MassBank is a mass spectral database of experimentally acquired high resolution MS spectra of metabolites. It offers various query methods for standard spectra. The database has very detailed MS data and excellent spectral/structure searching utilities.

MassBank Documentation

Material Archiv is a network of various sample collections taken from architecture, art and design. This joint online database provided by several Swiss institutions contains basic knowledge, examples and applications related to materials such as wood, paper, metal, plastic, stone, glass, ceramics and colorants (German only).

MatNavi is an integrated material database system comprising ten databases, four application systems and the NIMS Structural Datasheet Online. MatNavi Contains data on the material properties of polymers, ceramics, superconductors, composites and diffusion. The use of MatNavi is free. All you need to do is register.

MEDLINE is the US National Library of Medicine (NLM) premier life sciences database.

Explore biomedicine and life sciences, bioengineering, public health, clinical care, and plant and animal science. Search precisely with MeSH terms and CAS registry numbers; link to NCBI databases and PubMed Related Articles. Backfiles to 1950.

Note that MEDLINE can be searched from within Web of Science.

At its most basic level, Mendeley is a free reference management tool, but it can also help with other aspects of research. Another useful feature is the crowd-sourced database of more than 30 Mio papers. Not only can you search across disciplines, but you can also limit your results to only open access content. You can also find popular groups and tags related to a paper, which could reveal a whole collection of research already created around the topic you’re searching.