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   1570984篇
  免费   34840篇
  国内免费   10384篇
化学   690277篇
晶体学   20601篇
力学   75637篇
综合类   228篇
数学   243851篇
物理学   381866篇
无线电   203748篇
  2021年   15657篇
  2020年   18130篇
  2019年   18320篇
  2018年   14945篇
  2016年   30853篇
  2015年   22788篇
  2014年   33865篇
  2013年   79880篇
  2012年   42831篇
  2011年   40588篇
  2010年   41573篇
  2009年   46337篇
  2008年   43147篇
  2007年   40291篇
  2006年   46139篇
  2005年   38477篇
  2004年   39288篇
  2003年   36844篇
  2002年   37443篇
  2001年   37349篇
  2000年   32803篇
  1999年   29585篇
  1998年   27747篇
  1997年   27563篇
  1996年   27090篇
  1995年   24828篇
  1994年   24319篇
  1993年   23679篇
  1992年   23729篇
  1991年   23878篇
  1990年   22689篇
  1989年   22253篇
  1988年   21454篇
  1987年   20165篇
  1986年   19010篇
  1985年   25463篇
  1984年   26562篇
  1983年   22428篇
  1982年   23789篇
  1981年   22959篇
  1980年   22218篇
  1979年   22242篇
  1978年   23419篇
  1977年   23067篇
  1976年   22629篇
  1975年   21331篇
  1974年   20916篇
  1973年   21408篇
  1972年   15590篇
  1967年   13365篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
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   
72.
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   
73.
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   
74.
Wireless Personal Communications - Despite its various benefits, the Mobile Ad-hoc Network (MANET) has a number of obstacles due to its mobility, unstable topology, energy efficiency, and other...  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