@article{DE_1978_14_2_a1,
     author = {N. N. Vasil'eva},
     title = {Separatrices of saddle periodic solutions of {Duffing's} equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {201--211},
     publisher = {mathdoc},
     volume = {14},
     number = {2},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1978_14_2_a1/}
}