PM,
1st segment - 35 feet screen to gear up (turbojet only; 50 feet otherwise)
2nd segment - gear up to acceleration height (min 400 feet), flown at takeoff power and V2 to V2+15
3rd segment - acceleration height to clean configuration, flown at takeoff power and minimum climb rate
4th segment - clean configuration to 1500 feet, flown at maximum continuous power and clean min maneuvering speed
At least, that's as far as I understand it based on the Boeing AFM...but if I've learned anything in this business, it is that there is always a exception.