Perhaps you should try some spelling variations:
ref history » reef history, brief history, bief history
imf history » brief history
21 germany » 2.1 germany, 11 germany, 2 germany
2018 18th » 2018 14th, 2018 10th, 2017 18th

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 %((ref history) OR (imf history)) %((2018 18th) OR (2018 15th)) century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22agriculture and state %21 germany %((ref history) or (imf history)) %((2018 18th) OR (2018 15th)) century%22".
• Adding a wildcard symbol may retrieve word variants: %22agriculture and state %21 germany %((ref history) or (imf history)) %((2018 18th) OR (2018 15th)) century%22*.