2045| 0
|
[执业医师] 先将总体的单位按某种特征分为若干次级总体,再从各次级总体中进行单纯随机抽样,共同 |
手机版|会员|至尊|接种|公卫人 ( 沪ICP备06060850号-3 )
GMT+8, 2024-6-1 13:27 , Processed in 0.111047 second(s), 6 queries , Gzip On, MemCached On.
Powered by Discuz! X3.4
© 2001-2023 Discuz! Team.