Perhaps you should try some spelling variations:
significant optimization » significant limitation (Expand Search), significant application (Expand Search), significant association (Expand Search)
optimization paths » optimization methods (Expand Search), optimization method (Expand Search), optimization based (Expand Search)
gap decrease » gain decreased (Expand Search), mean decrease (Expand Search), step decrease (Expand Search)
a decrease » _ decrease (Expand Search), _ decreased (Expand Search), _ decreases (Expand Search)

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "(( significant ((gap decrease) OR (a decrease)) ) OR ( significant optimization paths ))~".
• Adding a wildcard symbol may retrieve word variants: (( significant ((gap decrease) OR (a decrease)) ) OR ( significant optimization paths ))*.