[27] Periodicals Available online

Use the Journal Article reference type for online articles.

[27] T. Brauner, O. Taanila, A. Tranberg, et al., "Temperature dependence of standard model CP violation," Physical Review Letters, vol. 108, no. 4, DOI:10.1103/PhysRevLett.108.041601, 2012. Available http://prl.aps.org/abstract/PRL/v108/i4/e041601.

1. Use DOI for the digital object identifier. Sometimes the DOI is all numbers and sometimes its an alpha/numeric.