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)
"10 ng decrease" » "10 _ decrease" (Expand Search), "10 a decrease" (Expand Search), "10 we decrease" (Expand Search), "100 ng decrease" (Expand Search), "10 mg decrease" (Expand Search), "10 nm decrease" (Expand Search)

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("50 ppm decrease") OR ((("50 nn decrease") OR ("10 ng decrease"))))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"50 ppm decrease\") OR (((\"50 nn decrease\") OR (\"10 ng decrease\"))))".
• Removing quotes may allow a broader search: (( 50 ppm decrease ) OR ((( 50 nn decrease ) OR ( 10 ng decrease )))).
• Adding a wildcard symbol may retrieve word variants: (("50 ppm decrease") OR ((("50 nn decrease") OR ("10 ng decrease"))))*.