Your "crafted" thebibliography environment does not consist of fields like author and title, but simply of unlabeled strings separated by \newblock. Therefore, it is not possible to extract specific information. Instead, you must use packages like biblatex that resort to a bibliography database managed by backend programs like biber or BibTeX. Below, you'll find a compilable example using biblatex -- the filecontents package is used to "store" the .bib database within the example.
Make sure to compile the example using pdflatex -- biber -- pdflatex. If your editor doesn't handle this automatically, use the command line.
See section 3.7.7 of the biblatex manual for details about the \citelist command and its cousins \citename and \citefield. Note that some standard BibTeX field types are replaced with other types by biblatex (e.g. journal becomes journaltitle); while the old types work in the .bib file, you must use their biblatex equivalent within \citefield.
\documentclass{beamer}
\usepackage{biblatex}
\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@book{A01,
author = {Author, A.},
year = {2001},
title = {Alpha},
location = {Somewhere},
publisher = {A publisher},
}
\end{filecontents}
\addbibresource{\jobname.bib}
\begin{document}
\begin{frame}
As was shown by \citeauthor{A01} in \citeyear{A01} (published in
\citelist{A01}{location})~\dots
\printbibliography
\end{frame}
\end{document}

\newblocks? But beamer can colour them separately. – bkarpuz Jul 01 '13 at 11:38beameruses certain colours e.g., for the first, second, ... last block (and makes implicit assumptions about the content of these blocks), but that doesn't equal being able to extract the information. – lockstep Jul 01 '13 at 11:42\usepackage[backend=bibtex]{biblatex}and try to compile using pdflatex -- bibtex -- pdflatex. I'm fairly sure WinEdt allows to do this automatically. – lockstep Jul 01 '13 at 12:09\beamertemplatebookbibitems. Does this apply? – bkarpuz Jul 01 '13 at 12:20\renewcommand*{\newunitpunct}{\addcomma\space}Ad b) I don't know -- you should ask a new question and wait for abeamerexpert to answer it. – lockstep Jul 01 '13 at 12:29JOURNAL,VOLUME,YEAR,NUMBERandPAGESinformation for my entry but why\citelist{MR2000143}{JOURNAL}does not call the value? – bkarpuz Jul 01 '13 at 16:03\citefieldfor these. – lockstep Jul 01 '13 at 16:04JOURNAL? So that I can modify it for my other purposes. Sorry to ask too much. – bkarpuz Jul 01 '13 at 16:22\citefield{<key>}{journaltitle}, becausebiblatextreats thejournalfield as an alias of itsjournaltitle. P.S.: If it works now, please accept my answer. – lockstep Jul 01 '13 at 16:29