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   1271392篇
  免费   29580篇
  国内免费   7655篇
化学   626046篇
晶体学   19951篇
力学   73521篇
综合类   102篇
数学   237386篇
物理学   351621篇
  2021年   13441篇
  2020年   15874篇
  2019年   15999篇
  2016年   27076篇
  2015年   20549篇
  2014年   30325篇
  2013年   74156篇
  2012年   34402篇
  2011年   28533篇
  2010年   34865篇
  2009年   37850篇
  2008年   28799篇
  2007年   23652篇
  2006年   31838篇
  2005年   23254篇
  2004年   25775篇
  2003年   25049篇
  2002年   26577篇
  2001年   24795篇
  2000年   22523篇
  1999年   21483篇
  1998年   20654篇
  1997年   20707篇
  1996年   20902篇
  1995年   19027篇
  1994年   18457篇
  1993年   17987篇
  1992年   17533篇
  1991年   17865篇
  1990年   17105篇
  1989年   17214篇
  1988年   16731篇
  1987年   16766篇
  1986年   15646篇
  1985年   22145篇
  1984年   23505篇
  1983年   19776篇
  1982年   21518篇
  1981年   20762篇
  1980年   20099篇
  1979年   20099篇
  1978年   21521篇
  1977年   21075篇
  1976年   20734篇
  1975年   19407篇
  1974年   19029篇
  1973年   19504篇
  1972年   14035篇
  1968年   11912篇
  1967年   12288篇
排序方式: 共有10000条查询结果,搜索用时 10 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