@article{DAN_1974_217_5_a8,
     author = {M. M. Khapaev},
     title = {On averaging in multifrequency systems},
     journal = {Doklady Akademii Nauk},
     pages = {1021--1024},
     publisher = {mathdoc},
     volume = {217},
     number = {5},
     year = {1974},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1974_217_5_a8/}
}