Images and OCR-text files
We have digitized complete articles or books, trying to present the article or book ‘as it is’. The preliminary pages and in some cases the cover are included as well.

The texts are presented as images offering faithful reproductions of the original sources. Wherever possible these source images are accompanied by automatically generated text files (via OCR = optical character recognition) to enable searching and copying. You can easily switch between 'image' and 'OCR-text' by clicking on the text icon .

Please note that the OCR-text files have not been corrected and will contain errors. As the OCR-text files do not always accurately reflect the original sources and may show problems of presentation, especially for formulas, tables, and mathematical symbols, please refer to the images (of the publication) as the authoritative versions.