@article{DE_1983_19_11_a27,
     author = {O. I. Nikitin and A. I. Perov},
     title = {On the question of approximate determination of periodic solutions of differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2001--2004},
     publisher = {mathdoc},
     volume = {19},
     number = {11},
     year = {1983},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1983_19_11_a27/}
}