@article{DAN_1964_156_5_a8,
     author = {M. A. Krasnosel'skii and V. V. Strygin},
     title = {Some criteria for the existence of periodic solutions of ordinary differential equations},
     journal = {Doklady Akademii Nauk},
     pages = {1022--1024},
     publisher = {mathdoc},
     volume = {156},
     number = {5},
     year = {1964},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1964_156_5_a8/}
}