@article{TM_1987_180_a44,
     author = {Yu. I. Volkov},
     title = {On approximation in the mean by multidimensional positive linear operators},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {85--86},
     year = {1987},
     volume = {180},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_1987_180_a44/}
}