How to reference an bibliography item but not as a citation

Question

The citation style in my document uses superscripts for the reference number. I would like to reference a bibliography item in-line once using just the reference number. I'm sure this is a simple thing to do, I just don't know how to phrase this question for google. I'm using natbib and the references are set up in the preamble with:

\renewcommand{\bibname}{References}
\usepackage[numbers, super,sort&compress, sectionbib]{natbib}
\usepackage{chapterbib}

I want my graphic caption to say this (I have underlined in red the portion of the caption i need help with):

The latex snippet that generated this is simple:

\begin{figure}[hb!]
\centering
\includegraphics[width = 5in]{ch1_ehtylene_MO.png}
\caption{[Rest of Text] ...  Reproduced from reference 20. Copyright (2002) National Academy of Sciences}
\label{ch1_mo}
\end{figure}

What I want is to use a command to reference the bibliography with the result the reference number inline so that way it updates as I continue editing my document. something like \cite:

\begin{figure}[hb!]
\centering
\includegraphics[width = 5in]{ch1_ehtylene_MO.png}
\caption{[Rest of Text] ...  Reproduced from reference \cite{ethylene}. Copyright (2002) National Academy of Sciences}
\label{ch1_mo}
\end{figure}

The problem is that using \cite like this ends up with a superscript, which I do not want:

Is there a command to reference the .bib entry and return the reference number in-line?

Answer 1

Using \citenum{<key>} as suggested by moewe works