Perhaps you should try some spelling variations:
mitigation techniques » imputation techniques
reduction techniques » reduction technique, imputation techniques
no2 mitigation » _ mitigation, error mitigation
n reduction » _ reduction, _ prediction, _ production
based no2 » based co
based n » based _, based k, based 3d

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (( learning-based n reduction techniques ) or ( learning-based no2 mitigation techniques ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( learning-based n reduction techniques ) OR ( learning-based no2 mitigation techniques )).
• Adding a wildcard symbol may retrieve word variants: (( learning-based n reduction techniques ) or ( learning-based no2 mitigation techniques ))*.