@article{MZM_1977_21_6_a8,
     author = {N. A. Izobov},
     title = {The transfer of the {Lyapunov} integral criterion to two-dimensional periodic systems of second order},
     journal = {Matemati\v{c}eskie zametki},
     pages = {817--828},
     publisher = {mathdoc},
     volume = {21},
     number = {6},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1977_21_6_a8/}
}