Perhaps you should try some spelling variations:
ref history » reef history, brief history, bief history
21 germany » 2.1 germany, 11 germany, 20 germany
2 germany » 12 germany, 7 germany, 2 german
2023 20th » 2023 26th, 2023 10th, 2020 20th
2019 20th » 2019 4th, 2019 6th, 2019 5th
20 20th » 90 20th, 2020 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) OR (2 germany)) %ref history %((((20 20th) OR (2023 20th))) OR (2019 20th)) century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %((21 germany) or (2 germany)) %ref history %((((20 20th) OR (2023 20th))) or (2019 20th)) century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((21 germany) or (2 germany)) %ref history %((((20 20th) OR (2023 20th))) or (2019 20th)) century%22*.