@article{DE_1995_31_12_a15,
     author = {V. V. Amel'kin},
     title = {On conditions for the existence of limit cycles in two-dimensional autonomous systems of differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2070--2072},
     publisher = {mathdoc},
     volume = {31},
     number = {12},
     year = {1995},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1995_31_12_a15/}
}