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Searching the Scientific Literature

"Publications are at once the end-product of scientific research and the raw material for future research." (A.F Spillhaus)

journal paper Initial Planning:
    Reasons for Searching

    Narrowing or Broadening Your Research Topic

    Focusing Your Search--Primary or Secondary Literature
Approaches to Searching:
    Subject Searching Citation Searching


Scientific research is a cumulative process with present research building upon a knowledge base of information that resides in the scientific literature. Following are three reasons why you may need to find, evaluate and use this literature.
Knowledge Base


Researchers usually focus on a specific attribute of the natural world. You should use a scientific mindset to first define a specific hypothesis or research question before looking for information that either substantiates or refutes the hypothesis or answers the research question. In some cases you will need to spend time working through your initial hypothesis to narrow your topic so you are not looking through volumes of information. In some cases you will need to broaden your original hypothesis, e.g. to a broader group of organisms.

As an example the general research topic of "giant squid" could be subdivided into five sub-topics of "location", "habitat", "predators", "anatomy" and "legends'. "Habitat" could then be subdivided into even more specific sub-topics. The goal is to eventually arrive at a workable hypothesis or research question.

giant squid topics

Examples of research questions that could be formulated using the above include:

    How does the giant squid navigate without light?
    How does the giant squid cope with intense pressure?
    What are the feeding habits of giant squid?

For other general concepts on narrowing or broadening your research topic see Research Roadmap.

FOCUSING YOUR SEARCH--primary or secondary scientific literature

One of the first steps in developing a search strategy is deciding where to initially focus your literature search--primary or secondary literature. For a more detailed introduction see Literature of Science.

To search for primary literature use literature databases that are listed under Articles and Databases on the Library's web page. Every scientific discipline has at least one database to its research literature. You can use a combination of subject searching and citation searching to locate desired information.

To search for books and government documents that are part of the secondary literature use the HSU Library Catalog, the catalogs of Other Libraries and the Catalog of U.S. Government Publications. In addition many of the Research Guides developed by HSU librarians list important secondary reference tools in the HSU Library and on the Internet that can be used as starting points for research. Sometimes an older bibliography will comprehensively cover earlier primary literature.


This method uses "subject" keywords to search literature databases and catalogs. To effectively conduct a subject search you should first develop a subject search strategy and then think about how you will enter your search in a literature database or catalog as shown in the following example:

subject search form

  1. Develop a subject search strategy.

    Start by constructing a search strategy using the following four steps. The Search Strategy Worksheet, an expanded explanation of these four steps, can be printed and used to construct a search strategy for your research topic.

      STEP 1 -- Summarize your research topic in one or two sentences.

      I am interested in finding research on the effect of sedimentation on the survival of salmon eggs.

      STEP 2 -- Identify the unique ideas or concepts associated with your research topic.

      A research topic typically has two or three unique concepts. In the sciences these concepts commonly fall into one of these categories: subject; taxonomic; geographic; time; habitat; life stage, population or age group; organ system; chemical substance; genetic sequence; disease; or methodology, technique or test.

      Search Topic Concepts

      STEP 3 -- Brainstorm appropriate keywords for each concept.

      Each concept usually can be described using several specific keywords. These keywords can be developed in several ways - your personal knowledge of the topic, suggestions of others, or background reading that you do in secondary sources. In making a list of keywords consider the following:

      1. "Controlled Keywords"

        Many literature databases and catalogs use "controlled" keywords that come from associated thesauri or lists of keywords and which are assigned by indexers to every record in the database. These "controlled" keywords bring together similar ideas under one standardized word or phrase that may be described in the discipline literature by several different keywords. See this reference as an example of the "controlled" keywords used in an literature database. In a database record they may be called "descriptors", "subject headings", etc.

      2. Hierarchical Relationships

        In developing keyword lists consider possible hierarchical relationships within a particular concept. For example, with a taxonomic concept are you only interested in locating research on a particular species or is a broader taxonomic classification also of interest?

        marine biology

        marine flora

        marine algae

        red algae (Rhodophyta)

        coralline algae (Coralinales)


        Sporolithon ptychoides
      3. Scientific Nomenclature

        For taxonomic concepts use both common and scientific names of organisms. Using both will normally increase the number of citations retrieved.

        salmon or oncorhynchus
      4. Word Truncation

        Examine each keyword to see if it can be beneficially truncated to retrieve variant forms of the word. This is especially true for single and plural variants of a word. You can use wildcard symbols (e.g., *, #, ?, +) available in a database to truncate words back to a base root. To find the correct wild card symbols to use in a database check its help section. Examples:

        sediment* retrieves sediment, sediments, sedimentation
        silt* retrieves silt, silts, silting, silted, siltation

      STEP 4 -- Establish the relationship between each keyword and concept.

      Use Boolean operators -- AND, OR, and NOT -- and nesting to connect together every keyword and concept in your search statement. AND connects each concept and OR connects the synonymous keywords under each concept. Keywords connected by ORs need to be entered in the same search box or enclosed within parentheses ( ) when searching a database. See the sample search above as well as the following example:

      (sediment* or silt*) and (hatch* or survival) and (salmon* or oncorhynchus) and (egg* or embryo* or redd*)

  1. Strategize how to enter your search in literature databases and catalogs.

    1. Sometimes it is useful to conduct a preliminary search before beginning your main search. This search serves two purposes: 1) it is a means to get a basic sense of the literature on your topic; and 2) it serves as a source of keywords for each of your concepts and it will help you assess whether searching on specific keywords is likely to yield relevant results.
    2. Concepts within a topic are often a mixture of specific and broad ideas. A useful approach is to identify the most specific concept and search that one first. If this initial search retrieves only a few references, just browse through them and identify the ones relevant to your topic. If the search retrieves many references, add another concept using the "and" connector to decrease your results.

    3. Use "controlled" keywords as described above. If you do not know what "controlled" keywords to use, conduct an initial search using the keyword(s) you have. In reviewing the search results look for "controlled" keywords, often called descriptors or subject headings, which commonly appear as part of each citation (see example). Re-enter your search adding these "controlled" keywords to your existing keywords.

    4. Use a "building block" approach to searching if the database you are searching allows for it. Enter each of your concepts individually by ORing together the list of synonymous keywords you have created, e.g., prevent* or avoid* or deterr*. After each of your concepts has been entered use the database "Search History" feature, if available, to AND together each of the concepts. Employing this approach allows you to:
      • add new keywords you have identified to an existing concept, e.g., concept 1 or avert* (new keyword)
      • try different concept combinations using the AND connector, e.g.,

        concept 1 and concept 2 and concept 3
        concept 1 and concept 3
        concept 3 and concept 2

    5. Searching is a dynamic process. As you proceed in your literature search, and as your personal knowledge increases, your list of keywords is likely to grow and/or be refined.


As part of the research process citation is made within current publications to earlier research. Citations may serve the following purposes:

Citations are commonly included within the text of the paper and listed in a concluding "Bibliography" or "Literature Cited" section. The average research paper contains eleven citations.

Literature Cited

Starting with at least one initial research paper a bibliography of both older and newer research related to your topic can be created. The initial research paper(s) may come from several possible sources:

  1. To find older references.

    To work BACKWARD in time use the "Bibliography" or "Literature Cited" section of publications you already in hand. Just look up appropriate references cited in these publications and then continue to follow up additional references that you find in older papers. Depending upon the extent of your information needs this process can be repeated until the point is reached when you continue finding the same older references.

    Older References
  2. To find newer references.

    A number of databases allow you to work FORWARD in time from an older reference. The results of your search in these databases will be a bibliography of more recent papers that have cited your original older research paper. See Advanced Research Skills: Citation Searching for short video introduction.

    Google Scholar is the most comprehensive citation database to which the HSU Library has access.

    Google Scholar

    Other scientific literature databases available at HSU also provide citations to more recent articles. You may also be able to set up a "search alert" for new articles that have cited an article found in a database. (Note: Two comprehensive citation databases--Web of Science and Scopus--are not available at HSU.)

    Citing Article Sources
    • ACM Digital Library (HSU users only)
    • Annual Reviews
    • BioOne (HSU users only)
    • BioOne Abstracts and Indexes (HSU users only) includes "Cited by" links for both indexed articles and to each article's cited references. The citing references are taken from other CSA environmental indexes.
    • CiteSeer is a citation based index to computer and information science literature.
    • CINAHL (HSU users only)
    • Highwire Press
    • JSTOR (HSU users only)
    • MathSciNet (HSU users only) includes a "Citation Database".
    • Oxford Journals (HSU users only)
    • PsycINFO (HSU users only) includes a "Cited By" link for more recent citing references. The reference list associated with each article also includes "Cited By" links.
    • PubMed links to full text articles in the PubMed Central database that cite an article.
    • ScienceDirect (HSU users only) lists recent papers added to the ScienceDirect and Scopus databases that have cited a ScienceDirect article.
    • SciFinder (HSU users only) Includes a "Get Citing" link.