@article{DE_1988_24_12_a0,
     author = {V. V. Amel'kin},
     title = {Existence of limit cycles of two-dimensional autonomous systems of differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2027--2032},
     publisher = {mathdoc},
     volume = {24},
     number = {12},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1988_24_12_a0/}
}