At first glance, it seems like a nerdier version of Facebook. There's the profile picture, the list of interests, the space for your Web site. Most of the members have Ph.D.'s, though, and instead of posting party invites or YouTube videos, their "Recent Activity" is full of academic papers and scholarly treatises.

Welcome to CiteULike, a social bookmarking tool that allows users to post, share and comment on each other's links -- in this case, citations to journal articles with titles like "Trend detection through temporal link analysis" and "The Social Psychology of Inter- and Intragroup Conflict in Governmental Politics." It's a sort of "del.icio.us for academics," said Kevin Emamy, a representative for the site's London-based holding company, Oversity Ltd. It started out as a personal Web project in 2004 and grew organically by word of mouth. Today, it has some 70,000 registered users and a million page views a month, he said.

Like other similar sites, CiteULike allows users to register, create profiles and submit links that others can read, comment on, tag with relevant keywords and in turn share again. Moving away from the card-catalog view of scholarship, in which researchers dig through archives of recent and not-so-recent journal databases in sequence, the "social discovery" model, as Emamy describes it, allows colleagues to learn from each other's bookmarks and potentially collaborate in groups.

"Using a tool like CiteULike, researchers (who are finding 99 percent of their journal papers online, probably bypassing the library) can now reach directly into the bookshelves of other researchers in their field (or any other field), anywhere the world, knowing nothing about them other than what they have bookmarked, and see what they are reading right now," he said.

One could almost describe it as looking over your neighbor's shoulder in the library -- except in this case everything is public to begin with. The site lists citations only, not the full text, and links to journal databases -- most of which require a subscription, such as from a university library -- for access to the articles. JSTOR, HighWire Press and other major online repositories are represented, allowing relatively seamless integration between CiteULike references and the articles they link to, as long as the user is on a computer account covered by a subscription. (JSTOR declined to comment about its partnership with the site.)

A browser button allows researchers to instantly flag a journal article for online bookmarking, and the site automatically extracts the citation information from the Web page. (In the spirit of open source, users can write their own plugins to make the site compatible with other databases.) The result is an online repository of citations for personal use -- a bibliography of sorts -- as well as a larger snapshot of what friends and colleagues are reading. Scholars can also upload PDF files of papers they have downloaded, but they are kept private, like a personal online flash drive.

Alternatively, some sites, like Science online, place links on each article page that automatically create bookmarks on users' CiteULike accounts. (For example, click here to post this article to del.icio.us.)

"We thought they were sort of an ideal social bookmarking service for that kind of thing," said Stewart Wills, the journal's online editor. "We think it’s sort of a nice way to add a social bookmarking component that is relevant to the kind of people who are using our content."

Wills added that such links -- and their potential to boost awareness of the publication's content in a more organic way -- are a conscious part of its strategy. "We are definitely looking at this space very carefully and are interested in expanding, and this is one step in that expansion," he said.

Already, the space is growing. CiteULike offers services similar to what's being promised in the next iteration of Zotero, an open-source browser plugin that lets researchers collect and organize sources, including articles, Web pages, files and other media. The developers promise a new version with more collaborative and resource-sharing capabilities. Connotea, from Nature Publishing Group, offers a more science-oriented version of CiteULike, while RefWorks -- which, unlike the others, is not free and was recently acquired by ProQuest -- is intended for larger-scale applications. (Another entry is Thomson's EndNote.)

"CiteULike is a real pioneer, I think," said Dan Cohen, the director of the Center for History and New Media at George Mason University, which created Zotero. Cohen noted that on Thursday -- this morning -- he had a conference call scheduled with CiteULike to "explore ways to work together," such as the ability to import and export citations between the two interfaces.

The eventual goal, he said, is “the seamless transfer of scholarly resources wherever they may lie” -- demonstrated recently by Zotero's announcement that it was teaming up with the Internet Archive to allow scholars to delve into their hard drives and optically scan their documents for the public domain.