Perhaps you should try some spelling variations:
20th century » 18th century
ref history » reef history, brief history, bief history
imf history » brief history
21 germany » 11 germany, 2 germany, 20 germany
1990 20th » 1995 20th, 1999 20th, 1994 20th

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: %22agriculture AND state %21 germany %((ref history) OR (imf history)) %1990 20th century%22.
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %21 germany %((ref history) or (imf history)) %1990 20th century%22*.