@article{DE_1976_12_7_a0,
     author = {V. V. Amel'kin and V. \`E. Zhavnerchik},
     title = {Periodic solutions of certain second order equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1147--1150},
     publisher = {mathdoc},
     volume = {12},
     number = {7},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1976_12_7_a0/}
}