What if there is no DOI?

Related questions

1. Is PMID same as Doi?
2. Does APA Style require DOI?
3. What does PMID mean?
4. How do you find the PMID of an article?
5. What is the difference between PMID and Pmcid?
6. What is the PubMed unique identifier PMID?
7. Where is the DOI in PubMed?
8. What is PMID number?
9. How do I search for PMID?
10. How do I search PMID PubMed?

Tags

1. #entry
2. #given
3. #means
4. #whether
5. #electronic
6. #number
7. #often
8. #online
9. #journal
10. #reference
11. #article
12. #document
13. #uncertain
14. #direct
15. #homepage
16. #searching
17. #assigned
18. #there