Perhaps you should try some spelling variations:
20th century » 18th century
ref history » reef history, brief history, bief history
2f germany » 20 germany, 25 germany, 26 germany
21 germany » 2.1 germany, 11 germany, 20 germany
2f history » imf history, etf history, tnf history
2 germany » 12 germany, 7 germany, 2 german
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 %((2f germany) OR (((21 germany) OR (2 germany)))) %((2f history) OR (ref history)) %2f 20th century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %((2f germany) or (((21 germany) OR (2 germany)))) %((2f history) or (ref history)) %2f 20th century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((2f germany) or (((21 germany) OR (2 germany)))) %((2f history) or (ref history)) %2f 20th century%22*.