ChemRxiv.org
The Preprint Server for Chemistry, operated by the American Chemical Society

ChemistryViews
Chemistry Europe, an organization of 16 European chemical societies

Chemie.DE
LUMITOS

organische-chemie.ch
B. Bart, R. Müller

ATSDR
AGENCY FOR TOXIC SUBSTANCES AND DISEASE REGISTRY

ChemView
U.S. Environmental Protection Agency

GESTIS Stoffdatenbank
Gefahrstoffinformationssystem der gewerblichen Berufsgenossenschaften

Lebensmittelzusatzstoffe (E-Nummern)
Die Verbraucher Initiative, Bonn

NIOSH DATABASES
u.a. "International Chemical Safety Cards"

The Cambridge Structural Database (CSD)
The Cambridge Crystallographic Data Centre (CCDC)

CAS Common Chemistry
Open community resource for accessing chemical information. API access available.

Crystallography Open Database
Including data and software from CrystalEye

eMolecules
Search and order from over 7.3 million Building Blocks.

IUPAC Compendium of Chemical Terminology
"Gold Book" This online version corresponds to the second edition, compiled by Alan D. McNaught and Andrew Wilkinson.

IUPAC Nomenclature of Organic Chemistry
Published with permission of the IUPAC by ACD

NIST Physical Reference Data
National Institute of Standards and Technology, USA (Physikalische Konstanten und Daten)

PubChem
The world's largest collection of freely accessible chemical information, NCBI

Sigma-Aldrich
Zugang zu den Katalogen verschiedener Chemikalien-Hersteller

WebElements
Anklickbares Periodensystem, Mark Winter, University of Sheffield, England