Changes in the absolute numbers and proportions of open access articles from 2000 to 2021 based on the Web of Science Core Collection: a bibliometric study

Purpose: The ultimate goal of current open access (OA) initiatives is for library services to use OA resources. This study aimed to assess the infrastructure for OA scholarly information services by tabulating the number and proportion of OA articles in a literature database. Method: We measured the absolute numbers and proportions of OA articles at different time points across various disciplines based on the Web of Science (WoS) database. Results: The number (proportion) of available OA articles between 2000 and 2021 in the WoS database was 12 million (32.4%). The number (proportion) of indexed OA articles in 1 year was 0.15 million (14.6%) in 2000 and 1.5 million (48.0%) in 2021. The proportion of OA by subject categories in the cumulative data was the highest in the multidisciplinary category (2000–2021, 79%; 2021, 89%), high in natural sciences (2000–2021, 21%–46%; 2021, 41%–62%) and health and medicine (2000–2021, 37%–40%; 2021, 52%–60%), and low in social sciences and others (2000–2021, 23%–32%; 2021, 36%–44%), engineering (2000–2021, 17%–33%; 2021, 31%–39%) and humanities and arts (2000–2021, 11%–22%; 2021, 28%–38%). Conclusion: Our study confirmed that increasingly many OA research papers have been published in the last 20 years, and the recent data show considerable promise for better services in the future. The proportions of OA articles differed among scholarly disciplines, and designing library services necessitates several considerations with regard to the customers’ demands, available OA resources, and strategic approaches to encourage the use of scholarly OA articles.