@article{DE_1970_6_12_a0,
     author = {V. V. Amel'kin and N. A. Lukashevich},
     title = {The periods of the solutions of certain autonomous systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2115--2120},
     publisher = {mathdoc},
     volume = {6},
     number = {12},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_12_a0/}
}