Perhaps you should try some spelling variations:
ref history » reef history, brief history, bief history
21 germany » 2.1 germany, 11 germany, 2 germany
20 germany » 2 germany, 7 germany, 8 germany
20 20th » 90 20th, 2019 20th, 2020 20th
94 20th » 4 20th, 90 20th, 94 24th

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 (20 germany)) %ref history %((20 20th) OR (94 20th)) century%22.
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((21 germany) or (20 germany)) %ref history %((20 20th) or (94 20th)) century%22*.