| Closed Access | Embargo | Metadata Only Access | Open Access | Restricted | Unknown | Total | |
|---|---|---|---|---|---|---|---|
| Total | 20 | 6 | 1814 | 7402 | 6600 | 1108 | |
| 2025 | - | - | - | 1 | - | - | 1 |
| 2024 | - | 3 | 21 | 249 | 52 | - | 325 |
| 2023 | - | 1 | 17 | 440 | 76 | 2 | 536 |
| 2022 | - | 1 | 41 | 462 | 114 | 2 | 620 |
| 2021 | - | - | 24 | 402 | 102 | 1 | 529 |
| 2020 | - | - | 27 | 362 | 105 | 4 | 498 |
| 2019 | 1 | 1 | 37 | 428 | 101 | 2 | 570 |
| 2018 | - | - | 29 | 371 | 82 | - | 482 |
| 2017 | - | - | 54 | 270 | 168 | - | 492 |
| 2016 | - | - | 50 | 308 | 215 | 5 | 578 |
| 2015 | - | - | 39 | 320 | 226 | 8 | 593 |
| 2014 | - | - | 38 | 159 | 402 | 7 | 606 |
| 2013 | - | - | 34 | 154 | 395 | 2 | 585 |
| 2012 | 1 | - | 55 | 93 | 313 | 1 | 463 |
| 2011 | - | - | 60 | 95 | 345 | 9 | 509 |
| 2010 | - | - | 56 | 120 | 317 | 3 | 496 |
| 2009 | - | - | 44 | 141 | 270 | 9 | 464 |
| 2008 | - | - | 57 | 158 | 273 | 12 | 500 |
| 2007 | 1 | - | 124 | 144 | 373 | 10 | 652 |
| 2006 | - | - | 75 | 162 | 277 | 13 | 527 |
| 2005 | 2 | - | 32 | 156 | 251 | 9 | 450 |
| 2004 | - | - | 34 | 211 | 221 | 7 | 473 |
| 2003 | 1 | - | 83 | 159 | 198 | 12 | 453 |
| 2002 | 1 | - | 72 | 136 | 126 | 16 | 351 |
| 2001 | - | - | 103 | 132 | 113 | 45 | 393 |
| 2000 | - | - | 76 | 140 | 103 | 22 | 341 |
| 1999 | 1 | - | 82 | 101 | 111 | 30 | 325 |
| 1998 | - | - | 98 | 111 | 107 | 23 | 339 |
| 1997 | - | - | 11 | 74 | 86 | 13 | 184 |
| 1996 | - | - | 19 | 58 | 100 | 10 | 187 |
| 1995 | - | - | 24 | 101 | 74 | 14 | 213 |
| 1994 | - | - | 15 | 102 | 75 | 14 | 206 |
| 1993 | - | - | 20 | 69 | 54 | 15 | 158 |
| 1992 | - | - | 22 | 83 | 66 | 30 | 201 |
| 1991 | - | - | 14 | 77 | 62 | 17 | 170 |
| 1990 | 5 | - | 9 | 74 | 55 | 10 | 153 |
| 1989 | 1 | - | 32 | 87 | 61 | 35 | 216 |
| 1988 | - | - | 20 | 94 | 59 | 38 | 211 |
| 1987 | - | - | 16 | 62 | 50 | 28 | 156 |
| 1986 | - | - | 11 | 96 | 50 | 46 | 203 |
| 1985 | 1 | - | 31 | 41 | 67 | 54 | 194 |
| 1984 | - | - | 14 | 43 | 66 | 46 | 169 |
| 1983 | - | - | 20 | 47 | 48 | 29 | 144 |
| 1982 | - | - | 17 | 41 | 14 | 57 | 129 |
| 1981 | - | - | 21 | 37 | 17 | 52 | 127 |
| 1980 | 1 | - | 6 | 26 | 40 | 42 | 115 |
| 1979 | - | - | 5 | 21 | 31 | 48 | 105 |
| 1978 | - | - | 4 | 25 | 23 | 39 | 91 |
| 1977 | - | - | 4 | 31 | 12 | 33 | 80 |
| 1976 | 1 | - | 1 | 23 | 12 | 37 | 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 |