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   1454657篇
  免费   32048篇
  国内免费   8147篇
化学   621125篇
晶体学   19904篇
力学   73436篇
综合类   104篇
数学   236778篇
物理学   350269篇
无线电   193236篇
  2021年   14663篇
  2020年   17290篇
  2019年   17436篇
  2016年   28797篇
  2015年   21489篇
  2014年   32600篇
  2013年   78297篇
  2012年   36341篇
  2011年   30270篇
  2010年   37356篇
  2009年   42908篇
  2008年   34552篇
  2007年   30814篇
  2006年   39744篇
  2005年   30662篇
  2004年   33274篇
  2003年   32008篇
  2002年   33535篇
  2001年   31619篇
  2000年   29090篇
  1999年   27832篇
  1998年   27053篇
  1997年   27002篇
  1996年   26651篇
  1995年   24497篇
  1994年   23957篇
  1993年   23310篇
  1992年   22596篇
  1991年   22863篇
  1990年   21647篇
  1989年   21330篇
  1988年   20451篇
  1987年   19280篇
  1986年   18050篇
  1985年   24635篇
  1984年   25938篇
  1983年   21997篇
  1982年   23502篇
  1981年   22724篇
  1980年   21973篇
  1979年   21667篇
  1978年   23064篇
  1977年   22577篇
  1976年   22113篇
  1975年   20775篇
  1974年   20376篇
  1973年   20898篇
  1972年   15109篇
  1968年   12837篇
  1967年   12933篇
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
71.
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   
72.
In the periodic table the position of each atom follows the ‘aufbau’ principle of the individual electron shells. The resulting intrinsic periodicity of atomic properties determines the overall behavior of atoms in two-dimensional (2D) bonding and structure formation. Insight into the type and strength of bonding is the key in the discovery of innovative 2D materials. The primary features of 2D bonding and the ensuing monolayer structures of the main-group II–VI elements result from the number of valence electrons and the change of atom size, which determine the type of hybridization. The results reveal the tight connection between strength of bonding and bond length in 2D networks. The predictive power of the periodic table reveals general rules of bonding, the bonding-structure relationship, and allows an assessment of published data of 2D materials.  相似文献   
73.
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   
74.
The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R−BF3). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R−BF3, by cyanostar macrocycles that are size-complementary to the inorganic BF4 progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K+ salts of R−BF3 anions.  相似文献   
75.
Wireless Personal Communications - Besides anti-malware usage for the eradication of malicious attacks, researchers have developed epidemic models in order to gain more insights into the spread...  相似文献   
76.
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   
77.
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   
78.
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   
79.
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   
80.
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   
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