Perhaps you should try some spelling variations:
20th century » 18th century
ref history » reef history, brief history, bief history
21 germany » 2 germany, 20 germany, 7 germany
11 germany » 1918 germany, 7 germany, 8 germany
2f history » imf history, etf history, tnf history
11 german » 1 german
2 german » 3 german, 5 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 %((((21 germany) OR (((11 germany) OR (11 german))))) OR (2 german)) %((2f history) OR (ref history)) %20 20th century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %((((21 germany) or (((11 germany) or (11 german))))) or (2 german)) %((2f history) OR (ref history)) %20 20th century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((((21 germany) or (((11 germany) or (11 german))))) or (2 german)) %((2f history) OR (ref history)) %20 20th century%22*.