Dear Imran,

Please follow these links for the answer.

https://www.quora.com/What-is-the-difference-between-Letters-and-Articles-in-Nature-magazine

http://blogs.nature.com/nautilus/2009/12/difference_between_nature_arti.html

Best of Luck

Imran:

Your Question is as ambiguous as the possible answer. Perhaps you mean Letter/Communication and Articles. This link in my opinion furnishes essential difference between the two for papers published in highly rated journals like NATURE and SCIENCE:

http://talk.collegeconfidential.com/graduate-school/1239968-difference-between-a-article-and-a-letter-communication.html

Best

Syed