@article{Shannon1948, author = "C. E. Shannon", title = "{A Mathematical Theory of Communication}", journal = "Bell System Tech. J.", volume = "27", pages = "379--423, 623--656", note = "\htmladdnormallink {http://dx.doi.org/10.1002/j.1538-7305.1948.tb01338.x} {http://dx.doi.org/10.1002/j.1538-7305.1948.tb01338.x}", comment = "\htmladdnormallink {http://cm.bell-labs.com/cm/ms/what/shannonday/paper.html} {http://cm.bell-labs.com/cm/ms/what/shannonday/paper.html} this breaks at the '-'., \htmladdnormallink {http://tinyurl.com/Shannon1948} {http://tinyurl.com/Shannon1948}, 2016 Jan 14: http://tinyurl.com/Shannon1948 which pointed to http://cm.bell-labs.com/cm/ms/what/shannonday/paper.html is now broken. http://cm.bell-labs.com/ says: This used to be home of the Computing Science Research Center, but following the reorganization of Bell Labs in October 2005, the new home of computing and mathematics is at www.bell-labs.com. Problems/complaints/comments to webmaster@plan9.bell-labs.com. --- 2016 Apr 21 google: C. E. Shannon A Mathematical Theory of Communication https://www.google.com/search?&q=C.+E.+Shannon+A+Mathematical+Theory+of+Communication gave: https://www.math.bgu.ac.il/~yairgl/teaching/codes/shannon.pdf But 10.1002/j.1538-7305.1948.tb01338.x is better.", year = "1948"}

Unfortunately the version kept at Bell Labs is gone.
You could try this google search to find a copy:

google:

shannon 1948