Mark Zuckerberg predicts the site's userbase might even reach one billion.
2
目的了解甲型流感病毒H9N2亚型毒株在深圳地区鸡群和人群中的分布。
Objective To understand the distribution of influenza a H9N2 virus in chickens and men in Shenzhen area.
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方法采用多阶段整群抽样和配额抽样相结合的方法，对深圳市1 320名居民进行入户问卷调查。
Methods Random sample were obtained from the whole population by multiple stratified cluster and 1 320 objects were surveyed in their own homes by questionnaires.
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