@article{DE_1977_13_5_a18,
     author = {A. E. Gel'man},
     title = {A method of finding periodic solutions of autonomous systems of differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {949--950},
     publisher = {mathdoc},
     volume = {13},
     number = {5},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1977_13_5_a18/}
}