The library doesn't have full text access to all the content available in ScienceDirect or JSTOR. Here are some suggestions for getting to content you can access.
ScienceDirect
Look for articles that have a Download PDF link or a green circle with Full text access, Open access, or Open archive next to it.
JSTOR
In JSTOR, check the Refine Results section on the left side of your search results. Make sure Access Level is set to Read and download.
You can read more about finding content you have access to from JSTOR's support page.
Finally, you may request an article through interlibrary loan.