Perhaps you should try some spelling variations:
20th century » 18th century
ref history » reef history, brief history, bief history
etf history » reef history, imf history, tnf history
2f germany » 2 germany, 20 germany, 21 germany
2f history » 2.1 history, imf history, tnf history
1 german » 3 german, 5 german, 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 (1 german)) %((((2f history) OR (ref history))) OR (etf history)) %2f 20th century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %((2f germany) or (1 german)) %((((2f history) OR (ref history))) or (etf history)) %2f 20th century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((2f germany) or (1 german)) %((((2f history) OR (ref history))) or (etf history)) %2f 20th century%22*.