  We have elucidated the nature of the electron correlation effect in uranium
compounds by imaging the partial $\mathrm{U}~5f$ density of states (pDOS) of
typical itinerant, localized, and heavy fermion uranium compounds by using the
$\mathrm{U}~4d-5f$ resonant photoemission spectroscopy. Obtained
$\mathrm{U}~5f$ pDOS exhibit a systematic trend depending on the physical
properties of compounds. The coherent peak at the Fermi level can be described
by the band-structure calculation, but an incoherent peak emerges on the higher
binding energy side ($\lesssim 1~\mathrm{eV}$) in the \Uf pDOS of localized and
heavy fermion compounds. As the $\mathrm{U}~5f$ state is more localized, the
intensity of the incoherent peak is enhanced and its energy position is shifted
to higher binding energy. These behaviors are consistent with the prediction of
the Mott metal-insulator transition, suggesting that the Hubbard-$U$ type
mechanism takes an essential role in the $5f$ electronic structure of actinide
materials.
