博后是什么签证？
博士后，即Postdoctoral researcher(postdoc) 是指获得博士学位后在高校或者研究机构等从事一定期限研究工作的人，也指在博士毕业后继续攻读硕士学位或从事教学、科研工作的人员。 Post-doctor（a.） is a person who has been awarded a doctorate degree and continues to do research full time for two/three years in colleges or scientific research institutes as postgraduates under the guidance of professors after graduation， usually with no salary but free accommodation provided by their employers. They sometimes serve as assistant professors during this period， which they are not obliged to if so desired. In China ， people holding doctor degrees work as postdocs at most universities without pay. In Europe some countries refer to postdocs as “research Fellows”. However it seems that， though called fellows， these researchers are normally paid salaries rather than being supported on grants only like academic fellows. For example， at Cambridge University Research Fellows receive between £20，000 and £40，000 per annum depending upon experience， while in U.K. universities generally lecturers start from about£30，000 and associate professors around£50，000．
1984 年以前，我国实行的是学位制，没有“博士后”这一概念。当时获得博士学位者如拟进一步研究探索或在某一学科领域内扩大成果，往往以 2～4年的时限到指定的有关单位作定期或不定期的博士后研究工作。这种制度被称为“博士后流动站”(Post Doctoral Contingency Scheme)；“博士后研究人员”(简称“博士后”)则被称作“特别研究者”(Particular Researcher)。 1985年6月，全国博士后管理委员会成立，负责全国博士后制度的管理工作。同年11月，国务院发布《关于试行博士后制度的规定》，规定设立博士后科研流动站和博士后科研工作站，招收博士后研究人员，明确博士后是获准进入博士后科研流动站从事科学研究工作的博士学位获得者。博士后研究人员在站期间的基本待遇由劳动保险费和单位工资两部分组成。同时设立了博士后科学基金会。
The system was initiated in October l978 when four Chinese universities (Peking， Tsinghua， Zhejiang & Fudan ) established "PostDoctorial Training Centers" for scholars who received Ph Ds， to continue to conduct further study and exploration within certain fields of speciality and gain further achievements after obtaining such qualification. The term "after earning his PhD" came into wide use then instead of "Specialist with Ph D degree"， referring to those postgraduate students who have obtained both Ph D and Master's Degree， hence the abbreviated form PHD. As a result， we can see that "after" here