For citations in chemistry, the American Chemical Society (ACS) style guide is preferred: ACS Style Guide: Effective Communication of Scientific Information. On Reserve at the main desk in Seymour Library, call number: QD8.5 .A25 2006.
For citations in physics, the American Institute of Physics (AIP) Style Manual is recommended (pdf).
For citations in geology and earth sciences, the U.S. Geological Survey has a writing style guide covering many aspects of report writing. See the section "Preparing References for Survey Reports" for guidelines on citing sources.