Josephson dynamics and Shapiro steps at high transmissions: current bias regime.

We investigate Josephson dynamics of highly transparent superconducting nanojunctions at subgap voltages and temperatures. In this limit, intrinsic dissipation in such junctions turns out to be sub-Ohmic, which yields a linear dependence of the average voltage on the bias current slightly exceeding the critical one . We demonstrate a strong impact of intrinsic sub-Ohmic dissipation on integer Shapiro steps appearing on the - curve in the presence of external microwave radiation.