@article{DE_2000_36_1_a13,
     author = {A. P. Sadovskii},
     title = {Center conditions and limit cycles in a cubic system of differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {98--102},
     publisher = {mathdoc},
     volume = {36},
     number = {1},
     year = {2000},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_2000_36_1_a13/}
}