科研之友
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摘要
<正>在德国西部城市伍珀塔尔，有一条与众不同的铁路——这里的列车在轨道下方运行。Unlike ordinary train lines that stay determinedly fixed to dry land, suspension railways dangle (悬垂) beneath a track suspended from pylons (电缆塔).In 1893, Langen offered his suspension railway system to the city, Wuppertal,
