When you search in Explore Chicago Collections, you are searching the full text of a record. This means that you will be able to find any terms you search for, no matter where they are in the record.
To search for an exact phrase, put the term you are looking for within quotation marks.
You can also search with wildcards. This means that the system will search any combination of letters following the wildcard character (*).
So searching for arg* will find results not only for Argonne National Laboratory but also for Argyle Street and Argentina.