@article{DE_1999_35_3_a0,
     author = {E. P. Volokitin and S. A. Treskov},
     title = {On periodic solutions of a system of differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {291--295},
     publisher = {mathdoc},
     volume = {35},
     number = {3},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1999_35_3_a0/}
}