Shields are usually based, and disperce energy from phaser and disrupter weapons. Once, on a planet after the Dominion War, Star Fleet had installed cannons on the surface of the planets, in violation of treaty with the Klingons. The cannons' artillery were very dangerous and virtually unstoppable, because their frequency was ever-changing, allowing the torpeidos to pass right through the shields of the Star Ship present, in this case, the Enterprise-E, with Jean-Luc Picard in the command chair.

Source:

A Time to Heal