@article{DE_1994_30_9_a1,
     author = {V. N. Gorbuzov},
     title = {On a second-order differential system and its periodic solutions},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1487--1497},
     year = {1994},
     volume = {30},
     number = {9},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1994_30_9_a1/}
}