中文摘要：

SD振子是一类既含有光滑又含有非连续的非线性模型，这类模型在物理学上有广泛的应用。研究一类SD振子的周期轨道的周期的单调性问题。证明了该类SD振子的周期都是单调的。

英文摘要：

SD oscillator is a smooth and discontinuous nonlinear model,which has extensively applica-tions in physics.For periodic orbits of a class of SD oscillator,the monotonic problem of the period is studied.It is proven that the period function of the SD oscillator is monotone.