backward pig发育不良的仔猪backwardadj.向后的；落后的adv.向后backward-curved-blade fan后向曲叶式风机backward wave power amplifier回波功率放大器backward stroke of the piston活塞回程backward hierarchical pointer向后层次指针Backward production capability落后产能backward-wave tube amplifier返波管放大器backward and forward extrusion正反挤压backward differential equation后向差分方程Backward Wave Sweep Oscillator回波扫描振荡器backward interpolation formula后向插值公式