how can I search by the ISSN number
There is a page where you can search for journals by their ISSN, which will link you out to the database that may have your article full-text. On the Find Articles page, the top in the list of links is the A-Z of Online Journal Titles. This link takes you to the page that searches by journal title, but if you click on "Locate" above the search area, you can search by ISSN. When you click Go it will pull up the listing for the journal associated with that ISSN beneath your search box.
Under the title [in red], it shows you which databases have that journal full text and the years available (if no results are found, it could be that we do not subscribe to a database that has that journal or there was a typo in your entry). If you click on the database name that has your years covered, it should take you to the database page for that journal specifically.
I hope this helps!