首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   377779篇
  免费   3843篇
  国内免费   1131篇
化学   164455篇
晶体学   5374篇
力学   15531篇
综合类   7篇
数学   38461篇
物理学   109712篇
无线电   49213篇
  2021年   3495篇
  2020年   3775篇
  2019年   4241篇
  2018年   5719篇
  2017年   5870篇
  2016年   8060篇
  2015年   4368篇
  2014年   7657篇
  2013年   17086篇
  2012年   13090篇
  2011年   15664篇
  2010年   11960篇
  2009年   12444篇
  2008年   15110篇
  2007年   15626篇
  2006年   14510篇
  2005年   12756篇
  2004年   11901篇
  2003年   10689篇
  2002年   10592篇
  2001年   12293篇
  2000年   9545篇
  1999年   7633篇
  1998年   6594篇
  1997年   6403篇
  1996年   5921篇
  1995年   5219篇
  1994年   5137篇
  1993年   4979篇
  1992年   5405篇
  1991年   5514篇
  1990年   5232篇
  1989年   4959篇
  1988年   4638篇
  1987年   4424篇
  1986年   4111篇
  1985年   5140篇
  1984年   5181篇
  1983年   4311篇
  1982年   4315篇
  1981年   4019篇
  1980年   3907篇
  1979年   4151篇
  1978年   4122篇
  1977年   4114篇
  1976年   4062篇
  1975年   3878篇
  1974年   3776篇
  1973年   3816篇
  1972年   2730篇
排序方式: 共有10000条查询结果,搜索用时 333 毫秒
21.
Mathematical Notes - Subspaces of the space of analytic functions on a convex domain in the complex plane that are invariant with respect to the differentiation operator are studied. The problem of...  相似文献   
22.
The requirement of green and sustainable materials to prepare heterogeneous catalysts has intensified for practical reasons over the past few decades. Carbohydrates are possibly the most plentiful and renewable organic materials in nature with inimitable physiochemical properties, plausible low-cost and large-scale production, and sustainability features could be exploited in the generation of nanostructured heterogeneous catalysts. This review article outlines the organic transformations catalyzed by diverse carbohydrate-based nanostructured catalysts in greener and environmentally friendly processes. Selected examples are highlighted for a variety of organic reactions exploiting the proposed catalysts’ reactivity and reusability, and interactions with the intrinsic nature of the applied carbohydrate supports; advantages and speculated challenges of the introduced catalysts are deliberated as well.  相似文献   
23.
Telecommunication Systems - Energy saving in User Equipment (UE) is one of the important issues for limited sources of power in the device. It is critical for the UE to maximize its energy...  相似文献   
24.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
25.
Journal of Communications Technology and Electronics - In recent years, there has been a rapid improvement in photonics products due to the use of multilayer heterostructures grown on the basis of...  相似文献   
26.
27.
Russian Physics Journal - The temperature dependences of the linear dielectric permittivity ε′ and the third harmonic coefficient γ3ω for nanocomposites obtained by embedding a...  相似文献   
28.
Recent advancements in isolation and stacking of layered van der Waals materials have created an unprecedented paradigm for demonstrating varieties of 2D quantum materials. Rationally designed van der Waals heterostructures composed of monolayer transition-metal dichalcogenides (TMDs) and few-layer hBN show several unique optoelectronic features driven by correlations. However, entangled superradiant excitonic species in such systems have not been observed before. In this report, it is demonstrated that strong suppression of phonon population at low temperature results in a formation of a coherent excitonic-dipoles ensemble in the heterostructure, and the collective oscillation of those dipoles stimulates a robust phase synchronized ultra-narrow band superradiant emission even at extremely low pumping intensity. Such emitters are in high demand for a multitude of applications, including fundamental research on many-body correlations and other state-of-the-art technologies. This timely demonstration paves the way for further exploration of ultralow-threshold quantum-emitting devices with unmatched design freedom and spectral tunability.  相似文献   
29.

We show that near periodic rivet chains that connect two Kirchhoff plates and are modeled by point Sobolev transmission conditions, Rayleigh waves arise, propagate along the chains, and decay exponentially in the orthogonal direction. Under additional geometric conditions we discover the standing (periodic) waves that carry no energy.

  相似文献   
30.
Optics and Spectroscopy - The current–voltage characteristics and photocurrent of “monolithic” diode optical pairs optically coupled by a substrate made of InAs common for them...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号