Some of the journals that we access to through our database subscriptions have an embargo—a period of time before articles can be accessed via the database.
Check our Publication Finder for the journal you are trying to access. Click on "Full Text Access" to see the dates of our subscription(s), and any notes about embargo periods.
It's also possible that the latest issue has had a publishing or indexing delay.
If you need access to an article you can't get through our catalogs, you can ask us for help or request it via InterLibrary Loan.