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)
"50 ms decrease" » "50 _ decrease" (Expand Search), "50 nn decrease" (Expand Search), "50 mean decrease" (Expand Search), "50 mg decrease" (Expand Search)
"50 mm decrease" » "50 _ decrease" (Expand Search), "50 nn decrease" (Expand Search), "50 we decrease" (Expand Search), "50 mg decrease" (Expand Search), "10 mm decrease" (Expand Search), "20 mm 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 (((((\"50 ms decrease\") OR (\"50 mm decrease\"))) OR (\"50 a decrease\"))))~".
• Removing quotes may allow a broader search: (( 50 ppm decrease ) OR ((((( 50 ms decrease ) OR ( 50 mm decrease ))) OR ( 50 a decrease ))))~.
• Adding a wildcard symbol may retrieve word variants: (("50 ppm decrease") OR ((((("50 ms decrease") OR ("50 mm decrease"))) OR ("50 a decrease"))))*.