SciFinder (Chemical Abstracts) is a comprehensive tool covering the chemical literature back to 1907, and is used primarily by researchers and advanced students. Caveats: SciFinder requires advance personal registration. Retrieval on simple searches may be overwhelming, since CAS indexes thousands of publications and millions of patents in over 50 languages. Many of these are not readily available to UT users.
Web of Science is a large database that covers thousands of journals across all scientific disciplines. It doesn't require a user account and indexes less foreign language material than SciFinder, so it's a good tool for students new to literature searching. We'll use this database as the example in this tutorial.
Analytical Abstracts is useful for searching across about 50 key analytical science journals since 1980. It's not nearly as comprehensive as SciFinder or Web of Science, but you can define an analyte and matrix, and it's easy to use.