[1]Schlz F. Regularity for certain quasilinear elliptic systems of divergence. Ind Uni Math J, 1990, 39(2):303-314

[2]Tan Z, Yan Z Q. Regularity of weak solutions to some degenerate elliptic equations and obstacle problem.Math J, 1993, 9(2):143-156

[3]Giaquinta M. Multiple integrals in the calculus of variations and nonlinear elliptic systems. Ann of Math Studies 105. Princeton, New Jersey: Princeton Univ, Press 1983

[4]Tolksdorf P. Regularity for a more general class of quasilinear elliptic equations. J Diff Equ, 1984, 51:126-150

[5]Fuchs M. H¨older continuity of the gradient for degenerate variational inequalities. Nonlinear Analysis,TMA, 1990, 15(1):85-100

[6]Kan Q K, Shu S Q. Regularity of weak solution to a class of degenerate elliptic equations (in Chinese). to appear

[7]Gerhardt C. Global C1,1-regularity for solution of quasilinear variational ineqalities. Arch Rat Mech Anal,1985, 89:83-92

[8]Giaquinta M, Giusti E. Nonlinear elliptic systems with quadratic growth. Mannuscr Math, 1978, 24:323-349

[9]Giaquinta M, Modica G. Regularity results for some class of higher order nonlinear elliptic systems. J Reine Angew Math, 1979, 311-312:145-169

[10]Giaquinta M, Modica G. Almost everywhere regularity results for solutions of nonlinear elliptic systems.Mannuscr Math, 1979, 28:109-158

[11]Campanato S. Equazioni ellittiche de II0 ordine e spazi C(2,). Ann Math Pura Appl, 1965, 69:321-381

[12]Morrey C B. Second order elliptic systems of differential equations. In:Ann of Math Studies 33 Princeton,New Jersey:Princeton Univ Press, 1954. 101-159

[13]Gehering F W. The Lp- integrability of the partial derivatives of a quasiformal mapping. Acta Math,1973, 130:265-277

[14]Chen Y Z, Wu L C. Elliptic equations and elliptic systems of second order(in Chinese), Beijing: Science Press, 1997