Perhaps you should try some spelling variations:
mitigation techniques » imputation techniques
reduction techniques » reduction technique, imputation techniques
ko2 mitigation » _ mitigation, error mitigation
no2 reduction » h2o2 reduction, _ reduction
based no2 » based co, based n
based ko2 » based co, based k

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 no2 reduction techniques ) OR ( learning-based ko2 mitigation techniques ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( learning-based no2 reduction techniques ) OR ( learning-based ko2 mitigation techniques ))".
• Adding a wildcard symbol may retrieve word variants: (( learning-based no2 reduction techniques ) OR ( learning-based ko2 mitigation techniques ))*.