@article{DE_1965_1_3_a6,
     author = {N. N. Vinogradov},
     title = {Some existence theorems for a periodic solution of an autonomous system of six differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {330--334},
     publisher = {mathdoc},
     volume = {1},
     number = {3},
     year = {1965},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1965_1_3_a6/}
}