@article{IVM_1968_7_a7,
     author = {N. V. Medvedev},
     title = {A~certain method of finding periodic solutions of a~system of differential equations},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {51--55},
     year = {1968},
     number = {7},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1968_7_a7/}
}