If a publication is freely available (open access), it will be marked by .1 The mark will link to a version that can be downloaded for free.
The color of the symbol indicates the kind of open access. If it is orange (), the final version of the document is freely available under a license that allows redistribution and reuse. If it is green (), the final version of the document can be accessed for free somewhere, sometimes at the publisher’s website. Finally, if it is grey (), only a postprint or arXiv version is available. ↩