| Closed Access | Open Access | Restricted | Unknown | Total | |
|---|---|---|---|---|---|
| 2019 | - | 75 | - | 34 | 109 |
| 2018 | - | 250 | - | 83 | 333 |
| 2017 | 4 | 48 | 2 | 361 | 415 |
| 2016 | 1 | 49 | 2 | 463 | 515 |
| 2015 | 2 | 53 | 3 | 488 | 546 |
| 2014 | 9 | 39 | 2 | 542 | 592 |
| 2013 | 24 | 40 | 4 | 496 | 564 |
| 2012 | 12 | 41 | 1 | 384 | 438 |
| 2011 | 15 | 31 | 4 | 436 | 486 |
| 2010 | 15 | 22 | 1 | 450 | 488 |
| 2009 | 8 | 9 | - | 437 | 454 |
| 2008 | 2 | 19 | - | 473 | 494 |
| 2007 | 1 | 16 | - | 632 | 649 |
| 2006 | - | 4 | - | 510 | 514 |
| 2005 | - | 12 | - | 429 | 441 |
| 2004 | 2 | 6 | - | 460 | 468 |
| 2003 | - | 4 | - | 449 | 453 |
| 2002 | - | 4 | - | 345 | 349 |
| 2001 | - | 3 | - | 383 | 386 |
| 2000 | - | 1 | - | 53 | 54 |
| 1999 | - | 2 | - | 49 | 51 |
| 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 | 95 | 728 | 19 | 8261 |