Perhaps you should try some spelling variations:
the preprocessing » the processing (Expand search), their processing (Expand search), image preprocessing (Expand search)
decrease covid » increase covid (Expand search), increased covid (Expand search), disease covid (Expand search)
covid decrease » rapid decrease (Expand search), soil decrease (Expand search), via decrease (Expand search)
decrease the » decreases the (Expand search), decrease of (Expand search)
decrease not » decrease of (Expand search), decrease akt (Expand search), decrease at (Expand search)
not decrease » to decrease (Expand search), not increase (Expand search), and decrease (Expand search)
in decrease » in decreased (Expand search), on decrease (Expand search), pain decrease (Expand search)

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: (( decrease covid decrease the preprocessing ) OR ( decrease NOT decrease in decrease ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( decrease covid decrease the preprocessing ) OR ( decrease not decrease in decrease ))~".
• Adding a wildcard symbol may retrieve word variants: (( decrease covid decrease the preprocessing ) OR ( decrease not decrease in decrease ))*.