Perhaps you should try some spelling variations:
ref history » reef history, brief history, bief history
2.1 germany » 21 germany, 2017 germany, 9.13 germany
20 germany » 2 germany, 8 germany, 5 germany
2f history » imf history, etf history, tnf history
2020 20th » 2020 16th, 2020 2021, 2020 5th
2019 20th » 2019 4th, 2019 6th, 2019 5th
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 %((2.1 germany) OR (((20 germany) OR (7 germany)))) %((2f history) OR (ref history)) %((((2020 20th) OR (2019 20th))) OR (90 20th)) century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %((2.1 germany) or (((20 germany) or (7 germany)))) %((2f history) OR (ref history)) %((((2020 20th) or (2019 20th))) or (90 20th)) century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((2.1 germany) or (((20 germany) or (7 germany)))) %((2f history) OR (ref history)) %((((2020 20th) or (2019 20th))) or (90 20th)) century%22*.