@article{JRAM_1979__0311_0312_152169,
     author = {M. Giaquinta and G. Modica},
     title = {Regularity results for some classes of higher order non linear elliptic systems.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {145--169},
     publisher = {mathdoc},
     volume = {0311_0312},
     year = {1979},
     zbl = {0409.35015},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1979__0311_0312_152169/}
}