Perhaps you should try some spelling variations:
ref history » reef history, brief history, bief history
2f history » imf history, etf history, tnf history
2f germany » 2 germany, 20 germany, 21 germany
1990 20th » 1995 20th, 1990 2000, 1990 2010
1999 20th » 1995 20th, 1999 24th, 1999 29th
1994 20th » 1995 20th, 1994 10th, 1994 24th
90 20th » 20 20th, 94 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 %((2f history) OR (ref history)) %((((90 20th) OR (((1990 20th) OR (1999 20th))))) OR (1994 20th)) century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %2f germany %((2f history) or (ref history)) %((((90 20th) or (((1990 20th) OR (1999 20th))))) or (1994 20th)) century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %2f germany %((2f history) or (ref history)) %((((90 20th) or (((1990 20th) OR (1999 20th))))) or (1994 20th)) century%22*.