@article{DE_1970_6_3_a7,
     author = {V. S. Medvedev},
     title = {Sufficient conditions for the absence of integral cycles for dynamical systems on manifolds},
     journal = {Differencialʹnye uravneni\^a},
     pages = {454--466},
     publisher = {mathdoc},
     volume = {6},
     number = {3},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_3_a7/}
}