Or, you could do as follows:
Introduce:
[tex]x=u^{6}\to\frac{dx}{du}=6u^{5}\to{dx}=6u^{5}du[/tex]
Then,
[tex]\int\frac{dx}{\sqrt{x}-\sqrt[3]{x}}=\int\frac{6u^{5}}{u^{3}-u^{2}}du=\int\frac{6u^{3}}{u-1}du=6\int({u}^{2}+u+1+\frac{1}{u-1})du[/tex]
which is easily integrated.