Perhaps you should try some spelling variations:
20th century » 18th century
reef history » reeves history, reef fishery
tnf history » etf history, motif history, stone history
ref history » bief history, etf history, reform history
2f history » etf history, 7 history, bief history
11 germany » 11 german, 1918 germany, 7 germany
21 germany » 2 germany, 20 germany, 7 germany
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 %((21 germany) OR (11 germany)) %((((2f history) OR (((((((ref history) OR (tnf 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 %((21 germany) or (11 germany)) %((((2f history) or (((((((ref history) OR (tnf 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 %((21 germany) or (11 germany)) %((((2f history) or (((((((ref history) OR (tnf history))) or (reef history))) or (brief history))))) or (imf history)) %2f 20th century%22*.