The tools below all brand themselves in various ways: as time-savers, as replacements to e-Tables of Contents (e-TOC), or as better way to search the literature. Most of these comapnies are not stable library resource vendors, so if you like a tool, be prepared for a startup environment — not everything on the Internet perserveres.
Many of these tools are also strongest in life sciences domains, with widely variant coverage of the physical sciences and poor coverage of the social sciences.
Sparrho is a recommendation engine for scientific information. It was founded in 2013 by researchers in the United Kingdom. As with most of these tools, it is strongest in medical and life sciences literature, but has decent content discovery potential for physical scientists.
PubChase focuses on literature in the medical field, and it queries the National Library of Medicine database to find relevant biomedical literature. Their services are not affiliated with NCBI.
Have you been hoping for a tool focusing on the physical sciences? That's where Arximedes comes in. Arximedes focuses on the Physical Sciences and Techonoly fields, using the arXiv and the NASA ADS bibliographic database to generate its content. It covers 4000+ journals and contains numerous visualization features.