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, brief history, bief history
imf history » brief history
21 germany » 11 germany, 2 germany, 20 germany
2f history » 2.1 history, etf history, tnf history
90 20th » 20 20th, 94 20th, 1990 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)) %((((2f history) OR (ref history))) OR (imf history)) %90 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)) %((((2f history) or (ref history))) or (imf history)) %90 20th century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((21 germany) OR (2.1 germany)) %((((2f history) or (ref history))) or (imf history)) %90 20th century%22*.