I have a huge .bib file generated automatically from Papers for Mac and all the capitalization in the .bib is already the way I want it, but it doesn't have {} brackets on word like RNA.
Is there a way to force BibTeX to keep the capitalization rather than change some words to lowercase?
I agree with Killian that the right thing is to put {}s to conserve capitalisation, but I don't recommend doing this always, since the behaviour is wrong in some contexts, and not automatisable, but instead the right thing with Bibtex is to do the following:
- Put book and article titles into title case (i.e., capitalising all significant words [1], but not protecting them yet);
- Protect the capitals of all proper names, e.g., From {B}rouwer to {H}ilbert;
- Protect the capitals of all technical acronyms, e.g., The definition of {S}tandard {ML}; and
- Protect the initial word of a subtitle, e.g. the  {W}ittgenstein's Poker: {T}he story of a ten-minute argument.
Don't protect lowercase letters: this prevents Bibtex from converting the string to all-caps, which is required by some obscure bibliographical styles.
If you have been using a spell-checker, then the contents of its database will, with luck, contain nearly all of the material you need to know to capitalise properly: spell-checker's store information on which words are all-caps, and which are capitalised as proper names. If you can programmatically match words against this, then you can generate your Bibtex database automatically, with more than a little work, but it's maybe a two-hour project.
Tiresomely, Bibtex can't be used to get all bibliographies right, since different citation styles actually have different lists of non-significant words. However, in practice hardly anyone ever cares about the differences, so one can come up with a standard list of non-capitalised words.
[1] - Significant words:"a", all two-letter actual words, "the", "and", "some", all one-word prepositions, and all one-word pronouns would be an acceptable list of non-significant words , I think, to nearly all publishers.
If you prefer to edit the bibtex style (.bst) rather than the bibliography (.bib), you can  search for occurences of change.case$ in it. This is the function that capitalizes or title-izes fields that are not people names.
Typically, for the title field, you should find something like title "t" change.case$. Since you want the title unmodified, replace that by just title.
In that case you should just add {} around each entire title, which has the same effect and should be easy to do automatically.
I was getting the same issue with a title such as:
title = {blah blah AB blah AB blah}
turning out as:
"blah blah ab blah ab blah"
Using Charles Stewart's suggestion, I changed my title to:
title = {blah blah {A}{B} blah {A}{B} blah}
Now my title turns out right:
blah blah AB blah AB blah
Hope this helps.
One alternative to using {curly brackets} is this:-
- Check your root folder for .bbl file, where .bbl is your BiBteX database, after you run pdflatex for the first time and then run bibtex on your BiBteX database file.bbl. 
- Open this *.bbl file in an editor of your choice. 
- The file would look like this: - \begin{thebibliography}{10} \expandafter\ifx\csname url\endcsname \relax \def\url#1{\texttt{#1}} \fi \expandafter\ifx\csname urlprefix\endcsname \relax\def\urlprefix{URL } \fi \bibitem{label}.....
- Edit this *.bbl file to meet your requirements and now run the pdflatex command on your .tex file. This should give you the desired result. 
- By this method you can edit the bibliography in any manner. You can even add names with accented characters. 
来源:https://stackoverflow.com/questions/2800527/preserving-all-capitalization-in-bibtex