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, 8 germany
2019 20th » 2019 4th, 2019 6th, 2019 5th
2 german » 3 german, 5 german
20 20th » 90 20th, 2020 20th, 2023 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) OR (2 german)))) %ref history %((20 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) OR (2 german)))) %ref history %((20 20th) or (2019 20th)) century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((21 germany) or (((2 germany) OR (2 german)))) %ref history %((20 20th) or (2019 20th)) century%22*.