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 nn decrease" » "5 _ decrease" (Expand Search), "k nn decrease" (Expand Search), "_ nn decrease" (Expand Search)
"5 mg decrease" » "5 _ decrease" (Expand Search), "25 mg decrease" (Expand Search), "_ mg decrease" (Expand Search), "5 g 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 nn decrease\"))) OR (\"5 mg decrease\"))))~".
• Removing quotes may allow a broader search: (( 50 ppm decrease ) OR ((((( 5 ng decrease ) OR ( 5 nn decrease ))) OR ( 5 mg decrease ))))~.
• Adding a wildcard symbol may retrieve word variants: (("50 ppm decrease") OR ((((("5 ng decrease") OR ("5 nn decrease"))) OR ("5 mg decrease"))))*.