@article{DAN_1990_311_4_a0,
     author = {D. Bularas and N. I. Vulpe and K. S. Sibirskii},
     title = {The problem of the center ``in the large'' for a general quadratic},
     journal = {Doklady Akademii Nauk},
     pages = {777--780},
     publisher = {mathdoc},
     volume = {311},
     number = {4},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1990_311_4_a0/}
}