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   1310778篇
  免费   29643篇
  国内免费   7703篇
化学   650292篇
晶体学   20251篇
力学   74195篇
综合类   102篇
数学   240283篇
物理学   363001篇
  2021年   13473篇
  2020年   15922篇
  2019年   16056篇
  2016年   27586篇
  2015年   20678篇
  2014年   30403篇
  2013年   74338篇
  2012年   36607篇
  2011年   32220篇
  2010年   36173篇
  2009年   38774篇
  2008年   32146篇
  2007年   27312篇
  2006年   34409篇
  2005年   26483篇
  2004年   28266篇
  2003年   26984篇
  2002年   28221篇
  2001年   26659篇
  2000年   23607篇
  1999年   21941篇
  1998年   20842篇
  1997年   20834篇
  1996年   21066篇
  1995年   19126篇
  1994年   18577篇
  1993年   18128篇
  1992年   17826篇
  1991年   18131篇
  1990年   17371篇
  1989年   17415篇
  1988年   16980篇
  1987年   16997篇
  1986年   15881篇
  1985年   22334篇
  1984年   23668篇
  1983年   19936篇
  1982年   21623篇
  1981年   20860篇
  1980年   20192篇
  1979年   20285篇
  1978年   21671篇
  1977年   21220篇
  1976年   20902篇
  1975年   19604篇
  1974年   19278篇
  1973年   19736篇
  1972年   14225篇
  1968年   12080篇
  1967年   12439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