@article{TSP_2009_27_27_a1,
     author = {R. V. Guseinov},
     title = {On the number of negative spectrum points of elliptic operators},
     journal = {Trudy Seminara im. I.G. Petrovskogo},
     pages = {67--73},
     year = {2009},
     volume = {27},
     number = {27},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TSP_2009_27_27_a1/}
}