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?	Country	Papers	Citations	Citations per paper
1	United States	53,300	1,092,808	20.50
2	England	11,873	236,079	19.88
3	The Netherlands	4,753	93,530	19.68
4	Switzerland	3,152	61,485	19.51
5	Denmark	2,184	42,518	19.47
6	Scotland	3,103	57,433	18.51
7	Germany	14,816	257,994	17.41
8	Belgium	2,978	51,818	17.40
9	France	11,568	200,919	17.37
10	Austria	1,528	25,804	16.89
11	Norway	933	15,499	16.61
12	Australia	4,702	77,559	16.49
13	Wales	664	10,838	16.32
14	Sweden	3,044	49,632	16.30
15	Canada	6,357	102,201	16.08
16	Ireland	1,024	16,192	15.81
17	Finland	1,496	22,937	15.33
18	Israel	1,481	21,434	14.47
19	South Africa	998	14,039	14.07
20	New Zealand	867	11,613	13.39

The data above were extracted from the Essential Science Indicators database of Thomson Reuters. This database, currently covering the period January 1999 to June 2009, surveys only journal articles (original research reports and review articles) indexed by Thomson Reuters. Articles are assigned to a category based on the journals in which they were published and the Thomson Reuters journal-to-category field-definition scheme. Both articles tabulated and citation counts to those articles are for the period indicated.

Here our ranking in microbiology is by citations per paper ¨C among nations that collected 10,000 or more citations during the period ¨C to reveal weighted impact. For articles with multiple authors from different nations, each nation receives full, not fractional, citation credit. Essential Science Indicators lists nations ranked in the top 50 per cent for a field over a given period, based on total citations. In microbiology, 88 nations are listed, meaning 176 were surveyed. Thirty-four nations collected at least 10,000 citations. For more information on Thomson Reuters Essential Science Indicators, see .