@article{DE_1972_8_7_a6,
     author = {L. A. Cherkas and L. I. Zhilevich},
     title = {The limit cycles of certain differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1207--1213},
     publisher = {mathdoc},
     volume = {8},
     number = {7},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1972_8_7_a6/}
}