@article{DE_1970_6_10_a20,
     author = {N. N. Vinogradov},
     title = {The existence of a periodic solution of a nonlinear system of three differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1901},
     publisher = {mathdoc},
     volume = {6},
     number = {10},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_10_a20/}
}