| Closed Access | Embargo | Metadata Only Access | Open Access | Restricted | Unknown | Total | |
|---|---|---|---|---|---|---|---|
| Total | 19 | 5 | 1806 | 7470 | 6630 | 1100 | |
| 2025 | - | - | 3 | 2 | - | - | 5 |
| 2024 | - | 3 | 12 | 305 | 62 | - | 382 |
| 2023 | - | 1 | 17 | 443 | 77 | 2 | 540 |
| 2022 | - | 1 | 41 | 465 | 115 | 1 | 623 |
| 2021 | - | - | 24 | 403 | 104 | 1 | 532 |
| 2020 | - | - | 29 | 364 | 108 | 2 | 503 |
| 2019 | 1 | - | 38 | 429 | 101 | 1 | 570 |
| 2018 | - | - | 29 | 371 | 82 | - | 482 |
| 2017 | - | - | 53 | 270 | 169 | - | 492 |
| 2016 | - | - | 50 | 308 | 216 | 4 | 578 |
| 2015 | - | - | 39 | 320 | 226 | 8 | 593 |
| 2014 | - | - | 38 | 159 | 402 | 7 | 606 |
| 2013 | - | - | 33 | 153 | 397 | 2 | 585 |
| 2012 | - | - | 55 | 93 | 314 | 1 | 463 |
| 2011 | - | - | 60 | 94 | 346 | 9 | 509 |
| 2010 | - | - | 56 | 120 | 317 | 4 | 497 |
| 2009 | - | - | 45 | 141 | 270 | 8 | 464 |
| 2008 | - | - | 58 | 156 | 276 | 11 | 501 |
| 2007 | 1 | - | 123 | 144 | 374 | 10 | 652 |
| 2006 | - | - | 75 | 162 | 278 | 12 | 527 |
| 2005 | 1 | - | 32 | 156 | 252 | 9 | 450 |
| 2004 | - | - | 34 | 211 | 222 | 7 | 474 |
| 2003 | 1 | - | 81 | 159 | 198 | 15 | 454 |
| 2002 | 1 | - | 71 | 136 | 127 | 16 | 351 |
| 2001 | 1 | - | 103 | 131 | 112 | 46 | 393 |
| 2000 | - | - | 76 | 141 | 103 | 21 | 341 |
| 1999 | 1 | - | 82 | 102 | 111 | 29 | 325 |
| 1998 | - | - | 97 | 110 | 108 | 24 | 339 |
| 1997 | - | - | 11 | 74 | 86 | 13 | 184 |
| 1996 | - | - | 19 | 59 | 99 | 10 | 187 |
| 1995 | - | - | 24 | 102 | 74 | 13 | 213 |
| 1994 | - | - | 15 | 102 | 75 | 14 | 206 |
| 1993 | - | - | 19 | 69 | 54 | 16 | 158 |
| 1992 | - | - | 22 | 84 | 67 | 28 | 201 |
| 1991 | - | - | 14 | 77 | 62 | 17 | 170 |
| 1990 | 5 | - | 9 | 74 | 54 | 11 | 153 |
| 1989 | 1 | - | 32 | 87 | 61 | 35 | 216 |
| 1988 | - | - | 19 | 94 | 59 | 39 | 211 |
| 1987 | - | - | 16 | 63 | 50 | 27 | 156 |
| 1986 | - | - | 11 | 97 | 51 | 44 | 203 |
| 1985 | 1 | - | 32 | 41 | 67 | 53 | 194 |
| 1984 | - | - | 15 | 43 | 65 | 46 | 169 |
| 1983 | - | - | 20 | 47 | 48 | 29 | 144 |
| 1982 | - | - | 17 | 42 | 14 | 56 | 129 |
| 1981 | - | - | 21 | 37 | 16 | 53 | 127 |
| 1980 | 1 | - | 6 | 26 | 41 | 41 | 115 |
| 1979 | - | - | 5 | 21 | 31 | 48 | 105 |
| 1978 | - | - | 4 | 25 | 23 | 39 | 91 |
| 1977 | - | - | 4 | 31 | 12 | 33 | 80 |
| 1976 | 1 | - | 1 | 22 | 12 | 38 | 74 |
| 1975 | 1 | - | 4 | 29 | 10 | 33 | 77 |
| 1974 | 1 | - | - | 25 | 8 | 24 | 58 |
| 1973 | - | - | 3 | 26 | 4 | 18 | 51 |
| 1972 | - | - | 4 | 9 | 2 | 20 | 35 |
| 1971 | - | - | 3 | 2 | 8 | 10 | 23 |
| 1970 | 1 | - | 1 | 6 | 4 | 8 | 20 |
| 1969 | - | - | - | 1 | 5 | 17 | 23 |
| 1968 | - | - | 1 | 2 | 1 | 10 | 14 |
| 1967 | - | - | - | 4 | - | 6 | 10 |
| 1966 | - | - | - | - | - | 1 | 1 |
| 1965 | - | - | - | 1 | - | - | 1 |