Open access is being offered to the following article published online today in the Early Edition of the Proceedings of the National Academy of Science:

Rafael Navarro-González, et al.
The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results
PNAS published October 23, 2006, 10.1073/pnas.0604210103
Abstract
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Supporting Text