  We develop a numerical scheme to investigate the high-order harmonic
generation (HHG) in intense laser-matter interactions. Tracing the time
evolution of every electronic laser-field-free state, we "observe" the HHG in a
time-integrated quantum transition picture. Our full-quantum simulations reveal
that continuum electrons with a broad energy distribution contribute equally to
one harmonic and the excited state also plays an important role in the
molecular HHG. These results imply a laser-intensity-dependent picture of
intramolecular interference in the HHG.
