[1] ZHOU Y,YU Y H.The Distrubution of Zeros of Difference Equations with Continuous Variables [J].Ann. Chinese Math.,1999,20A(3):295-300.[2] ZHOU Y.The Distrubution of Zeros of Solutions of Nonlinear Delay Difference Equations with Continuous Variables [J].Nonlinear Studies,2002,9(1):75-80.[3] AGARWAL R P,ZHOU Y.Oscillation of Partial Difference Equations with Continuous Variables [J].Math. Comput. Modelling,2000,31:17-29.[4] ERBE L H,KONG Q K,ZHANG B G.Oscillation for Functional Difference Equations [M].Inc.:Marcel Dekker,1995.[5] GY?;RI I,LADAS G.Oscillation Theory of Delay Differential Equations with Applications [M].Oxford:Clarendon Press,1991.[6] LADAS G,PAKULA L,WANG Z.Necessary and Sufficient Condtions for the Oscillations of Difference Euaqtions [J].Panamerican Math. J.,1992,2(1):17-26.[7] ZHANG Y Z,YAN J.Oscillation Criteria for Difference Equations with Continuous Arguments [J].Acta. Math. Sinica,1995,38:406-411.[8] ZHANG Z,BI P,CHEN J.Oscillation of Second Order Nonlinear Difference Equations with Continuous Variables [J].J. Math. Anal. Appl.,2001,255:349-357.