@article{DE_1990_26_2_a22,
     author = {A. K. Demenchuk},
     title = {Periodic solutions of {Hamiltonian} systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {348--350},
     year = {1990},
     volume = {26},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1990_26_2_a22/}
}