  In this thesis, a unified approach to prove the boundedness of gradients of
solutions to degenerate and singular elliptic and parabolic phi-Laplacian
systems is presented. At first, a Cacciopoli-type energy inequality with an
additional function f which can be chosen freely is proven. Then, Di Giorgi's
method is applied using level sets which will lead to L-infinity-estimates on
the gradient of the weak solution.
