仅在参考书目中使用“检索于（德语：Besucht am）” URL

Question

我希望“Besucht am:”仅在使用 URL 时才出现在参考书目中。不幸的是，“Besucht am: + 日期”出现在所有来源中，而且有数百个...

这是我的代码：

\usepackage{hyperref}
\usepackage[utf8]{inputenc}
\usepackage[ngerman]{babel}
\usepackage[backend=biber, citestyle=authoryear-icomp, bibstyle=authoryear, sorting=nyt, 
hyperref=true, uniquename=false,]{biblatex} 

这里是我的库中的两个例子 - 只有第一个应该有“Besucht am: date”：

@misc{Stiewe.2015,
 author = {M{\"u}ller, Eckhard and Stiewe, Christian},
 year = {2015},
 title = {Anwendungspotential thermoelektrischer Generatoren in station{\"a}ren Systemen Chancen f{\"u}r NRW: Studie im Auftrag des Ministeriums f{\"u}r Innovation, Wissenschaft, Forschung des Landes Nordrhein-Westfalen},
 url = {https://elib.dlr.de/100251/},
 keywords = {Anwendungspotential NRW;TEG},
 urldate = {2021-02-22}, %JJJJ-MM-TT
 editor = {{Deutsches Zentrum für Luft- und Raumfahrt e.V.}},
 institution = {{Institute of Materials Research - Thermoelectric Materials and Systems}},
 file = {673c3516-1a8e-4110-b4d2-7dccfe87d67a:C\:\\Users\\user\\AppData\\Local\\Swiss Academic Software\\Citavi 6\\ProjectCache\\mubvzqt50zkfv8qpidh93k7mxrtrdnpo3gt0y1\\Citavi Attachments\\673c3516-1a8e-4110-b4d2-7dccfe87d67a.pdf:pdf}
}
@article{Rosch.2021,
 abstract = {npj Flexible Electronics, doi:10.1038/s41528-020-00098-1},
 author = {R{\"o}sch, Andres Georg and Gall, Andr{\'e} and Aslan, Silas and Hecht, Matthias and Franke, Leonard and Mallick, Md. Mofasser and Penth, Lara and Bahro, Daniel and Friderich, Daniel and Lemmer, Uli},
 year = {2021},
 title = {Fully printed origami thermoelectric generators for energy-harvesting},
 urldate = {2021-02-22},
 pages = {1--8},
 volume = {5},
 number = {1},
 journal = {npj Flexible Electronics},
 doi = {10.1038/s41528-020-00098-1},
 file = {772ca64a-a60f-4800-be17-b8d2f74ebcae:C\:\\Users\\user\\AppData\\Local\\Swiss Academic Software\\Citavi 6\\ProjectCache\\mubvzqt50zkfv8qpidh93k7mxrtrdnpo3gt0y1\\Citavi Attachments\\772ca64a-a60f-4800-be17-b8d2f74ebcae.pdf:pdf}
}

多谢！ ：）

Answer 1

URL 访问日期对于不稳定的 URL 有意义，但对于稳定的 DOI（甚至相当稳定的 elib URL）则不那么有意义。乌尔丽克·菲舍尔urldate评论说，如果你不想要它，那么简单地从文件中删除它是有意义的.bib。如果这不可能，这里有另一种方法，使用 Biber sourcemaps 来摆脱它

\documentclass[ngerman]{article}
\usepackage[T1]{fontenc}
\usepackage{babel}
\usepackage{csquotes}

\usepackage[backend=biber, style=authoryear]{biblatex}

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
      \step[notfield=url, final]
      \step[fieldset=urldate, null]
    }
  }
}

\begin{filecontents}{\jobname.bib}
@report{Stiewe.2015,
  author      = {Müller, Eckhard and Stiewe, Christian},
  year        = {2015},
  title       = {Anwendungspotential thermoelektrischer Generatoren
                 in stationären Systemen},
  subtitle    = {Chancen für NRW},
  titleaddon  = {Studie im Auftrag des Ministeriums
                 für Innovation, Wissenschaft, Forschung
                 des Landes Nordrhein-Westfalen},
  type        = {DLR-Forschungsbericht},
  url         = {https://elib.dlr.de/100251/},
  urldate     = {2021-02-22},
  institution = {Deutsches Zentrum für Luft- und Raumfahrt e.V.,
                 Institut für Werkstoff-Forschung},
  location    = {Köln},
}
@article{Rosch.2021,
  author  = {Rösch, Andres Georg and Gall, André and Aslan, Silas
             and Hecht, Matthias and Franke, Leonard
             and Mallick, Md. Mofasser and Penth, Lara
             and Bahro, Daniel and Friderich, Daniel and Lemmer, Uli},
  year    = {2021},
  title   = {Fully printed origami thermoelectric generators for energy-harvesting},
  urldate = {2021-02-22},
  pages   = {1--8},
  volume  = {5},
  number  = {1},
  journal = {npj Flexible Electronics},
  doi     = {10.1038/s41528-020-00098-1},
}
\end{filecontents}
\addbibresource{\jobname.bib}
\addbibresource{biblatex-examples.bib}

\begin{document}
Lorem \autocite{sigfridsson,Stiewe.2015,Rosch.2021}

\printbibliography
\end{document}

注意对您的条目所做的更改，Stiewe.2015以使其更具biblatex-y。

---

对源图代码的简短解释性注释

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
      \step[notfield=url, final]
      \step[fieldset=urldate, null]
    }
  }
}

1. 第一个\step检查是否存在url字段（notfield=url），否则停止（final）。
2. \step现在，仅在没有字段时才执行第二个操作url，并将urldate（fieldset=urldate）设置为null，即删除它。

有关 sourcemap 语法和示例的更多详细信息，请参阅文档biblatex​, §4.5.3动态修改数据，第 196-208 页（在 v3.16 中）。