Perhaps you should try some spelling variations:
decrease learning » increases learning (Expand search), decreases weaning (Expand search), defense learning (Expand search)
learning effects » learning effect (Expand search), meaning effects (Expand search), learning objects (Expand search)
decrease hiv » decrease in (Expand search), decrease their (Expand search), decreased high (Expand search)
hiv decrease » via decrease (Expand search), hiv increase (Expand search), will decrease (Expand search)
decrease and » decreases and (Expand search), decrease in (Expand search), decrease of (Expand search)
and decrease » and decreases (Expand search), and decreased (Expand search), and increase (Expand search)
decrease can » decrease in (Expand search), decrease at (Expand search), decrease on (Expand search)
can decrease » can increase (Expand search), to decrease (Expand search), the 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 hiv decrease AND decrease ) OR ( decrease can decrease learning effects ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( decrease hiv decrease and decrease ) OR ( decrease can decrease learning effects ))~".
• Adding a wildcard symbol may retrieve word variants: (( decrease hiv decrease and decrease ) OR ( decrease can decrease learning effects ))*.