What is the difference between Biological Abstracts and BIOSIS Previews? And what is the update rate?

Essentially, they are one and the same. Biological Abstracts started in 1926, long before the age of computer databases. It is now produced by the BioSciences Information Service (=BIOSIS). The online database BIOSIS Previews, describes itself as "the world's most comprehensive reference database for life science research". Biological Abstracts is now its alternative name.

Additionally, to answer your question about the rate of updates to BIOSIS, I contacted the database publisher. Here's their answer:

 "Not totally sure you are asking about when Biosis Previews is updated or the number of articles in each update. As of November 2011, BIOSIS Citation Index and Biosis Previews are updated once per week. The file is usually updated on Friday.

Unfortunately, there are no records kept regarding how many articles are added for each update. One way to check the number of records added for a single update is to go to the Biosis Previews search page. Run any search - topic=cancer - for example. Set Timespan option to current week. Run the search. At the results set scroll down to bottom of page and it will show the number of record the search ran against. This number will be the number of records added in the past update. "

Lastly, BIOSIS database has been acquired by Thomson Reuters, and runs on their platform, where it can now be searched with the other Web of Knowledge indexes (e.g.: Science Citation Index).

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