| Topic | Papers in top 200 | Average citations | Weighted score | |
| 1 | WAMP observations | 2 | 421 | +554 |
| 2 | Prostate cancer | 4 | 88 | +293 |
| 3 | Clopidogrel | 3 | 78 | +260 |
| 4 | Type-2 diabetes | 4 | 77 | +257 |
| 5 | H1N1 virus | 4 | 59 | +197 |
| 6 | Iron-based superconductors | 6 | 43 | +172 |
| 7 | Anti-angiogenesis cancer therapy | 2 | 51 | +170 |
| 8 | Graphene | 6 | 38 | +152 |
| 9 | Small RNAs | 3 | 73 | +133 |
| 10 | Obesity | 6 | 39 | +130 |
| 11 | Induced pluripotent stem cells | 6 | 44 | +80 |
| 12 | Inflammasome | 3 | +56 |
The topics are ranked by comparing the average number of citations with the average score for the field of the topic.
Naturally, a majority of the papers identified were published in the first half of 2009, since those published later in the year had little time to collect citations. Therefore, the summary represents a snapshot focusing on the first part of 2009 and represents early returns. Despite this qualification, the topics highlighted continued to be represented in papers published and citations received to the end of the year.
By far the most influential in terms of citation clout were two reports dealing with the five-year observations from the Wilkinson Anisotropy Microwave Probe (WAMP). As Science Watch correspondent Simon Mitton notes: “WAMP is of central importance to observational cosmology because its mission is to place stringent limits on six parameters that codify a cold dark-matter universe with a cosmological constant lambda that takes account of dark energy.” As such, the WAMP results are as important to high-energy physicists as to cosmologists.
Other hot topics in the physical sciences include studies of graphene, which has potential as a substitute for silicon in electronics, and the properties of the new iron-based superconductors.
Studies in clinical medicine – a few reporting surprising conclusions – dealt with prostate cancer, the drug Clopidogrel, type-2 diabetes, the H1N1 virus, the use of anti-angiogenesis treatments for cancer, and aspects of obesity. Naturally, initial reports of swine flu attracted many citations.
In the area of basic biomedical research, micro-RNAs and other small RNAs, induced pluripotent stem cells and the role of inflammasome in immune responses stand out.
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