@article{DE_1981_17_11_a8,
     author = {L. A. Cherkas},
     title = {Bifurcations of limit cycles of a quadratic system with a change of parameter which rotates the field},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2002--2016},
     publisher = {mathdoc},
     volume = {17},
     number = {11},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1981_17_11_a8/}
}