方法描述DXA骨密度仪测量技术原理和参数，阐述当前骨吸收测量技术的利与弊。
Methods The physical meaning of BMD and other relative parameter of DXA was described. The advantages and disadvantages of current absorptiometric techniques were presented.
本文介绍了其性能特点、结构形式、技术参数、工作原理和电路图。
Its performance characteristic, structure, technical parameter, working principle and circuit diagram are introduced in this paper.
介绍隧道通风控制与监测系统，包括基本技术条件、控制原理、监测参数和实施。
The-tunnel ventilation control and monitoring system is introduced. The contents include the basic technical requirement, control principle, monitoring parameters and implementation.
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