@article{DAN_1984_276_6_a18,
     author = {A. M. Krasnosel'skii},
     title = {On forced periodic oscillations in the nonlinear systems},
     journal = {Doklady Akademii Nauk},
     pages = {1356--1359},
     year = {1984},
     volume = {276},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1984_276_6_a18/}
}