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