3Rogovchenko Yu V. On oscillation of a second order nonlinear delay differential equation. Funkcial.Ekvac. 2000, 43: 1-29.
4Jurang Yan. Oscillation theorems for second order linear differential equations with damping.Proc. Amer. math. Soc., 1986, 98: 276-282.
5Cecchi M and Marini M. Oscillatory and nonoscillatory behavior of a second order functional differential equation. Rocky Mount. J. Math., 1992, 22: 1259-1276.
6Ladde G S, Lakshmikantham V, and Zhang B G. Oscillation Theory of Differential Equations with Deviating Arguments. Marcel Dekker, New York, 1987.
7Cechi M.,Marini M..Oscillatory and nonoscillatory behavior of a second order functional differential equation[J].Rocky Mount.J.Math.,1992,22(4):1259-1276.
8Rogovchenko Yu.V..On oscillation of a second order nonlinear delay differential equation[J].Funkcial.Ekuac.2000,43:1-29.
9Yan J.R..Oscillation theorems for second order Linear differential equations wkh damping[J].Proc.Amer.Math.Soc,1986,98:276-282.
10Ladde G.S.,Lakshmikantham V.,Zhang B.G..Oscillation Theory of Differential Equations with Deviating Arguments[M].New York:Marcel Dekker,1987.