Which address of availability do I state at e-resources available online and what is DOI?
The citation always contains full url of the citation where the given information source is located. It is not sufficient to use only: “Available from www.idnes.cz”, it is recommended not to use any shorteners. The availability stated by means of the main url address of the web location/main page may be used only exceptionally, in particular for statistical databases, where the given website with the given data may not be display again (but such an url address must be verified by means of a new window in a new browser , but beware of cookies).
It may happen at e-resources that the URL address is not permanent, that we may not find the given idea on the website of the url address ceased to exist. At some information sources (most often at articles, e-books and other information sources from the databases) often contain the DOI identifier (warning: it may not be found at common www websites or new portals). DOI (Digital Objective Identifier) is a centralized commercial system for unique identification of works available in digital form. To identify the source by means of DOI, the portal www.doi.org is used. Because of this identifier the given information source can always be clearly identified and accessible; it may be transformed to url address easily, when we write http://dx.doi.org, e.g. http://dx.doi.org/10.7763/IJTEF.2013.V4.318