@article{DE_1970_6_2_a18,
     author = {E. A. Nazarov},
     title = {Conditions for the existence of periodic trajectories in dynamic systems with cylindrical phase space},
     journal = {Differencialʹnye uravneni\^a},
     pages = {377--380},
     publisher = {mathdoc},
     volume = {6},
     number = {2},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_2_a18/}
}