  Within the framework of a dinuclear system (DNS) model, the
evaporation-residue excitation functions and the quasi-fission mass yields in
the $^{48}$Ca induced fusion reactions are investigated systematically and
compared with available experimental data. Maximal production cross sections of
superheavy nuclei based on stable actinide targets are obtained. Isotopic
trends in the production of the superheavy elements Z=110, 112-118 based on the
actinide isotopic targets are analyzed systematically. Optimal evaporation
channels and combinations as well as the corresponding excitation energies are
proposed. The possible factors that influencing the isotopic dependence of the
production cross sections are analyzed. The formation of the superheavy nuclei
based on the isotopes U with different projectiles are also investigated and
calculated.
