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   1482122篇
  免费   34077篇
  国内免费   9476篇
化学   637042篇
晶体学   20007篇
力学   74242篇
综合类   192篇
数学   238369篇
物理学   358320篇
无线电   197503篇
  2021年   15181篇
  2020年   17707篇
  2019年   17888篇
  2016年   29393篇
  2015年   22048篇
  2014年   33245篇
  2013年   79222篇
  2012年   37970篇
  2011年   32427篇
  2010年   38384篇
  2009年   43825篇
  2008年   36214篇
  2007年   32410篇
  2006年   41105篇
  2005年   32027篇
  2004年   34312篇
  2003年   32928篇
  2002年   34309篇
  2001年   33391篇
  2000年   30263篇
  1999年   28506篇
  1998年   27439篇
  1997年   27364篇
  1996年   26888篇
  1995年   24766篇
  1994年   24180篇
  1993年   23503篇
  1992年   23073篇
  1991年   23255篇
  1990年   22073篇
  1989年   21689篇
  1988年   20838篇
  1987年   19645篇
  1986年   18395篇
  1985年   24918篇
  1984年   26169篇
  1983年   22145篇
  1982年   23574篇
  1981年   22767篇
  1980年   22012篇
  1979年   21868篇
  1978年   23165篇
  1977年   22727篇
  1976年   22233篇
  1975年   20891篇
  1974年   20501篇
  1973年   20970篇
  1972年   15199篇
  1968年   12939篇
  1967年   13052篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Siberian Mathematical Journal - Let $ \{(A_{i},B_{i})\}_{i=1}^{m} $ be a set pair system. Füredi, Gyárfás, and Király called it $ 1 $ -cross intersecting if $...  相似文献   
72.
Theoretical and Mathematical Physics - Dynamic systems acting on the plane and possessing the Wada property have been observed. There exist only two topological types, symmetric and antisymmetric,...  相似文献   
73.
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   
74.
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   
75.
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   
76.
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   
77.
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   
78.
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   
79.
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   
80.
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   
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