@article{DE_1976_12_2_a11,
     author = {L. A. Cherkas},
     title = {Conditions for a center for a certain {Li\'enard} equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {292--298},
     publisher = {mathdoc},
     volume = {12},
     number = {2},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1976_12_2_a11/}
}