Funding for this research was provided by:
National Institute on Drug Abuse (K23DA040923)
National Institutes of Health (UL1TR001082)
Received: 13 December 2017
Accepted: 19 June 2018
First Online: 5 July 2018
Ethics approval and consent to participate
: Not applicable. This was an observational bibliometric study.
: Not applicable
: The authors declare that they have no competing interests.
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