@article{DE_1969_5_11_a13,
     author = {V. V. Amel'kin},
     title = {The periodic solutions of a certain nonautonomous system},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2085--2086},
     publisher = {mathdoc},
     volume = {5},
     number = {11},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1969_5_11_a13/}
}