Perhaps you should try some spelling variations:
"50 ppm decrease" » "50 _ decrease" (Expand Search)
"5 ng decrease" » "5 _ decrease" (Expand Search), "5 g decrease" (Expand Search), "5 μg decrease" (Expand Search)
"5 a decrease" » "5 _ decrease" (Expand Search), "5 _ decreased" (Expand Search), "5 _ decreases" (Expand Search)
"5 c decrease" » "5 _ decrease" (Expand Search), "5 _ decreased" (Expand Search), "5 _ decreases" (Expand Search), "45 c decrease" (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: "((\"50 ppm decrease\") OR (((((\"5 ng decrease\") OR (\"5 a decrease\"))) OR (\"5 c decrease\"))))~".
• Removing quotes may allow a broader search: (( 50 ppm decrease ) OR ((((( 5 ng decrease ) OR ( 5 a decrease ))) OR ( 5 c decrease ))))~.
• Adding a wildcard symbol may retrieve word variants: (("50 ppm decrease") OR ((((("5 ng decrease") OR ("5 a decrease"))) OR ("5 c decrease"))))*.