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   512190篇
  免费   5328篇
  国内免费   1517篇
化学   230103篇
晶体学   6921篇
力学   21040篇
综合类   14篇
数学   52209篇
物理学   144429篇
无线电   64319篇
  2021年   4283篇
  2020年   4682篇
  2019年   5156篇
  2018年   6822篇
  2017年   6965篇
  2016年   9993篇
  2015年   5625篇
  2014年   9545篇
  2013年   22276篇
  2012年   16909篇
  2011年   20573篇
  2010年   15371篇
  2009年   16036篇
  2008年   19941篇
  2007年   20597篇
  2006年   19129篇
  2005年   17118篇
  2004年   15845篇
  2003年   14180篇
  2002年   14096篇
  2001年   16050篇
  2000年   12605篇
  1999年   10086篇
  1998年   8829篇
  1997年   8574篇
  1996年   7969篇
  1995年   7210篇
  1994年   7079篇
  1993年   6772篇
  1992年   7418篇
  1991年   7549篇
  1990年   7069篇
  1989年   6826篇
  1988年   6459篇
  1987年   5993篇
  1986年   5618篇
  1985年   7079篇
  1984年   7199篇
  1983年   6081篇
  1982年   6148篇
  1981年   5788篇
  1980年   5641篇
  1979年   5974篇
  1978年   6064篇
  1977年   5973篇
  1976年   5962篇
  1975年   5658篇
  1974年   5604篇
  1973年   5612篇
  1972年   3939篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Russian Journal of Organic Chemistry - A highly efficient green protocol has been proposed for the synthesis of symmetrical S-aryl arenesulfonothioates by irradiation of N-hydroxy arenesulfonamides...  相似文献   
22.
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   
23.
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   
24.
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   
25.
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   
26.
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically...  相似文献   
27.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is...  相似文献   
28.
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   
29.
30.
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   
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