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. 2020 Sep 28;10(9):e037331. doi: 10.1136/bmjopen-2020-037331

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© Author(s) (or their employer(s)) 2020. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

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Proposed flowchart of the literature search process. CBM, Chinese BioMedical Literature Database; CNKI, China National Knowledge Infrastructure; VIP, Chinese Scientific Journal Database.