Perhaps you should try some spelling variations:
20th century » 18th century
2.1 germany » 2017 germany, 9.13 germany, 9.14 germany
ref history » reef history, bief history, etf history
21 germany » 11 germany, 2 germany, 20 germany
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 (2.1 germany)) %((((ref history) OR (brief history))) OR (imf history)) %20 20th century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %((21 germany) OR (2.1 germany)) %((((ref history) or (brief history))) or (imf history)) %20 20th century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((21 germany) OR (2.1 germany)) %((((ref history) or (brief history))) or (imf history)) %20 20th century%22*.