Table 3 QHCs of search engines and bibliographic databases

From: Google Scholar to overshadow them all? Comparing the sizes of 12 academic search engines and bibliographic databases

Name of database Single terms Single symbols Character combination Number combination Word combination Time span/other
a 1 the ANSI a–z 0–9 Top100 Top50 Top25
AMiner No report of QHCs exceeding 1000 hits.
Bielefeld Academic Search Engine (BASE) 62,939,918 47,132,682 65,409,081 117,762,309 (*) 104,146,514 82,855,823 31,551,663 56,820,714 68,557,113 103,016,285 (0000–2018)
CiteSeerX 8,178,032 7,933,667 5,687,272 8,401,126 (*) 8,247,528 8,060,521 6,775,009 6,617,395 6,424,390 N/A (shows same result for varying time spans)
EbscoHost (selection of 25 databases—see “Appendix 1”) 20,056,140 33,851,675 823 380,143 (“) 41,092,238 37,390,677 56,597,398 48,888,668 35,458,081 102,908,910 (1550–2018)
Google Scholar 81,500,000 247,000,000 49,300,000 389,000,000 (*) 192,000,000      389,000,000 (1700–2099) (blank “common_term”)
Microsoft Academic No report of QHCs exceeding 5000 hits
ProQuest (selection of 19 databases—see “Appendix 1”) 199,100,118 150,864,723 189,797,217 279,987,039 (;) 250,422,353 247,542,112   270,846,888 270,178,534 279,987,039 (750–2030)
Q-Sensei Scholar 31,697,482 6,243,396 36,370,496 8,168,464 (&) 228 (a-y) 50,751    2,137 (Top8) 47,195,502 (1969–2017; all available years selected) 55,162,101 (all “type-facets” selected)
Scopus 60,433,436 40,156,373 63,411,230   70,995,663 66,812,009 71,091,362 70,890,200 70,683,693 72,212,354 (Top100 OR 0–9 OR a–z)
Semantic Scholar 5,350,000 5,410,000 5,320,000   2,110,000 3,190,000 204,000 370,000 1,100,000  
Web of Science (Core Collection—see “Appendix 1”) 33,832,256 10,204,360 41,791,314 67,713,141 (“:”) 39,567,990 19,942,632 63,718,875 63,206,556 62,080,068 67,713,141 (1850–2018)
Web of Science (selection of 10 databases incl. Core Collection—see “Appendix 1”) 65,500,925 22,971,331 78,714,615 105,519,854 (“:”) 75,709,357 42,252,988 101,067,361 100,510,004 99,554,354 105,519,854 (1800–2018)
WorldWideScience 306,335,673 323,202,597 234,191,957 272,392,231 (:) 72,180,354 306,097,593 29,138,581 41,847,969 41,392,251  
  1. Bold numbers indicate maximum QHCs
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