https://www.uspto.gov/web/patents/classification/uspc244/sched244.htm
Search Patent Classification Systems
patent classificationsearchsystems
https://www.wipo.int/publications/en/details.jsp?id=4490&plang=EN
Guide to the International Patent Classification (2020)
This Guide provides information on the objectives, history and reform of the International Patent Classification (IPC) as well as assistance in the use of the...
guide tothe internationalpatent classification
https://www.prv.se/en/online-services-and-forms/patent-online-services/the-german-patent-classification-dpk/the-german-patent-classification-dpk-in-german/
The German Patent Classification (DPK) in German - PRV
Links to DPK classification schemes in German (pdf): 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38...
german patentclassificationdpkprv