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 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 ng decrease" » "50 nn decrease" (Expand Search), "50 _ decrease" (Expand Search), "50 we decrease" (Expand Search), "50 mg decrease" (Expand Search), "10 ng decrease" (Expand Search), "5 ng decrease" (Expand Search)
"5 a decrease" » "5 _ decrease" (Expand Search), "5 _ decreased" (Expand Search), "5 _ 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: "((((\"50 ppm decrease\") OR (((\"5 a decrease\") OR (\"5 nm decrease\"))))) OR (\"50 ng decrease\"))~".
• Removing quotes may allow a broader search: (((( 50 ppm decrease ) OR ((( 5 a decrease ) OR ( 5 nm decrease ))))) OR ( 50 ng decrease ))~.
• Adding a wildcard symbol may retrieve word variants: (((("50 ppm decrease") OR ((("5 a decrease") OR ("5 nm decrease"))))) OR ("50 ng decrease"))*.