Perhaps you should try some spelling variations:
20th century » 18th century
ref history » reef history, brief history, bief history
imf history » brief history
1 german » 2 german, 5 german, 7 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 %((((1 german) OR (3 german))y) OR (((1 german) OR (3 german)))) %((ref history) OR (imf history)) %20 20th century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %((((1 german) OR (3 german))y) or (((1 german) OR (3 german)))) %((ref history) or (imf history)) %20 20th century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((((1 german) OR (3 german))y) or (((1 german) OR (3 german)))) %((ref history) or (imf history)) %20 20th century%22*.