@article{DE_1969_5_2_a18,
     author = {V. V. Amel'kin},
     title = {The periodic solutions of a certain class of nonlinear systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {385--388},
     publisher = {mathdoc},
     volume = {5},
     number = {2},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1969_5_2_a18/}
}