Science Watch now presents an updated collection of journal rankings, based on a special subset of Essential Science Indicators (ESI) data covering the last six years, reflecting papers published and cited in Thomson-indexed journals between January 1999 and August 2004. Below, are tables listing the top 10 journals in 11 main fields, ranked by impact (the order is determined by each journal’s cites-per-paper score prior to rounding).

This survey, like its predecessor, adheres to the ESI definition of "papers" as regular scientific articles, review articles, proceedings papers, and research notes. Letters to the editor are excluded, as are correction notices and abstracts. The fields covered in ESI (22 in all, half of which are represented here) are defined by groupings of Thomson-indexed journals, with no journal assigned to more than one field.

As was the case last time, Science Watch elected to scrutinize the ESI journal rankings and leave out those journals that exclusively publish review articles. Reviews, of course, as convenient summaries of past research, tend to be highly cited—as is the case, subsequently, with review journals. The present rankings reflect journals that primarily publish discovery accounts and other original research.

The rankings are also confined to journals that published continuously during the six-year period, from January 1999 to August 2004. To ensure that all journals were assessed over the same time span, such journals as Nature Immunology, which began publication in 2000, or Cancer Cell, which dates from 2002, were excluded. In the case of journals that underwent a name change during the period under study (for example, American Zoologist, which became Integrative and Comparative Biology in 2002), impact scores were calculated by combining the publication and citation figures for the old and new names.

ESI, as noted in the previous survey, not only lists the specialty journals in each field but can also assign papers from the multidisciplinary journals Nature, Science, and Proceedings of the National Academy of Sciences of the USA (PNAS) to the proper field (based on an algorithmic assessment of each paper’s cited references, as well as of the journals in which each paper has subsequently been cited).

In all 11 of the fields shown here, Nature and Science obviously predominate, with both appearing at either #1 or #2 in each field (although Science claims the slight majority with six #1 showings). In a few instances, as the rounded figures show, the results were virtually identical (in Space Science, for example, where Science squeaked by with 24.06 cites per paper, compared to Nature’s mark of 23.86). PNAS was also in the thick of things, appearing in nine of the rankings, and within the top five in seven.