  We investigate the structure and stability of hypercritical accretion flows
around stellar-mass black holes, taking into account neutrino cooling, lepton
conservation, and firstly a realistic equation of state in order to properly
treat the dissociation of nuclei. We obtain the radial distributions of
physical properties, such as density, temperature and electron fraction, for
various mass accretion rates $0.1\sim 10M_{\odot}{\rm s}^{-1}$. We find that,
depending on mass accretion rates, different physics affect considerably the
structure of the disk; most important physics is (1) the photodissociation of
nuclei around $r\sim 100r_g$ for relatively low mass accretion rates
($\dot{M}\sim 0.01-0.1M_{\odot} {\rm s}^{-1}$), (2) efficient neutrino cooling
around $r\sim 10-100r_g$ for moderately high mass accretion rate ($\dot{M}\sim
0.2-1.0M_{\odot}{\rm s}^{-1}$), and (3) neutrino trapping ($r\sim 3-10r_g$) for
very high mass accretion rate ($\dot{M}\gtrsim 2.0M_{\odot}{\rm s}^{-1}$). We
also investigate the stability of hypercritical accretion flows by drawing the
thermal equilibrium curves, and find that efficient neutrino cooling makes the
accretion flows rather stable against both thermal and viscous modes.
