@article{DE_1989_25_11_a3,
     author = {Bularas Driss and N. I. Vulpe and K. S. Sibirskii},
     title = {Solution of a problem of the center ``in the large'' for a general quadratic differential system},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1856--1862},
     publisher = {mathdoc},
     volume = {25},
     number = {11},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1989_25_11_a3/}
}