Perhaps you should try some spelling variations:
9.13 germany » 9.14 germany, 9.15 germany, 9.16 germany
reef history » reeves history, reef fishery
20th century » 18th century
2.1 germany » 21 germany, 2017 germany, 9.14 germany
2f history » 2.1 history, etf history, ref history
2f 20th » 20 20th, 2.2 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 %((2.1 germany) OR (9.13 germany)) %((((2f history) OR (((reef history) OR (brief history))))) OR (imf history)) %2f 20th century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %((2.1 germany) OR (9.13 germany)) %((((2f history) or (((reef history) or (brief history))))) or (imf history)) %2f 20th century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((2.1 germany) OR (9.13 germany)) %((((2f history) or (((reef history) or (brief history))))) or (imf history)) %2f 20th century%22*.