Chinese Library Classification System:
Dewey Decimal System: https://www.oclc.org/dewey/features/summaries.en.html
The above website tells the categories that Dewey has, but you can't put in a subject and tell what the Dewey number is for that subject. To do this, you have to look up a book on a given subject in First Search, and the details about that book will show the Dewey categor or number assigned to that book. Or you can look on the copyright page of the physical book, if you have access to it, or an onliine copy. WorldCat online, does not provide the Dewey number or the LOC Classsification.
DMOZ: https://www.dmoz.org/ (Alexa, Google, Yahoo, and others use DMOZ categories and subject trees;)
https://www.dmoz.org/Science/Anomalies_and_Alternative_Science/
https://www.dmoz.org/Society/Religion_and_Spirituality/Divination/Dowsing/
https://www.dmoz.org/Society/Paranormal/
Google Directory: The Google Directory no longer exists, and was shut down in 2011. Google's Directory was largely, if not totally, based on DMOZ's subject system. The URL used to be available via Google's list of services, but is no longer listed. You could get to a version by going to the Wayback Machine page:
Library of Congress (LOC): The LC Subject Authories website that used to be at http://authories.loc.gov, no longer works. The LOC Classification Outline is available at:
http://www.loc.gov/catdir/cpso/lcco/
Wikipedia Categories and Subject Trees:
You can determine what Wikipedia categories have been applied to a given subject by going to the bottom of the Wikipedia page of the subject, where a list of categories is shown;
https://en.wikipedia.org/wiki/Portal:Contents/Categories
WorldCat/OCLC: https://www.worldcat.org/
You can determine what official subject category a given book or periodical has been given, by looking up the book in WorldCat, which will show the subject categories that have been assigned to that book or other item;
Yahoo Subject Directory: The Yahoo Directory no longer exists; The URL used to be: http://dir.yahoo.com, which now gives just a blank page. You can get to a 2013 version by going to the Wayback Machine page:
http://web.archive.org/web/20131230034434/http://dir.yahoo.com/
Yellow Fellow: Website whereby you could enter a subject and it would tell you narrower terms, broader terms, related, and used for terms, just as the large hardcopy LCSH red volumes tell you. It used to be at: http://lcauth.dra.com/LCAUTH, but this website no longer exists. You can see a snapshot of it via the Wayback Machine at:
http://web.archive.org/web/20130725162531/http://lcauth.dra.com/lcauth