Lexis and Nexis are two different services. First select a library, then a file or files. The first screen displays available libraries. Type in the code for the library you desire. Lexis Libraries are those in the public domain.
Nexis files are commercial vendors.
Medis are medically oriented. Duplication does exist between some libraries, and you may retrieve some duplicate citations. You may search only one library at a time. Selecting Files Not all files are available to special educational discount subscribers, most of these are full text business, medical or legal journals. You may search more than one file at a time.