Periodic solutions of Lienard equations with superlinear asymmetric nonlinearities

摘要

This article deals with the existence of periodic solutions for a class of planar systems of the form (E) u' = v - F(t,u), v' = -g(t,u) related to the Lienard equation u" + f(u)u' + g(t,u) = 0, (1.1)