The theory of medical microtron is introduced.The theory of medical runway microtron is expressed and its characteristics are compared with electron linear accelerator.

着重介绍电子回旋原理，重点介绍跑道式电子回旋的工作原理，并对电子回旋和电子直线的特点进行。

Counterfort retaining walls are optimized in the paper, using the optimum program, costs of different counterfort retaining wall parameters were calculated and based on the contrast analysis.

本文对扶壁式挡土墙进行优化计算,利用优化设计程序对不同参数下的截面状态和工程造价进行分析。