cience Watch examines here the highest-impact journals in selected fields of science over the last decade. On the following page, are tables listing the top 10 journals in 11 main fields, ranked according to citations per paper (with the order determined by each journal’s cites-per-paper score prior to rounding). 

      For these rankings, Science Watch turned to the Thomson ISI web-based evaluation tool ISI Essential Science Indicators (ESI), which tracks publication and citation data over the last 10 years (with updates every two months). The present survey is based on papers published and cited in ISI-indexed journals between January 1, 1992 , and December 31, 2002 .

     ESI defines "papers" as regular scientific articles, review articles, proceedings papers, and research notes. Not counted are letters to the editor, correction notices, and abstracts. The fields in ESI, and in this study, are defined by groupings of ISI-indexed journals, with no journal assigned to more than one field. Of the 22 broad fields included in ESI, 11 are represented here.

     The journal listings in ESI include review journals, but in this analysis Science Watch elected to rank only those journals that do not exclusively feature reviews. Review articles, of course, serve as a convenient citation resource for authors to refer to previous work on a given topic. Such papers, therefore, tend to be highly cited, and this citation advantage extends to review journals.  For this study, Science Watch chose to present journals that primarily publish discovery accounts and other original research.

       These rankings also include only those journals that published continuously during the period under study, January 1992 to December 2002. Newer journals such as Immunity (1994) or Nature Immunology (2000) were excluded from consideration, because calculation of their citations per paper would reflect different time spans and affect their scores. In instances of journals that changed names (e.g., the Netherlands Journal of Sea Research becoming the Journal of Sea Research, or the Journal of Physical Chemistry splitting into "A" and "B" editions after 1997), impact scores were calculated by using combined citation figures for the old and new names.

    In addition to ranking the specialty journals in each field, ESI also assigns individual papers in the multidisciplinary journals Science, Nature, and Proceedings of the National Academy of Sciences of the USA (PNAS), to their respective fields. (This determination is made by an algorithmic examination of the journals within each paper’s cited references, as well as of the journals in which each paper has subsequently been cited.) Thus, in contrast to ISI Journal Citation Reports, which presents impact-factor data for these journals in a single "multidisciplinary" category, ESI permits their performance to be compared against peer journals in many fields.

     Of the multidisciplinary journals included here, Nature makes a particularly strong showing, appearing not only in all 11 rankings, but in either the #1 or #2 spot in each. Science is nearly as impressive, showing up in all the fields except for Pharmacology & Toxicology, and within the top two in all the remaining lists save for Molecular Biology & Genetics, where it ranks third.  PNAS, meanwhile, is far from absent, appearing in all but the Space Science category, and outside the top five only once.

  On the following page, are tables listing the top 10 journals in 11 main fields, ranked according to citations per paper (with the order determined by each journal’s cites-per-paper score prior to rounding).