@article{AA_1991_3_5_a10,
     author = {V. A. Yakubovich},
     title = {Nonoscillation of linear periodic {Hamiltonian} equations and related problems},
     journal = {Algebra i analiz},
     pages = {229--253},
     year = {1991},
     volume = {3},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AA_1991_3_5_a10/}
}