@article{DAN_1979_249_6_a3,
     author = {V. V. Kozlov},
     title = {Topological obstructions to the integrability of natural mechanical systems},
     journal = {Doklady Akademii Nauk},
     pages = {1299--1302},
     publisher = {mathdoc},
     volume = {249},
     number = {6},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1979_249_6_a3/}
}