I don’t believe that the SDMB search function has that capability. If you’re looking for older threads, try using the search function on boardreader.com. They store the text from the SDMB, as well as other boards, on their site. Just add the string straightdope to your query to get threads from the SDMB exclusively. In other words, if you’re looking for the string Operational Support Systems, then search for straightdope “Operational Support Systems”.