This paper by use of perturbation method found asymptotic periodic solution of piston stroke, and found rational periodic for periodic external force.

本文用摄动方法求得了活塞行程的渐近周期解，且为周期性外力求出合理的周期。

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In this paper we prove some theorems on harmonic solutions of some second-order nonlinear equations under a periodic external force.

本文给出了某些二阶非线性微分方程在周期外力作用下存在调和解的若干定理。

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