Perhaps you should try some spelling variations:
ref history » reef history, brief history, bief history
11 germany » 11 german, 1918 germany, 7 germany
1990 20th » 1995 20th, 1999 20th, 1994 20th
90 20th » 20 20th, 94 20th

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 %11 germany %ref history %((90 20th) OR (1990 20th)) century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %11 germany %ref history %((90 20th) OR (1990 20th)) century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %11 germany %ref history %((90 20th) OR (1990 20th)) century%22*.