You can if you precede the tag in the search with a minus (-):
shell [cmd] -[linux]
The following links pop for searches across the SOFU for questions that mention cmd tagged shell but not tagged linux.
StackOverflow: http://stackoverflow.com/search?q=%22cmd%22+[shell]+[-linux]
ServerFault: http://serverfault.com/search?q=%22cmd%22+[shell]+[-linux]
SuperUser: http://superuser.com/search?q=%22cmd%22+[shell]+[-linux]