A scientific abstract summarizes your research paper or article in a concise, clearly written way that informs readers about the article's content. Researchers use abstracts to determine whether a paper is relevant to their work and/or decide which papers to acquire and read. For academic conferences, participants only receive copies of the abstracts in proceedings. When readers search through electronic databases for articles, the abstract is usually the sole part of the paper that they see without cost. Typically 200-250 words, a scientific abstract consists of five key parts: title and author information, background, methods, results, and conclusions. 
I often write or revise abstracts last. The ideal time for me is after working through the entire article or proposal. Not immediately after, when I'm tired and may be tempted to dash off something quick; but just long enough for it all to percolate and brew up a clear vision of what I've accomplished. If such vision appears, I just do my best-or possibly decide the article really lacks coherence and needs yet another thorough overhaul! If the vision does appear, I try to capture a good snapshot for the harried potential reader, hoping at least one of us will benefit.
Writing for an Audience Who is your audience?