In recent years, the extremely limited value of traditional indexes for substructure searching has become well recognized. As a result, considerable research effort has been financed for substructure search systems. However, with few exceptions, this research effort has been aimed at developing computer systems, even though most chemists do not have immediate access to computers. Manual substructure searches remain laborious or impossible to perform. The development of "desk-top" manually search-* To whom inquiries should be addressed. able indexes by permuting line notations was first reported in 1963.1 These indexes permit manual substructure searching that is impossible or impractical with traditional manual indexes such as the subject or formula indexes to Chemical Abstracts, Index Chemicus, or Beilstein. Various versions of permuted line notation indexes are now used by many large organizations for internal files. However, access to the open literature for the chemist interested in finding new compounds that contain a particular substructure was unachievable prior to the introduction of the Chemical Substructure Index (CSI).
The Index Chemicus Registry System (ICRS), launched in 1968 with the support of a dozen industrial and government organizations, is now a current operational monthly service. Subscribers receive magnetic tapes and printouts, in which the weekly issues of Index Chemicus (IC) have been encoded in Wiswesser Line Notations (WLN). Over 13,000 compounds per month are provided in machine language. The canonical WLN is also provided in alphabetized printouts. Encoding of over 400,000 new chemical compounds from IC has already been completed, including all those reported in 1967, 1968, and 1969. Since the tapes also include title and other bibliographic information, this paper describes the use of supporting software provided for SOI search systems employing "word" and other searching terms, in addition to the WLN fragments. Use of the monthly and annual printouts are illustrated for those searches which do not require computer manipulation.
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