Sometimes you will come across a resource in Summon that is marked (see example above). This means that Summon cannot give you access to the full text online, and the library probably does not have the item in hard copy.
Or you may have a citation from another source, such as a bibliography, and find that Summon has no record of it.
If you'd like to track down one of these citations, go to the relevant tab of this guide. The final tab explains how to find even more citations in Summon.
Tracking down a resource from a citation is sometimes hard. Do not hesitate to contact the library if you need help.