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. 2011 Jun 23;4:18. doi: 10.1186/1756-0381-4-18

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Copyright ©2011 Zheng et al; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Graphics of the first discrete derivative based on frequency with nodes in parenthesis. These networks are constructed with data set downloaded from PubMed on May 9, 2010. They are built under the conditions that for a network on frequency i (i = 1, 2, 3,,···, 29) which are in Fig. 8. We calculate the discrete derivative with i ≤ 28.

Inline graphic — Graphics of the first discrete derivative based on frequency with nodes in parenthesis. These networks are constructed with data set downloaded from PubMed on May 9, 2010. They are built under the conditions that for a network on frequency i (i = 1, 2, 3,,···, 29) which are in Fig. 8. We calculate the discrete derivative with i ≤ 28.