The search is based on Lucene, so you can use the Lucene Query Syntax, e.g.

• negative Empfindungswerte searches for negative or Empfindungswerte
• negative AND Empfindungswerte searches for negative and Empfindungswerte
• "negative Empfindungswerte" searches for negative Empfindungswerte
• Empfindungswerte~ searches for Words similar to Empfindungswerte
• "negative Empfindungswerte"~10 searches for Words similar to negative and Empfindungswerte separate by up to 10 words

Technical Credit: Automatic OCR is done with tesseract and OCRopus(tm)