@article{DAN_1991_317_6_a9,
     author = {L. M. Litvin and V. V. Rudnev},
     title = {On almost-periodic oscillations in mechanical systems},
     journal = {Doklady Akademii Nauk},
     pages = {1329--1333},
     year = {1991},
     volume = {317},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1991_317_6_a9/}
}