An Emacs command that takes the DOI in the clipboard and inserts the corresponding BibTeX entry at point.

insert_bibtex_from_doi.el

(require 'url-http)

(defun insert-bibtex-from-doi ()
  (interactive)
  (let* ((doi (string-trim (gui-get-primary-selection)))
         (url (if (string-prefix-p "https://doi.org/" doi)
                  doi
                (concat "https://doi.org/" doi)))
         (url-request-method "GET")
         (url-mime-accept-string "application/x-bibtex"))
    (insert
     (with-current-buffer (url-retrieve-synchronously url t)
        (goto-char (point-min))
        (while (not (looking-at "\n"))
          (forward-line 1))
        (let ((string (buffer-substring-no-properties (point) (point-max))))
          (kill-buffer)
          (decode-coding-string (string-trim string) 'utf-8))))
    (bibtex-clean-entry t)))

See also this solution: https://www.anghyflawn.net/blog/2014/emacs-give-a-doi-get-a-bibtex-entry/

Take a look at https://github.com/mpedramfar/zotra