@article{DAN_1962_143_2_a13,
     author = {T. F. Ivanov},
     title = {Determination of periodic motions in conservative systems with one degree of freedom},
     journal = {Doklady Akademii Nauk},
     pages = {297--300},
     publisher = {mathdoc},
     volume = {143},
     number = {2},
     year = {1962},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1962_143_2_a13/}
}