Perhaps you should try some spelling variations:
"50 ppm decrease" » "50 _ decrease" (Expand Search), "50 nn decrease" (Expand Search), "50 pa decreased" (Expand Search), "5 ppm decrease" (Expand Search)
"5 ng decrease" » "5 nn decrease" (Expand Search), "5 _ decrease" (Expand Search), "5 we decrease" (Expand Search), "5 mg decrease" (Expand Search), "5 g decrease" (Expand Search), "5 kg decrease" (Expand Search)
"5 nm decrease" » "5 nn decrease" (Expand Search), "5 _ decrease" (Expand Search), "5 we decrease" (Expand Search), "5 mm decrease" (Expand Search), "5 cm decrease" (Expand Search)
"50 a decrease" » "50 _ decrease" (Expand Search), "50 _ decreased" (Expand Search), "50 _ decreases" (Expand Search), "50 μ decrease" (Expand Search), "50 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 nm decrease\"))) OR (\"50 a decrease\"))))~".
• Removing quotes may allow a broader search: (( 50 ppm decrease ) OR ((((( 5 ng decrease ) OR ( 5 nm decrease ))) OR ( 50 a decrease ))))~.
• Adding a wildcard symbol may retrieve word variants: (("50 ppm decrease") OR ((((("5 ng decrease") OR ("5 nm decrease"))) OR ("50 a decrease"))))*.