@article{RM_1966_21_3_a1,
     author = {M. A. Krasnosel'skii},
     title = {The theory of periodic solutions of non-autonomous differential equations},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {53--74},
     publisher = {mathdoc},
     volume = {21},
     number = {3},
     year = {1966},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1966_21_3_a1/}
}