Slim disks have been received much attention because of the increasing evidence of supercritical accreting objects. In this paper, we make an attempt to construct a unified model in which the viscosity and the dimensionless accretion rate can span rather wide ranges. We replace blackbody radiation under the diffusion approximation with a bridged formula that accounts for both blackbody radiation and thermal bremsstrahlung in optically thick and thin cases, respectively. Thus this allows us to investigate the structures of and the emergent spectra from slim disks in a wider parameter space covering transition regions from optically thick to optically thin. We show that there is a maximum transition radius, roughly R-tr,R-max/R-g similar to 50 when (M)(C) similar to 15. The emergent spectra from the unified model of the accretion disk have been calculated. A simple model of the hot corona above the slim disk is taken into account for the hard X-ray spectrum in this paper based on the work of Wang and Netzer. We have applied the present model to the microquasar GRS 1915+105 and the narrow-line Seyfert 1 galaxies RE J1034+396 and Ark 564. Our model can explain well the broadband X-ray spectra of narrow-line Seyfert 1 galaxies, microquasars, and possible ultraluminous compact X-ray sources. The present model can be widely applied to candidates for supercritical accreting objects.