mining of shaft coal pillar的意思|示意
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竖井煤柱开采
mining of shaft coal pillar的网络常见释义
井筒煤柱开采 ... Retreating mining method后退式开采法(采矿) mining of shaft coal pillar井筒煤柱开采 mining-beneficiation complexn.采选联合企业,采选公司 ...