Perhaps you should try some spelling variations:
ref history » reef history, brief history, bief history
2f history » imf history, etf history, tnf history
21 germany » 11 germany, 2 germany, 20 germany
2019 20th » 2019 4th, 2019 6th, 2019 5th
90 20th » 1990 20th
94 20th » 4 20th, 94 24th, 1994 20th
20 20th » 2020 20th, 2023 20th, 2021 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 %((2f history) OR (ref history)) %((((20 20th) OR (2019 20th))) OR (((90 20th) OR (94 20th)))) 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)) %((((20 20th) or (2019 20th))) or (((90 20th) or (94 20th)))) century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %21 germany %((2f history) OR (ref history)) %((((20 20th) or (2019 20th))) or (((90 20th) or (94 20th)))) century%22*.