Search with Xapian Guide
If your repository has Xapian search enabled for "Simple Search" (e.g. http://example.eprints.org/cgi/search/simple). Then you can take advantage of some useful features to make more effective queries. You should be able to tell whether you have Xapian search enabled by checking whether you have the option by relevance match in the list of ordering options. This in itself can be useful, as it will rank results where the words you are searching for occur more frequently, which can be useful if the words are likely to match against a lot of items.
If you want to search for a specific phrase then ensure the whole phrase is within quote marks:
"supply change management"
Some words but not others
If you prepend the words you want to find with a + and the words you do not want to find with a -:
+science -engineering +mathematics
This word near another word
If you put the phrase NEAR between the two words then it will find matches where the words have 10 or less words in between:
science NEAR mathematics
If you want to find two words that are near or further apart then you can add /n (where n is a number or words between the two words):
science NEAR/3 mathematics science NEAR/15 mathematics
More complex queries
You can combine the above three features in various ways:
"supply change management" NEAR business +"supply change management" -science
Xapian has a much more complex query syntax than this but this is not directly available for the simple search web interface (e.g. http://example.eprints.org/cgi/search/simple). However, it would be possible to create a separate search interface (available through a web browser or directly over HTTP without a human-readable web interface) that would allow you do even more specific or complex searches as described at https://xapian.org/docs/queryparser.html.