@article{IVM_1970_3_a9,
     author = {V. S. Nustrov},
     title = {The periodic solutions of systems that are close to nonlinear systems in the case of principal resonance},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {63--69},
     publisher = {mathdoc},
     number = {3},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1970_3_a9/}
}