  We present the results of our ALMA $\lesssim$0.5 kpc-resolution dense
molecular line (HCN and HCO$^{+}$ J=2-1, J=3-2, and J=4-3) observations of 12
nearby (ultra)luminous infrared galaxies ([U]LIRGs). After matching beam sizes
of all molecular line data to the same values in all (U)LIRGs, we derive
molecular line flux ratios, by extracting spectra in the central 0.5, 1, 2 kpc
circular regions, and 0.5-1 and 1-2 kpc annular regions. Based on non-LTE model
calculations, we quantitatively confirm that the innermost ($\lesssim$0.5 kpc)
molecular gas is very dense ($\gtrsim$10$^{5}$ cm$^{-3}$) and warm
($\gtrsim$300 K) in ULIRGs, and that in one LIRG is also modestly dense
(10$^{4-5}$ cm$^{-3}$) and warm ($\sim$100 K). We then investigate the spatial
variation of the HCN-to-HCO$^{+}$ flux ratios and high-J to low-J flux ratios
of HCN and HCO$^{+}$. A subtle sign of decreasing trend of these ratios from
the innermost ($\lesssim$0.5 kpc) to outer nuclear (0.5-2 kpc) region is
discernible in a significant fraction of the observed ULIRGs. For two
AGN-hosting ULIRGs which display the trend most clearly, we find based on a
Bayesian approach that the HCN-to-HCO$^{+}$ abundance ratio and gas kinetic
temperature systematically increase from the outer nuclear to the innermost
region. We suggest that this trend comes from potential AGN effects, because no
such spatial variation is found in a starburst-dominated LIRG.
