backmen后卫backn.后面；背脊；靠背；后背；后卫vt.支持；后退adv.向后地adj.向后的；后面的；偏远的；过时的；积欠的back elector-motive force[电] 反电动势backfilling pipeline system充填管道系统back of a photographic lens照相透镜背面Back up a little further.再往后退一点。back-and-forth movement往复运动Back Zone Drafting Multiple后区牵伸倍数backfilled printed shirting单面浆印花布backcross allele management回交, 等位基因操纵backed-off milling cutter铲齿铣刀back analysis of parameters参数反演