Perhaps you should try some spelling variations:
ref history » reef history, brief history, bief history
21 germany » 11 germany, 2 germany, 20 germany
2023 20th » 2023 26th, 2023 10th, 2020 20th
90 20th » 20 20th, 1990 20th
94 20th » 1994 20th
94 24th » 94 4th, 94 14th, 24 24th
4 20th » _ 20th, a 20th, 1 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 %ref history %((2023 20th) OR (((90 20th) OR (((((94 20th) OR (4 20th))) OR (94 24th)))))) century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %21 germany %ref history %((2023 20th) or (((90 20th) or (((((94 20th) OR (4 20th))) or (94 24th)))))) century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %21 germany %ref history %((2023 20th) or (((90 20th) or (((((94 20th) OR (4 20th))) or (94 24th)))))) century%22*.