讨论了Duffing方程x″＋g（x）=p（t）在满足一些对称条件时对称周期解的分布情况.用相平面定性分析的方法,得到了在某种次线性条件下,对称周期解的稠密性分布结果.

英文摘要：

We discuss the distribution of the symmetric periodic solutions of Duffing equation x″＋g（x）=p（t） while the disturbed term p（t） is a symmetric function.We get the result that the symmetric periodic solutions are densely distributed through the analysis way in the phase plane.