@article{DE_1985_21_4_a0,
     author = {A. G. Baskakov},
     title = {The averaging method in the theory of perturbations of linear differential operators},
     journal = {Differencialʹnye uravneni\^a},
     pages = {555--562},
     publisher = {mathdoc},
     volume = {21},
     number = {4},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1985_21_4_a0/}
}