[1] Furumochi T.Existence of periodic solutions of one-dimensional differential-delay equations [J].Tohoku Math J, 1978, 30(1):13-35.
[2] Cunningham W J.A nonlinear differential-difference equation of growth [J].Proc Nat Acad Sci, 1954, 40(5):709-713.
[3] Jones G S.The existence of periodic solutions of f′(x)=-αf(x(t-1)){1+f(x)}[J].J Math Anal Appl, 1962, 5(3):435-450.
[4] Belair J, Mackey M C.Consumer memory and price fluctuation commodity markets:an integro-differential model [J].J Diff Eq, 1989, 1(2):299-325.
[5] Kaplan J, Yorke J.Ordinary differential equations which yield periodic solutions of differential delay equations [J].J Math Anal Appl, 1974, 48(2):317-327.
[6] Nussbaum R D.Periodic solutions of special differential delay equations:an example in non-linear functional analysis [J].Proceedings of the Royal Society of Edinburgh, 1978, 81A(1):131-151.
[7] Li J, He X.Multiple periodic solutions of differential delay equations created by asymptotically linear Hamiltonian systems [J].Nonlinear Anal TMA, 1998, 31(1):45-54.
[8] Li J, He X, Liu Z.Hamiltonian symmetric groups and multiple periodic solutions of differential delay equations [J].Nonlinear Anal TMA, 1999, 35(4):457-474.
[9] Fei G.Multiple periodic solutions of differential delay equations via Hamiltonian systems(Ⅰ)[J].Nonlinear Anal TMA, 2006, 65(1):25-39.
[10] Fei G.Multiple periodic solutions of differential delay equations via Hamiltonian systems(Ⅱ)[J]. Nonlinear Anal TMA, 2006, 65(1):40-58.
[11] Rabinowitz P H.Minimax methods in critical point theory with applications to differential equations [C]//CBMS Regional Conf Ser in Math.Miami, USA, 1986:32-33.
[12] Chang K C.Critical point theory and applications [M].Shanghai:Shanghai Science and Technology Press, 1986.(in Chinese)
[13] Fei G.On periodic solutions of superquadratic Hamiltonian systems [J].Electronic J Diff Eq, 2002, 2002(8):1-12.
[14] Long Y, Zehnder E.Morse theory for forced oscillations of asymptotically linear Hamiltonian systems [C]//Stochastic Processes in Physics and Geometry.Singapore:World Scientific, 1990:528-563.