被引半衰期 (Cited Half-life)，显示一份期刊从当前年度向前推算引用数占截止当前年度被引用期刊的总引用数50%的年数，是测度期刊老化速度的一种指标。 半衰期通常不是针对个别文献或某一组文献，而是指某一学科或专业领域的文献总和而言的。

研究型期刊被引半衰期相对长，时效性期刊被引半衰期相对短。

Journal Cited Half-Life

The median age of the articles that were cited in the JCR year. Half of a journal's cited articles were published more recently than the cited half-life. For example, in JCR 2001 the journal Crystal Research and Technology has a cited half-life of 7.0. That means that articles published in Crystal Research and Technology between 1995-2001 (inclusive) account for 50% of all citations to articles from that journal in 2001.

Only journals cited 100 or more times in the JCR year have a cited half-life.

A higher or lower cited half-life does not imply any particular value for a journal. For instance, a primary research journal might have a longer cited half-life than a journal that provides rapid communication of current information. Cited half-life figures may be useful to assist in collection management and archiving decisions. Dramatic changes in cited half-life over time may indicate a change in a journals format. Studying the half-life data of the journals in a comparative study may indicate differences in format and publication history.

Aggregate Cited Half-Life

The aggregate cited half-life is calculated the same way as the journal cited half-life, and its significance is comparable. For both journals and subject categories, the cited half-life is the median age of the articles that were cited in the JCR year. The aggregate cited half-life is an indication of the turnover rate of the body of work on a subject.

For example, in JCR 2003 the subject category Energy & Fuels has a cited half-life of 7.0. That means that articles published in Energy & Fuels journals between 1997-2003 (inclusive) account for 50% of all citations to articles from those journals in 2003.

引用半衰期（CitingHalf Life）：计算某一期刊平均引用多久以前的论文。计算方法是将该期刊当年所发表论文之所有（本资料库内收录）期刊论文类引文，依据出版年份之篇数由当年往前累计，当引用的论文篇数累计达到全部的50%时，该篇论文的出版年到当年的间隔年数即為此一期刊的引用半衰期。半衰期的值越低，表示该期刊所引用之参考文献时效性越高。

Journal Citing Half-Life

The citing half-life is the median age of articles cited by the journal in the JCR year. For example, in JCR 2003, the journal Food Biotechnology has a citing half-life of 9.0. That means that 50% of all articles cited by articles in Food Biotechnology in 2003 were published between 1995 and 2003 (inclusive).

Only journals that publish 100 or more cited references have a citing half-life. Cited-only journals do not have a citing half-life.

Aggregate Citing Half-Life

The aggregate citing half-life is calculated the same way as the journal citing half-life, and its significance is comparable. For a subject category, the citing half-life is the median age of articles cited by journal in the category in the JCR year.

For example, in JCR 2003, the subject category Geochemistry & Geophysics has a citing half-life of 9.9. That means that 50% of all articles cited by articles in Geochemistry & Geophysics journals in 2003 were published between 1994 and 2003 (inclusive).