Adding text between Bibliography header and the first bibitem

Question

I want to add text in to the Bibliography right after the header and before the first bibitem, so that it is structured as in the following:

References and further reading

This and that can be found in [1]. The other stuff is particularly well explained in [2] and [3]. ...

[1] ... [2] ...

(As you can see, I also want to have the header saying "References and further reading", instead of "Bibliography, but this I already managed to do that by renewing the \bibname command.)

A similar question was discussed and answered here: Headings inside the Bibliography list. The simplest solution was to add the text with the \item command, such as: \item[]\hspace{-\labelwidth}\hspace{-\labelsep}Here is the text. While this does work for headers, it does not for one or several paragraphs of text, since the layout is messed up.

Can anyone tell me how I can do this? Would be glad if there was a simple solution, but am happy for any help, thanks! :)

Some more information on my document: I use the AMSbook class. The document consists of three parts, where each one has it's own bibliography, created with the thebibliography environment. I do use the \hyperref package, and want all Bibliographies to be properly displayed (clickable) in the table of content, which works fine as it is now.

EDIT - Comments on the answers of Gonzalo Medina and Guido:

Both these approaches work, thanks! I have chosen to use Guido's approach, since it is simpler as long as one has no problem with using the natbib package. Anyway, both methods produce equally good results and fit directly to my needs, thanks! :)

Answer 1

The natbib package has a \bibpreamble hook. You can populate the text with \renewcommand{\bibpreamble}{<text>}.

\documentclass{amsbook}
\usepackage[numbers]{natbib}
\renewcommand{\bibfont}{\small}

\begin{document}

\renewcommand{\bibpreamble}{First. This and that can be found in~\cite{testa}. 
  The other stuff is particularly well explained in~\cite{testb} 
  and~\cite{testc}.}
\begin{thebibliography}{9}
\bibitem{testa} Test A.
\bibitem{testb} Test B.
\bibitem{testc} Test C.
\end{thebibliography}

\renewcommand{\bibpreamble}{Second. This and that can be found in~\cite{testd}. 
  The other stuff is particularly well explained in~\cite{teste} 
  and~\cite{testf}.}
\begin{thebibliography}{9}
\bibitem{testd} Test A.
\bibitem{teste} Test B.
\bibitem{testf} Test C.
\end{thebibliography}

\renewcommand{\bibpreamble}{Third. This and that can be found in~\cite{testg}. 
  The other stuff is particularly well explained in~\cite{testg} 
  and~\cite{testi}.}
\begin{thebibliography}{9}
\bibitem{testg} Test A.
\bibitem{testh} Test B.
\bibitem{testi} Test C.
\end{thebibliography}
\end{document}

EDIT For the font \renewcommand{\bibfont}{\small} changes the font (size) for the bibliography (but not the preamble).

Answer 2

One possible solution; in the code below I defined a \bibNote command that allows the placement of text after the heading and before the first bibitem; the font for this note can be changed by redefining the \Notefont command (default value \normalsize). A redefinition of \bibname allows to change the heading.

\documentclass{amsbook}

\renewcommand\bibname{References and further reading}

\makeatletter
\newcommand\Notefont{\normalsize}
\long\def\bibNote#1{\gdef\@bibNote{\item[]{\Notefont#1}}}
\renewenvironment{thebibliography}[1]{%
  \@xp\chapter\@xp*\@xp{\bibname}%
  \normalfont\footnotesize\labelsep .5em\relax
  \renewcommand\theenumiv{\arabic{enumiv}}\let\p@enumiv\@empty
  \list{\@biblabel{\theenumiv}}{\@bibNote\settowidth\labelwidth{\@biblabel{#1}}%
    \leftmargin\labelwidth \advance\leftmargin\labelsep
    \usecounter{enumiv}}%
  \sloppy \clubpenalty\@M \widowpenalty\clubpenalty
  \sfcode`\.=\@m
}{%
  \def\@noitemerr{\@latex@warning{Empty `thebibliography' environment}}%
  \endlist
}
\makeatother

\bibNote{This and that can be found in~\cite{testa}. The other stuff is particularly well explained in~\cite{testb} and~\cite{testc}.}

\begin{document}

\begin{thebibliography}{9}
\bibitem{testa} Test A.
\bibitem{testb} Test B.
\bibitem{testc} Test C.
\end{thebibliography}

\end{document}

If babel is being used, the redefinition of \bibname has to be done using \addto\captions<language>; for example, if the document contains

\usepackage[english]{babel}

one has to say

\addto\captionsenglish{%
  \renewcommand\bibname{References and further reading}}

Answer 3

I think this should work:

\renewcommand\bibname{References\\
\normalsize{} Citation data collected from Scopus 
(Elsevier) Sep. 6 2017.}

An example:

\documentclass\[a4paper,12pt\]{report}

\renewcommand\bibname{List of books\\ \vspace{10mm} \normalsize{} Note: Strindberg has also written other books.}

\bibliographystyle{plain}

\begin{document}

One book written by Strindberg is Hems\"{o}borna \cite{book1}.

\begin{thebibliography}{9}

\bibitem{book1}
    August Strindberg, \textit{Hems\"{o}borna}, 1887.
\end{thebibliography}

\end{document}