Regenerative shields are used by Borg drones and new Federation starships (USS Prometheus only ship known to equip such shields to date). Regenerative shields seem to work by analyzing nature and frequency of incoming weapon or weapon striking shields in order to adapt so as to block future or current discharge more effectively (it also seems main reason why Federation always fights borg at almost point-blank range - short range does not allow Borg time to adapt to incoming weapons fire before it strikes hull.
For more about Star Trek shields in general, see here.
