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| Entrez | PubMed | Nucleotide | Protein | Genome | Structure | OMIM | PMC | Journals | Books |
EFetch: Retrieves records in the requested format from a list of one or more UIs or from user's environment. Click on a database below to display database specific documentation.
Base URL: http://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?
URL parameters: (NOTE: Utility parameters may be case sensitive. Use lower case characters in all parameters except for WebEnv.
Database (Click the appropriate section in the Table of Contents for database specific URL parameters.)
db=database nameWeb Environment: Value previously returned in XML results from ESearch and used with EFetch in place of primary ID result list.
WebEnv=WgHmIcDG], etc.Query_key: The value used for a history search number or previously returned in XML results from ESearch or EPost.
query_key=6Note: WebEnv is similar to the cookie that is set on a user's computers when accessing PubMed on the web. If the parameter usehistory=y is included in an ESearch URL both a WebEnv (cookie string) and query_key (history number) values will be returned in the results. Rather then using the retrieved PMIDs in an EFetch URL you may simply use the WebEnv and query_key values to retrieve the records. WebEnv will change for each ESearch query.
Tool: is a string with no internal spaces that identifies the resource which is using Entrez links (e.g., tool=flybase). This argument is used to help NCBI provide better service to third parties generating Entrez queries from programs. As with any query system, it is sometimes possible to ask the same question different ways, with different effects on performance. NCBI requests that developers sending batch requests include a constant 'tool' argument for all requests using the utilities.
tool=E-mail Address: If you choose to provide an email address, we will use it to contact you if there are problems with your queries or if we are changing software interfaces that might specifically affect your requests. If you choose not to include an email address we cannot provide specific help to you, but you can still sign up for utilities-announce to receive general announcements.
email=