Perhaps you should try some spelling variations:
ref history » reef history, brief history, bief history
imf history » brief history
21 germany » 11 germany, 2 germany, 20 germany
2f history » etf history, tnf history, 7 history
2019 20th » 2019 4th, 2019 5th, 2019 16th
2019 6th » 2019 4th

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 %((((2f history) OR (ref history))) OR (imf history)) %((2019 20th) OR (2019 6th)) century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %21 germany %((((2f history) or (ref history))) or (imf history)) %((2019 20th) OR (2019 6th)) century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %21 germany %((((2f history) or (ref history))) or (imf history)) %((2019 20th) OR (2019 6th)) century%22*.