... pp. 2807–2813,2010.9 Y. Wang and W. Ge, Periodic solutions for Duffing equations with a p-Laplacian-like operator,”Computers & Mathematics with Applications, vol. 52, no. 6-7, pp. 1079–1088, ... most general forced form of the Duffing-typeequation isut σut ft, ut pt. 1.3Recently, many authors have studied the existence of periodic solutions of the ... no. 1, pp. 125–133, 1990.8 B. Du, C. Bai, and X. Zhao, “Problems of periodic solutions for a type of Duffing equation with state-dependent delay,” Journal of Computational and Applied Mathematics,...