@article{DE_1999_35_1_a1,
     author = {Ya. I. Bigun and A. M. Samoilenko},
     title = {Justification of the averaging principle for multifrequency systems of differential equations with delay},
     journal = {Differencialʹnye uravneni\^a},
     pages = {8--14},
     publisher = {mathdoc},
     volume = {35},
     number = {1},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1999_35_1_a1/}
}