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@article{DE_1986_22_5_a29, author = {N. P. Morozov}, title = {Periodic solutions of the equation $\ddot x+\lambda f(ax+b\dot x)\dot x+x=0$}, journal = {Differencialʹnye uravneni\^a}, pages = {905--907}, publisher = {mathdoc}, volume = {22}, number = {5}, year = {1986}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1986_22_5_a29/} }
N. P. Morozov. Periodic solutions of the equation $\ddot x+\lambda f(ax+b\dot x)\dot x+x=0$. Differencialʹnye uravneniâ, Tome 22 (1986) no. 5, pp. 905-907. http://geodesic.mathdoc.fr/item/DE_1986_22_5_a29/