@article{DE_1977_13_6_a25,
     author = {V. E. Chernyshev},
     title = {The existence of saddle periodic solutions of {Duffing's} equation without dissipation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1145--1148},
     publisher = {mathdoc},
     volume = {13},
     number = {6},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1977_13_6_a25/}
}