@article{IVM_1957_1_a12,
     author = {E. I. Zheleznov},
     title = {Sufficient conditions for the existence of limit cycles},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {127--132},
     publisher = {mathdoc},
     number = {1},
     year = {1957},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1957_1_a12/}
}