Lu S, Ge W. Periodic solutions for a kind of Liénard equations with deviating arguments[J]. J Math Anal Appl, 2004,249:231-243.
[2]
Liu B, Huang L. Existence and uniqueness of periodic solutions for a kind of Liénard equation with a deviating argument[J]. Applied Mathematics Letters, 2008,21:56-62.
[3]
Gaines R E, Mawhin J. Coincide degree and nonlinear differential equations, in:lecture notes in math[M]. Berlin:Springer-Verlag, 1977.
[4]
Du B, Guo L, Ge W. Periodic solutions for generalized Liénard neutral equation with variable parameter[J]. Nonlinear Anal, 2009,70:2387-2394.
[5]
Petryshyn W V, Yu Z S. Existence theorems for higher order nonlinear periodic boundary value problems[J]. Nonlinear Anal, 1982,9:943-969.
[6]
Liu Z D, Mao Y P. Existence theorem for periodic solutions of higher order nonlinear differential equations[J]. J Math Anal Appl, 1997,216:481-490.