@article{DE_1970_6_2_a19,
     author = {N. A. Zboychik},
     title = {Quadratic integrals of linear systems of differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {381--384},
     publisher = {mathdoc},
     volume = {6},
     number = {2},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_2_a19/}
}