Cited References Explorer


Which are the most important papers in the history of a field? On whose shoulders of giants does an author stand? Where to look for the intellectual roots of a research topic? These questions can be answered by using the program CitedReferencesExplorer (CRExplorer).

The CRExplorer uses data from Web of Science (Clarivate Analytics) or Scopus (Elsevier) as input. Publication sets have to be downloaded including the references cited. The program focusses on the analysis of the cited references, in particular on the referenced publication years. Over time, "citation classics" of a field become more pronounced. When the aggregated citations are plotted along the time axis, one obtains a "spectrogram" with distinct peaks. CRExplorer visualizes this spectrogram, cleans the cited references (so-called "disambiguation"), and uses a smoothing algorithm to suppress the noise.

The method Reference Publication Year Spectroscopy (RPYS) was developed by Werner Marx, who used it for the first time in the field of meteorology (see his study on page 11). For demonstration of the potential of the method, figure 1 shows the citation classics concerning the discovery of the “greenhouse effect”, a basic component of climate change.

Figure 1
Figure 1: Citation classics concerning the discovery of the “greenhouse effect” and appearing as peaks in the spectrogram provided by the CRExplorer.

We downloaded from the Web of Science 3,244 publications containing the term "greenhouse effect” in the title or in the abstract or as a keyword. These papers contain 81,126 references to publications published over 379 years. The graph produced by the CRExplorer shows three distinct peaks during the 19th century and a few others during the first half of the 20th century.

The first three pronounced peaks go back to the following publications:

The subsequently following peaks can be assigned to the works of Chamberlin (1898), Arrhenius (1908), and Callendar (1938, 1949). These are citation classics in the climate change literature. They deal with the possibility that climatic change results from changes in the concentration of atmospheric carbon dioxide—thereby supporting the calculationtheory of Arrhenius. Whereas Chamberlin (1898) and Callendar (1938, 1949) have been written for scientists, Arrhenius (1908) book was directed at a general audience.

In sum, the discovery of the earth’s greenhouse effect and the role of carbon dioxide and water vapor as greenhouse gases are no recent findings but date back to the beginning of the nineteenth century. (See here for more information.)

Running CRExplorer & System Requirements

CRExplorer requires a system with Java 8 support. There are two options to run CRExplorer in the GUI mode:

  1. Download: You can download a runnable JAR file. On most systems a double click on the JAR file will start CRExplorer. If you want to run the JAR file from command line please refer to the official Java documentation on Running JAR-Packaged Software. Here you can also set the heap space size if you are processing large files.

If you want to employ CRExplorer's script language, you can download a runnable JAR file that can be started from the command line as follows:

java -jar CitedReferencesExplorerScript.1.9.0.jar []
where [] should be replaced by the user's script filename.


CRExplorer version 1.9 was released on July 16, 2018. This version includes the following new features and improvements:

CRExplorer version 1.8.2 was released on February 1, 2018. This version includes the following new features and improvements:

CRExplorer version 1.7.7 was released on June 30, 2017. This version includes the following new features and improvements:

CRExplorer version 1.7.5 was released on May 31, 2017. This version includes the following new features and improvements:

CRExplorer version 1.6.8 was released on August 29, 2016. This version includes the following new features and improvements:

CRExplorer version 1.6.7 was released on July 5, 2016. This version includes the following new features and improvements (see New features of CRExplorer for a detailed description):

Guide and Datasets

  1. CitedReferencesExplorer (CRExplorer) Manual
    by Andreas Thor, Werner Marx, and Lutz Bornmann

  2. Introducing CitedReferencesExplorer (CRExplorer): A program for Reference Publication Year Spectroscopy with Cited References Disambiguation
    by Andreas Thor, Werner Marx, Loet Leydesdorff, and Lutz Bornmann (arXiv)

  3. New features of CitedReferencesExplorer (CRExplorer)
    by Andreas Thor, Werner Marx, Loet Leydesdorff, and Lutz Bornmann (arXiv)

  4. Identifying single influential publications in a research field: New analysis opportunities of the CRExplorer
    by Andreas Thor, Lutz Bornmann, Werner Marx, and Rüdiger Mutz (arXiv)

  5. How to identify the roots of broad research topics and fields? The introduction of RPYS sampling using the example of climate change research
    by Robin Haunschild, Werner Marx, Andreas Thor, and Lutz Bornmann (arXiv)



Software Development

Andreas Thor
University of Applied Sciences for Telecommunications Leipzig (HfTL)
Gustav-Freytag-Str. 43-45
04277 Leipzig, Germany

Questions? Bugs? Feature wishes? Please send us feedback!

Content Development

Lutz Bornmann
Division for Science and Innovation Studies
Administrative Headquarters of the Max Planck Society
Hofgartenstr. 8
80539 Munich, Germany

Robin Haunschild
Max Planck Institute for Solid State Research
Heisenbergstr. 1
70569 Stuttgart, Germany

With further support of (alphabetically ordered)

Loet Leydesdorff
Amsterdam School of Communication Research (ASCoR)
University of Amsterdam
P.O. Box 15793
1001 NG Amsterdam, The Netherlands

Werner Marx
Max Planck Institute for Solid State Research
Information Service
Heisenbergstrasse 1
70506 Stuttgart, Germany

Rüdiger Mutz
ETH Zürich
Mühlegasse 21
8001 Zurich, Switzerland

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Hochschule für Telekommunikation Leipzig (HfTL)
Gustav-Freytag-Str. 43-45,
04277 Leipzig

Contact Information

Andreas Thor
Telephone: +49 341 3062-287
Internet address:


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