Voir la notice de l'article provenant de la source Math-Net.Ru
@article{DE_1967_3_11_a6, author = {A. M. Samoilenko}, title = {Periodic solutions of second-order nonlinear equations}, journal = {Differencialʹnye uravneni\^a}, pages = {1903--1912}, publisher = {mathdoc}, volume = {3}, number = {11}, year = {1967}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1967_3_11_a6/} }
A. M. Samoilenko. Periodic solutions of second-order nonlinear equations. Differencialʹnye uravneniâ, Tome 3 (1967) no. 11, pp. 1903-1912. http://geodesic.mathdoc.fr/item/DE_1967_3_11_a6/