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. 2018 Dec 14;12(Suppl 7):116. doi: 10.1186/s12918-018-0640-4

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© The Author(s). 2018

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Fig. 7 — Research hotspots of every year from 2007 to 2016 are summarized in this figure. The words which appear more than thrice are marked by red, those appear thrice are marked by orange, those appear twice are marked by blue, and those appear only once are marked by black. (Adapted with permission from [44])