Column chart. Data table with 10 rows and 4 columns follows.
| A.D. 2017 | A.D. 2018 | A.D. 2019 | |
|---|---|---|---|
| ACM | 3,978 | 3,540 | 3,511 |
| IEL | 157,443 | 175,829 | 161,084 |
| PQDT | 38,561 | 21,650 | 13,135 |
| SpringerLink | 40,988 | 45,133 | 33,231 |
| ISI Web of Science | 25,544 | 2,087 | 18,862 |
| ACS | 11,261 | 15,877 | 24,366 |
| Academic Search Complete | 353,268 | 67,929 | 33,577 |
| Emerald | 9,382 | 7,015 | 3,063 |
| ScienceDirect | 373,306 | 370,237 | 254,040 |