Perhaps you should try some spelling variations:
"50 ppm decrease" » "50 a decrease" (Expand Search), "50 nn decrease" (Expand Search), "50 pa decreased" (Expand Search), "5 ppm decrease" (Expand Search)
"50 n decrease" » "50 nn decrease" (Expand Search), "50 a decrease" (Expand Search), "50 _ decreased" (Expand Search), "50 ns decrease" (Expand Search), "50 ng decrease" (Expand Search), "50 μ decrease" (Expand Search)
"50 c decrease" » "50 c decreased" (Expand Search), "50 a decrease" (Expand Search), "50 rc decreased" (Expand Search), "5 c decrease" (Expand Search), "50 μ decrease" (Expand Search), "20 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 _ decrease\") OR (\"50 n decrease\"))))) OR (\"50 c decrease\"))~".
• Removing quotes may allow a broader search: (((( 50 ppm decrease ) OR ((( 50 _ decrease ) OR ( 50 n decrease ))))) OR ( 50 c decrease ))~.
• Adding a wildcard symbol may retrieve word variants: (((("50 ppm decrease") OR ((("50 _ decrease") OR ("50 n decrease"))))) OR ("50 c decrease"))*.