Libkey.io allows you to search for an article using its Document Object Identifier (DOI) or PubMed Identifier (PMID). If you have never used a LibKey product before, the first time you visit libkey.io you will see a simple look-up page where you are invited to find an article by DOI or PMID. This page is only shown if an affiliation has not yet been set. Once you submit a DOI or PMID, you will set your organization to Northwestern University:

Libkey.io will rout you to a PDF of the article if one is available through the library's paid subscription content or open access. If neither option is available it will rout to document delivery services such as Article Galaxy Scholar or Interlibrary Loan.