The PubMed Summary display format has changed to include information about the availability of free articles from publishers. In addition to the existing link on citations showing what is free in PubMed Central (PMC), a new link indicates if the article is freely available at the journal's Web site. Some citations have a link indicating the article is free from both PMC and the journal. The links all go to the AbstractPlus display where icon links to PMC and journal sites display.
For some LinkOut library participants, their subscriptions to journals that provide online access can greatly increase the number of "free" articles available to patrons as compared to what is shown by free indicators on the Summary display. Patrons can use My NCBI to create a filter for their library in order to easily determine what additional articles they can view. Instructions for creating filters can be found in the PubMed Help....
Here's a sample search with some examples of the flags. Look for the green text which says "Free article at journal site", "Free article in PMC", or "Free article in PMC | at journal site".
Here's my translation of the second paragraph above: The new free-article flags do not cover subsidized TA articles, or articles that are not OA but free to you because your employer has prepaid the access fees. However, you can still link to such articles from PubMed and filter your searches to display only such articles. BTW, this is in contrast to the practice at Google Scholar, whose free-article flag covers both OA articles and subsidized TA articles.
The open access movement:
Putting peer-reviewed scientific and scholarly literature
on the internet. Making it available free of charge and
free of most copyright and licensing restrictions.
Removing the barriers to serious research.