%0 Journal Article %A A. P. Oskolkov %T Prior estimates of the first derivatives for two-dimensional quasi-linear strongly elliptic systems %J Trudy Matematicheskogo Instituta imeni V.A. Steklova %D 1966 %P 192-202 %V 92 %I mathdoc %U http://geodesic.mathdoc.fr/item/TM_1966_92_a12/ %G ru %F TM_1966_92_a12