@article{DE_1980_16_1_a12,
     author = {S. I. Pokhozhaev},
     title = {Periodic solutions of some nonlinear systems of ordinary differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {109--116},
     publisher = {mathdoc},
     volume = {16},
     number = {1},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1980_16_1_a12/}
}