简述蜗杆传动主要特点?
参考答案:
(1)承载能力较大;
(2)传动比大,而且准确;
(3)传动平稳、无噪声;
(4)具有自锁作用;
(5)传动效率低;
(6)不能任意互换啮合。
— Does anyone know _____?
— I hear that he was born in Sweden. [ ]
A. what he is
B. when he was born
C. where he comes from
D. which country is he from
青霉素钠注射剂的皮试药液浓度应为
A.100U/mlB.250U/mlC.500U/mlD.750U/mlE.1000U/ml