@article{IVM_1966_4_a18,
     author = {A. T. Turaev},
     title = {Certain methods of obtaining criteria for the existence and nonexistence of periodic solutions of a~differential equation},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {129--133},
     year = {1966},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1966_4_a18/}
}