@article{IVM_1991_1_a1,
     author = {E. V. Voskresenskii},
     title = {Periodic solutions of perturbed differential equations},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {11--14},
     publisher = {mathdoc},
     number = {1},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1991_1_a1/}
}