API Comparison Matrix

Reference guide comparing all supported academic APIs.

Quick Comparison

API	Coverage	API Key	Rate Limit	Abstracts	Citations	DOI	Best For
Semantic Scholar	200M+ papers	Optional	1 req/s	95%	Yes	85%	AI/CS research
OpenAlex	250M+ works	No	10 req/s	60%	Yes	90%	Broad coverage
IEEE Xplore	5M+ docs	Required	200/day	100%	Limited	95%	Engineering
Elsevier	18M+ articles	Required	Varies	80%	No	100%	Life sciences
Springer	13M+ docs	Required	5000/day	90%	No	98%	Multidisciplinary
arXiv	2M+ preprints	No	3 req/s	100%	No	60%	Physics/Math/CS
HAL	1M+ docs	No	10 req/s	70%	No	40%	French research
DBLP	6M+ CS papers	No	10 req/s	0%	No	95%	CS bibliography
ISTEX	25M+ docs	No	10 req/s	95%	No	98%	French archives
OpenAIRE	200M+ records	No	5 req/s	70%	No	75%	EU open-access
ORKG	~55K papers	No	2 req/s	0%	No	80%	Structured CS research
Google Scholar	Unknown	No	—	Varies	Yes	20%	Comprehensive Deprecated

API Details

Semantic Scholar

• Strengths: Excellent citations, AI/ML coverage, free API

• Weaknesses: CS-biased, limited pre-1990 papers

• Use for: AI/ML/CS research, citation networks

• Config key: sem_scholar

OpenAlex

• Strengths: Massive coverage, no key required, institutional data

• Weaknesses: 60% abstract coverage, may lag on recent citations

• Use for: Broad multidisciplinary searches

• Config key: not required

IEEE Xplore

• Strengths: Complete abstracts, engineering focus, standards

• Weaknesses: Daily quota limit (200), API key required

• Use for: Engineering and technology papers

• Config key: ieee

Elsevier

• Strengths: High-quality journals, life sciences, medical

• Weaknesses: API key required, no citations, complex auth

• Use for: Biomedical research

• Config key: elsevier

Springer

• Strengths: Books and chapters, European content

• Weaknesses: API key required, no citations

• Use for: Book chapters, multidisciplinary

• Config key: springer

arXiv

• Strengths: 100% abstracts, free, latest preprints

• Weaknesses: Not peer-reviewed, no citations

• Use for: Cutting-edge physics/math/CS

• Config key: not required

HAL

• Strengths: French research, open access

• Weaknesses: Low DOI coverage (40%), French-focused

• Use for: French and European research

• Config key: not required

DBLP

• Strengths: Complete CS bibliography, high DOI rate (95%)

• Weaknesses: No abstracts (copyright policy), CS-only

• Use for: CS conference papers, bibliographic data

• Config key: not required

ISTEX

• Strengths: Historical archives, 95% abstracts

• Weaknesses: French interface, may require institutional access

• Use for: Historical papers, French archives

• Config key: not required

OpenAIRE

OpenAIRE is the European open-access research gateway, aggregating publications from Horizon 2020 and other EU-funded projects.

• Strengths: 200M+ records, open-access focus, EU-funded research, no key required

• Weaknesses: No citations; some records have limited metadata; max 10K results per query

• Use for: EU-funded research, open-access papers, broad European coverage

• Config key: not required

• API endpoint: https://api.openaire.eu/search/publications

• Response format: XML-over-JSON (data["response"]["results"]["result"]); can return a dict (1 result) or a list — the collector normalises this automatically

• DOI extraction: from the pid list, filtering on @classid == "doi"

• Pagination: 1-based page number; max 10K results per query

ORKG (Open Research Knowledge Graph)

ORKG is a structured knowledge graph for scientific research, maintained by TIB Hannover. It models papers, their contributions, and comparisons in a structured format.

• Strengths: Structured CS/research data, no key required, high DOI coverage

• Weaknesses: Small corpus (~55K papers), no abstracts, no year filter (year filtering applied downstream during aggregation)

• Use for: Structured CS research, contribution-level metadata, knowledge graph studies

• Config key: not required

• API endpoint: https://orkg.org/api/papers

• Response format: data["content"] (list of papers), data["page"]["total_elements"] for total count

• URL fallback: When publication_info.url is empty, URL is set to https://orkg.org/paper/{orkg_id}

• Pagination: 0-based page index

Google Scholar (Deprecated)

⚠️ This API is deprecated and is no longer recommended for use.

• Strengths: Broadest coverage, includes grey literature

• Weaknesses: Web scraping (slow), low DOI coverage (20%), unreliable, requires Tor proxy setup

• Use for: Maximum coverage Not recommended — use OpenAlex or Semantic Scholar instead

API Selection Guide

For AI/CS Research

apis:
  - SemanticScholar
  - DBLP
  - Arxiv
  - ORKG

For Biomedical Research

apis:
  - Elsevier
  - OpenAlex
  - Springer

For Engineering

apis:
  - IEEE
  - Arxiv
  - SemanticScholar

For European/Open-Access Research

apis:
  - OpenAIRE
  - HAL
  - OpenAlex

For Broad Coverage (No Keys Required)

apis:
  - OpenAlex
  - Arxiv
  - DBLP
  - HAL
  - OpenAIRE
  - ORKG

Configuration

API Keys

Get keys from:

• Semantic Scholar

• IEEE

• Elsevier

• Springer

Rate Limits

Conservative defaults in scilex/api.config.yml:

rate_limits:
  SemanticScholar: 1.0
  OpenAlex: 10.0
  IEEE: 10.0
  Elsevier: 6.0
  Springer: 1.5
  Arxiv: 3.0
  HAL: 10.0
  DBLP: 10.0
  Istex: 10.0
  OpenAIRE: 5.0
  ORKG: 2.0

Coverage by Field

• Computer Science: SemanticScholar, DBLP, Arxiv, IEEE, ORKG

• Life Sciences: Elsevier, OpenAlex, Springer

• Engineering: IEEE, Springer, Arxiv

• Physics/Math: Arxiv, OpenAlex, Springer

• Social Sciences: OpenAlex, Springer

• EU-funded Research: OpenAIRE, HAL

• French Research: HAL, ISTEX

Known Limitations

Abstract Availability

• 100%: IEEE, Arxiv

• 95%: Semantic Scholar, ISTEX

• 90%: Springer

• 80%: Elsevier

• 70%: HAL, OpenAIRE

• 60%: OpenAlex

• 0%: DBLP (by policy), ORKG (by design)

DOI Coverage

• 100%: Elsevier

• 98%: Springer, ISTEX

• 95%: IEEE, DBLP

• 90%: OpenAlex

• 85%: Semantic Scholar

• 80%: ORKG

• 75%: OpenAIRE

• 60%: Arxiv

• 40%: HAL

Citation Data Available

• Yes: Semantic Scholar, OpenAlex

• No: All others