Perhaps you should try some spelling variations:
_ functionalanalysis » der funktionalanalysis, die funktionalanalysis, und funktionalanalysis
functional » function, functions
functionalanalysis » functionanalysis, functionsanalysis

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: %((functional analysis) OR (_ functionalanalysis))%22*.