2. Theory that the
sur-hinge-point is pivotal point provides theoretical basis for the filling to prevent the instability of the basic roof.

铰接结构的上铰接点是岩层控制的关键点,这为现场实施充填以防止基本顶失稳的动力作用,提供了理论依据。
3. The Ltd. company is a hitch enterprise specialized in developing, manufacturing and selling oil
sur-vey instruments, and providing technique service.

北京北正伟业科技有限公司是专业从事油田测量仪器开发、生产、销售与技术服务的高科技企业。