searches a specific subset of Google's index and covers a wide swath of fields, from medicine and physics to economics and computer science.
Search algorithms also are specially tailored for the new service, said Anurag Acharya, a principal engineer at Google.
The free service will not initially carry Web search advertisements, Acharya said. Web search advertising accounts for almost all of Google's revenue, which was $805.9 million in the third quarter.
Shares of Google, which debuted at $85 in mid-August, closed at $172.50 on Nasdaq on Wednesday.