@article{DE_1985_21_9_a21,
     author = {M. N. Eliseenko},
     title = {Periodic solutions of second-order ordinary differential equations not solved with respect to the derivative},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1618--1621},
     publisher = {mathdoc},
     volume = {21},
     number = {9},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1985_21_9_a21/}
}