@article{DE_1968_4_3_a7,
     author = {E. A. Grebenikov},
     title = {Certain estimates of the method of averaging for multifrequency systems of ordinary differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {459--473},
     publisher = {mathdoc},
     volume = {4},
     number = {3},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1968_4_3_a7/}
}