钻孔轴线歪斜的原因有哪些?
参考答案:
钻孔轴线歪斜的原因有:1)钻床主轴与各个工作台面不垂直。2)工件有砂眼、气孔。3)钻头横刃长、角度不对称。4)进给量大,造成钻头弯曲。
睾丸内合成睾酮的细胞是()
A.生精细胞
B.支持细胞
C.间质细胞
D.成纤维细胞
E.肌样细胞
The major goal of USB was to define an external expansion bus which makes adding (71) to a PC as easy as hooking up a telephone to a wall-jack. USB 2.0 is an evolution of the USB 1.1 (72) , providing a higher performance interface.
A.protocol
B.specification
C.prescript
D.rule