Perhaps you should try some spelling variations:
imputation techniques » implantation technique, augmentation techniques, segmentation techniques
gradation technique » floatation technique, inhalation technique, truncation technique
based gradation » based evaluation, based prediction
based based » based closed
based no2 » based co, based n

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 imputation techniques ) or ( learning-based based gradation technique ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( learning-based no2 imputation techniques ) OR ( learning-based based gradation technique )).
• Adding a wildcard symbol may retrieve word variants: (( learning-based no2 imputation techniques ) or ( learning-based based gradation technique ))*.