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   1405637篇
  免费   30540篇
  国内免费   8419篇
化学   714767篇
晶体学   20436篇
力学   75937篇
综合类   156篇
数学   246668篇
物理学   386632篇
  2021年   13764篇
  2020年   16214篇
  2019年   16370篇
  2018年   13165篇
  2016年   28555篇
  2015年   21252篇
  2014年   30985篇
  2013年   75281篇
  2012年   42135篇
  2011年   40962篇
  2010年   38856篇
  2009年   40668篇
  2008年   39356篇
  2007年   35390篇
  2006年   41167篇
  2005年   33366篇
  2004年   33991篇
  2003年   31496篇
  2002年   32325篇
  2001年   32243篇
  2000年   27224篇
  1999年   23805篇
  1998年   21655篇
  1997年   21519篇
  1996年   21479篇
  1995年   19513篇
  1994年   18950篇
  1993年   18493篇
  1992年   18814篇
  1991年   19041篇
  1990年   18173篇
  1989年   18149篇
  1988年   17741篇
  1987年   17577篇
  1986年   16597篇
  1985年   22985篇
  1984年   24074篇
  1983年   20209篇
  1982年   21878篇
  1981年   21045篇
  1980年   20379篇
  1979年   20688篇
  1978年   21907篇
  1977年   21523篇
  1976年   21318篇
  1975年   20030篇
  1974年   19748篇
  1973年   20196篇
  1972年   14644篇
  1967年   12799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