@article{DE_1982_18_5_a8,
     author = {V. A. Lunkevich and K. S. Sibirskii},
     title = {Integrals of a general quadratic differential system in cases of the center},
     journal = {Differencialʹnye uravneni\^a},
     pages = {786--792},
     publisher = {mathdoc},
     volume = {18},
     number = {5},
     year = {1982},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1982_18_5_a8/}
}