A few personal favorites from the list of alternatives to the popular Web of Science (WoS) index reviewed by Dana L. Roth (for details, see the RMIMR post or the full PDF file). In accordance with my personal research interests, these are the tools useful for literature and citation searches in Physics and Chemistry.
Web of Science
WoS and other databases from Thomson Scientific like ISI Web of Knowledge and the ISI journal impact factor are the tools that I personally use the most. One feature in WoS that I find increasingly useful is the system of citation alerts, whereby I am notified (by e-mail) every time a particular paper has been cited. By selectively “tagging” in this manner several important and specialized papers in a given field (e.g., immobilization of DNA on surfaces), the resulting alerts effectively notify me about most of the new papers on the subject. WoS also happens to provide the easiest way I know to check a Hirsch index.
Google Scholar
In a previous post I already mentioned the updated recent articles option, which attempts to enhance the relevance of the search results. Also very useful are direct links to PDF files of the papers hosted on authors’ websites, in addition to the publishers’ versions, of course.
Search results are displayed according to relevance based on the full text of each article, the article’s author, the publication source and how often it has been cited. Google Scholar also automatically analyses and extracts citations and presents them as separate results, even if the documents they refer to are not online.
Chemical Abstracts/SciFinder/SciFinder Scholar
Many chemists prefer SciFinder over WoS for searches in Chemistry journals, which is not surprising, because SciFinder is based on Chemical Abstracts (CA). On several occasions, SciFinder indeed helped me to find useful references on topics not covered by WoS, but in general the features are very similar between these two major subscription-based services.
[The ‘Get Citing References’] feature is similar to the ‘Times Cited’ link appearing on the full record for individual articles in WoS, which retrieves ‘exact’ citation matches but not citations with minor errors. There are some examples (J. Chem. Soc. Chem. Commun./Chem. Commun.) where citations in CA are algorithmically corrected. In contrast with CA, WoS also indexes articles from journals published in non-Roman alphabets which, by definition, are excluded from the CAplus file.
Scopus and Scirus
Scopus is a comprehensive subscription-based indexing service from Elsevier, which directly competes against SciFinder and WoS. Scirus, is the often-overlooked free version of the same index. Perhaps the most unique functionality of Scirus is an automatically-generated list of suggested search refinements, based on keyword frequency in the current set of results. This is a very convenient option for initial broad searches on an unfamiliar topic, because it helps to quickly identify the relevant search terms. Oddly enough, this option is only offered in Scirus, but not in Scopus. Update: see a more extended discussion of the differences between Scopus and Scirus in the comments to this post.
Scopus is a ‘work in progress’ that is based on a variety of sources which result in some interesting retrievals. A ‘Basic’ search for Marcus, R. A. as an author retrieves 56 items including an article authored by Marcus A. R. Several articles are listed twice, suggesting incomplete editing of overlapping sources for the article references. The results list displays the article title, authors source and the number of ‘cited by’ references in the
Scopus database.
CiteSeer
CiteSeer is, perhaps, the most Web 2.0 tool from the list, with a lot of useful features, like citation analysis and direct links to PDFs. Unfortunately, it only indexes computer and information science literature. So for now I can only hope that a similar index will be created for other sciences, or at least some of the features will be adopted by the existing indices.
biohacker 
Hi,
nice reading. Just one point. Scirus is NOT the free version of Scopus. Scopus is the comprehensive A&I service for STM indexing some 16000 journals, partly back to 1996, partly back to 1965, with full citation analysis options. It includes almost completely the subject index Compendex, Geobase, Biobase and Embase.
The free Scirus database, also made by Elsevier, only has journal information for Elsevier Journals and federates information from ArXiv, Pubmed and other free datbases. Scirus adds to that a search function for a selected slice of the free web: some 300 million general webpages in science.
The Scopus database does have a tab to search the free web part of Scirus.
Thanks for the correction, Jeroen! I personally have been using Scirus for about five years, and Scopus only for the last two, so I always thought about Scopus as a more sophisticated (and hence not free) version of Scirus. I was not aware, however, of the substantial difference between the underlying databases that you mentioned, in part because for my searches on Surface Science topics, there was little apparent difference between the two.
And on the refined search option from Scirus – I actually have asked Elsevier reps a year ago why it wasn’t implemented in the same way for full Scopus searches, only to discover that they didn’t know what I was talking about – these particular two reps didn’t even know about Scirus!
http://scienceworld.wolfram.com/
http://www.doaj.org/
These are pretty good sites
Thanks for the links, Heidi!
For the benefit of the readers who are not familiar with these sites, I should point out that these sites are not search engines for research publications, although both provide free access to science information. ScienceWorld is an on-line science encyclopedia. DOAJ is the Directory of Open Access Journals, which includes a basic search option for the participating journals.