- 1946 to 19499,085
- 1950 to 195410,162
- 1955 to 19597,523
- 1960 to 196413,409
- 1965 to 196915,439
- 1970 to 19749,553
- 1975 to 19799,262
- 1980 to 19846,593
- 1985 to 19898,438
- 1990 to 19943,688
- 1995 to 19995,112
- 2000 to 20021,953
The preservation of the Duke University Libraries Digital Collections and the Duke Digital Repository programs are supported in part by the Lowell and Eileen Aptman Digital Preservation Fund