Perhaps you should try some spelling variations:
9.13 germany » 9.15 germany, 9.16 germany, 113 germany
9.14 germany » 9.15 germany, 9.16 germany, 8.4 germany
ref history » reef history, brief history, bief history
2f 20th » 2.2 20th
20 20th » 90 20th, 2019 20th, 2020 20th

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 %((9.13 germany) OR (9.14 germany)) %ref history %((2f 20th) OR (20 20th)) century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %((9.13 germany) or (9.14 germany)) %ref history %((2f 20th) OR (20 20th)) century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((9.13 germany) or (9.14 germany)) %ref history %((2f 20th) OR (20 20th)) century%22*.