Upgrading from:

Calculus`DSolveIntegrals`

The functionality of Calculus`DSolveIntegrals` is now available in the built-in Mathematica kernel function DSolve.

Find a complete integral of D[u[x,y],x]*D[u[x,y],y]1:

Version 5.2 << Calculus`DSolveIntegrals`; CompleteIntegral[D[u[x, y], x]*D[u[x, y], y] ⩵ 1, u[x, y], {x, y}]