“…Different approaches in the study of PDEs with gradient terms have been proposed: for example sub-and super-solutions, topological degree theory, mountain pass techniques. We mention, for instance, the pioneering works of Amann and Crandall [3], Brézis and Turner [4], Mawhin and Schmitt [22,23], Pokhozhaev [25] and the more recent contributions [1,7,9,10,13,26,27,29]. See also the very recent survey [8] and references therein.…”