| Closed Access | Open Access | Restricted | Unknown | Total | |
|---|---|---|---|---|---|
| 2019 | - | 114 | - | 46 | 160 |
| 2018 | - | 257 | - | 81 | 338 |
| 2017 | 7 | 61 | 2 | 349 | 419 |
| 2016 | 1 | 55 | 2 | 461 | 519 |
| 2015 | 3 | 54 | 3 | 489 | 549 |
| 2014 | 9 | 39 | 2 | 544 | 594 |
| 2013 | 18 | 49 | 4 | 499 | 570 |
| 2012 | 10 | 44 | 1 | 386 | 441 |
| 2011 | 9 | 39 | 3 | 439 | 490 |
| 2010 | 13 | 27 | 1 | 447 | 488 |
| 2009 | 6 | 12 | - | 436 | 454 |
| 2008 | 3 | 22 | - | 469 | 494 |
| 2007 | 1 | 20 | - | 628 | 649 |
| 2006 | - | 4 | - | 510 | 514 |
| 2005 | - | 12 | - | 429 | 441 |
| 2004 | 2 | 7 | - | 459 | 468 |
| 2003 | - | 6 | - | 447 | 453 |
| 2002 | - | 4 | - | 345 | 349 |
| 2001 | - | 4 | - | 382 | 386 |
| 2000 | - | 5 | - | 325 | 330 |
| 1999 | - | 3 | - | 253 | 256 |
| 1998 | - | - | - | 52 | 52 |
| 1997 | - | - | - | 28 | 28 |
| 1996 | - | - | - | 23 | 23 |
| 1995 | - | - | - | 33 | 33 |
| 1994 | - | - | - | 41 | 41 |
| 1993 | - | - | - | 24 | 24 |
| 1992 | - | - | - | 22 | 22 |
| 1991 | - | - | - | 13 | 13 |
| 1990 | - | - | - | 10 | 10 |
| 1989 | - | - | - | 10 | 10 |
| 1988 | - | - | - | 7 | 7 |
| 1987 | - | - | - | 5 | 5 |
| 1986 | - | - | - | 5 | 5 |
| 1985 | - | - | - | 8 | 8 |
| 1984 | - | - | - | 3 | 3 |
| 1983 | - | - | - | 2 | 2 |
| 1982 | - | - | - | 1 | 1 |
| 1981 | - | - | - | 1 | 1 |
| 1980 | - | - | - | 3 | 3 |
| 1979 | - | - | - | 1 | 1 |
| 1968 | - | - | - | 12 | 12 |
| Total | 82 | 838 | 18 | 8728 |