Beginning on December 28, 2007, citations from the 1949 Current List of Medical Literature(CLML) were added to the OLDMEDLINE subset in PubMed. These 55,557 citations have not yet been assigned Medical Subject Headings (MeSH). To search PubMed for citations originating from OLDMEDLINE, add the following to your search statement in the Search box: AND jsubsetom. For additional information about the OLDMEDLINE data project, see http://www.nlm.nih.gov/databases/databases_oldmedline.html.
In addition, many individual journals have digitized their back content and deposited the full text issues in PubMed Central. These old articles – some back to 1865 – are also in PubMed.