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   1421586篇
  免费   29897篇
  国内免费   7836篇
化学   722250篇
晶体学   20684篇
力学   76599篇
综合类   107篇
数学   247662篇
物理学   392017篇
  2021年   13613篇
  2020年   16048篇
  2019年   16180篇
  2018年   15129篇
  2017年   13447篇
  2016年   29205篇
  2015年   21180篇
  2014年   30715篇
  2013年   74872篇
  2012年   42510篇
  2011年   43186篇
  2010年   39938篇
  2009年   41544篇
  2008年   41027篇
  2007年   37627篇
  2006年   40938篇
  2005年   34701篇
  2004年   34537篇
  2003年   31775篇
  2002年   32204篇
  2001年   32701篇
  2000年   27372篇
  1999年   23766篇
  1998年   21539篇
  1997年   21416篇
  1996年   21399篇
  1995年   19445篇
  1994年   18885篇
  1993年   18506篇
  1992年   18962篇
  1991年   19140篇
  1990年   18328篇
  1989年   18307篇
  1988年   17873篇
  1987年   17813篇
  1986年   16757篇
  1985年   23119篇
  1984年   24156篇
  1983年   20219篇
  1982年   21822篇
  1981年   21033篇
  1980年   20362篇
  1979年   20766篇
  1978年   21902篇
  1977年   21558篇
  1976年   21310篇
  1975年   20020篇
  1974年   19668篇
  1973年   20089篇
  1972年   14602篇
排序方式: 共有10000条查询结果,搜索用时 31 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