  We present a self-consistent hydrodynamical simulation of a Milky Way-like
galaxy, at the resolution of 0.05 pc. The model includes star formation and a
new implementation of stellar feedback through photo-ionization, radiative
pressure and supernovae. The simulation resolves the structure of the
interstellar medium at subparsec resolution for a few cloud lifetimes, and at
0.05 pc for about a cloud crossing time. Turbulence cascade and gravitation
from the kpc scales are de facto included in smaller structures like molecular
clouds. We show that the formation of a bar influences the dynamics of the
central ~100 pc by creating resonances. At larger radii, the spiral arms host
the formation of regularly spaced clouds: beads on a string and spurs. These
instabilities pump turbulent energy into the gas, generally in the supersonic
regime. Because of asymmetric drift, the supernovae explode outside of their
gaseous nursery, which diminishes the effect of feedback on the structure of
clouds. The evolution of clouds is thus mostly due to fragmentation and gas
consumption, regulated mainly by supersonic turbulence. The transition from
turbulence supported to self-gravitating gas is detected in the gas density
probability distribution function at ~2000 cm^-3. The power spectrum density
suggests that gravitation governs the hierarchical organisation of structures
from the galactic scale down to a few parsecs.
