For a journal to be available through the University of Essex Library, the university pay for the licence to have the content. However, sometimes these licences expire and the library will look to find another database from which the source can be accessed. 

If there is a specific source that is no longer available, contact the library who will be able to further advise.

You could also use the 'request a resource' purchase suggestion form, if you think something should be added to the library collection.