@article{JRAM_1980__316_152246,
     author = {M. Giaquinta and J. Necas},
     title = {On the regularity of weak solutions to non linear elliptic systems of partial differential equations.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {140--159},
     publisher = {mathdoc},
     volume = {316},
     year = {1980},
     zbl = {0435.35036},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1980__316_152246/}
}