You must have heard about the journal impact factor (IF) and its importance. Researchers want their publications in high impact factor journals. Do you know what IF really is? Lets discuss:
Journal Impact Factor is from Journal Citation Report (JCR), a product of Thomson ISI (Institute for Scientific Information). JCR provides quantitative tools for evaluating journals and the IF is one of these. Basically it is a measure of the frequency with which the “average article” in a journal has been cited in a given period of time.
The IF for a journal is calculated based on a three-year period, and can be considered to be the average number of times published papers are cited up to two years after publication. For example, the IF 2011 for a journal would be calculated as follows:

If X = the number of times articles published in 2009-2010 were cited in indexed journals during 2011,
and Y = the number of articles, reviews, proceedings or notes published in 2009-2010
then IF of 2011 for that journal = X/Y
The IF 2010 will be actually published in 2011, because it could not be calculated until all of the 2010 publications had been received. Impact factor 2011 will be published in 2012 and so on. One can view the impact factor of sciencedirect journals like Bioresource Technology from the “about the journal” link of that journal from the http://www.sciencedirect.com