Perhaps you should try some spelling variations:
20th century » 18th century
ref history » reef history, bief history, etf history
11 germany » 1918 germany, 7 germany, 8 germany
11 german » 1 german
20 20th » 90 20th, 2019 20th, 2020 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 %((11 germany) OR (11 german)) %((ref history) OR (((imf history) OR (brief history)))) %20 20th century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %((11 germany) or (11 german)) %((ref history) or (((imf history) OR (brief history)))) %20 20th century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((11 germany) or (11 german)) %((ref history) or (((imf history) OR (brief history)))) %20 20th century%22*.