Perhaps you should try some spelling variations:
"learning-based co imputation techniques" » "learning-based co implantation technique", "learning-based co augmentation techniques", "learning-based co segmentation techniques", "learning-based co limitation techniques", "learning-based code imputation techniques", "learning-based no2 imputation techniques", "learning-based two imputation techniques"
"learning-based 3d inhaler technique" » "learning-based 3d inhalation technique", "learning-based _ inhaler technique", "learning-based k inhaler technique", "learning-based n inhaler technique"

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 co imputation techniques") or ("learning-based 3d inhaler technique"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("learning-based co imputation techniques") OR ("learning-based 3d inhaler technique")).
• Removing quotes may allow a broader search: (( learning-based co imputation techniques ) or ( learning-based 3d inhaler technique )).
• Adding a wildcard symbol may retrieve word variants: (("learning-based co imputation techniques") or ("learning-based 3d inhaler technique"))*.