Perhaps you should try some spelling variations:
christian oboen » christian about, christian onof, christian order
christian boehm » christian both, christian behl, christian beck
reef history » brief history, reeves history, reef fishery
20th century » 18th century
etf history » imf history, tnf history, beruf history
ref history » brief history, bief history, imf history
2 german » 3 german, 5 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: %((christian oboen) OR (christian boehm)) conversations %2 german %((((etf history) OR (reef history))) OR (ref history)) %2f 20th century%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%((christian oboen) or (christian boehm)) conversations %2 german %((((etf history) OR (reef history))) or (ref history)) %2f 20th century%22".
• Adding a wildcard symbol may retrieve word variants: %((christian oboen) or (christian boehm)) conversations %2 german %((((etf history) OR (reef history))) or (ref history)) %2f 20th century%22*.