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   1443173篇
  免费   29923篇
  国内免费   7824篇
化学   739591篇
晶体学   20611篇
力学   76686篇
综合类   108篇
数学   249246篇
物理学   394678篇
  2021年   13622篇
  2020年   16043篇
  2019年   16182篇
  2018年   14602篇
  2016年   29064篇
  2015年   21197篇
  2014年   30767篇
  2013年   74984篇
  2012年   43946篇
  2011年   44984篇
  2010年   40070篇
  2009年   41442篇
  2008年   42528篇
  2007年   39258篇
  2006年   43186篇
  2005年   36207篇
  2004年   36115篇
  2003年   33094篇
  2002年   33527篇
  2001年   34137篇
  2000年   28268篇
  1999年   24219篇
  1998年   21748篇
  1997年   21577篇
  1996年   21461篇
  1995年   19459篇
  1994年   18933篇
  1993年   18508篇
  1992年   19170篇
  1991年   19322篇
  1990年   18519篇
  1989年   18499篇
  1988年   18140篇
  1987年   17965篇
  1986年   16988篇
  1985年   23325篇
  1984年   24289篇
  1983年   20345篇
  1982年   21947篇
  1981年   21128篇
  1980年   20463篇
  1979年   20922篇
  1978年   22035篇
  1977年   21702篇
  1976年   21471篇
  1975年   20232篇
  1974年   19923篇
  1973年   20321篇
  1972年   14806篇
  1967年   12970篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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   
62.
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   
63.
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   
64.
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   
65.
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   
66.
Sohrabi  M. 《Analysis Mathematica》2021,47(2):421-435
Analysis Mathematica - In this paper, we discuss measure theoretic characterizations for Moore-Penrose inverse of Lambert conditional operators, denoted by (MwEMu)?, in some operator classes...  相似文献   
67.
68.
Sun  J.  Yuan  H. 《Experimental Mechanics》2021,61(3):565-580
Experimental Mechanics - Temperature gradients significantly affect the material fatigue process. A reliable and robust test procedure is needed for quantifying the effects of temperature gradients...  相似文献   
69.
Journal of Optimization Theory and Applications - Direct optimization of many-revolution spacecraft trajectories is performed using an unconstrained formulation with many short-arc, embedded...  相似文献   
70.
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