Perhaps you should try some spelling variations:
ref history » reef history, brief history, bief history
21 germany » 11 germany, 2 germany, 20 germany
12 germany » 11 germany, 12 german, 2 germany
14 germany » 4 germany, 11 germany, 1945 germany
90 20th » 20 20th, 1990 20th
94 20th » 4 20th, 94 24th, 1994 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 (((12 germany) OR (14 germany)))) %ref history %((90 20th) OR (94 20th)) century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %((21 germany) or (((12 germany) OR (14 germany)))) %ref history %((90 20th) or (94 20th)) century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %((21 germany) or (((12 germany) OR (14 germany)))) %ref history %((90 20th) or (94 20th)) century%22*.