  We study coherent multiple Andreev reflections in quantum SNS junctions of
finite length and arbitrary transparency. The presence of superconducting bound
states in these junctions gives rise to great enhancement of the subgap
current. The effect is most pronounced in low-transparency junctions, $D\ll1$,
and in the interval of applied voltage $\Delta/2<eV<\Delta$, where the
amplitude of the current structures is proportional to the first power of the
junction transparency $D$. The resonant current structures consist of steps and
oscillations of the two-particle current and also of multiparticle resonance
peaks. The positions of the two-particle current structures have pronounced
temperature dependence which scales with $\Delta(T)$, while the positions of
the multiparticle resonances have weak temperature dependence, being mostly
determined by the junction geometry. Despite the large resonant two-particle
current, the excess current at large voltage is small and proportional to
$D^2$. Pacs: 74.50.+r, 74.80.Fp, 74.20.Fg, 73.23.Ad
