Perhaps you should try some spelling variations:
"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), "50 nsg decrease" (Expand Search), "50 μg decrease" (Expand Search), "50 _g 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)
"50 n decrease" » "50 nn decrease" (Expand Search), "50 _ decrease" (Expand Search), "50 _ decreased" (Expand Search), "50 ns decrease" (Expand Search), "50 μ decrease" (Expand Search)

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