@article{DE_1970_6_3_a22,
     author = {L. N. Karmov},
     title = {The method of differentiation with respect to a parameter as applied to the problem of determining periodic solutions of differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {569--570},
     publisher = {mathdoc},
     volume = {6},
     number = {3},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_3_a22/}
}