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   1282875篇
  免费   35289篇
  国内免费   11916篇
化学   636992篇
晶体学   15532篇
力学   75436篇
综合类   304篇
数学   240335篇
物理学   361481篇
  2021年   14551篇
  2020年   17135篇
  2019年   17439篇
  2018年   11905篇
  2016年   28479篇
  2015年   21928篇
  2014年   32140篇
  2013年   76540篇
  2012年   37055篇
  2011年   31062篇
  2010年   36667篇
  2009年   39564篇
  2008年   30561篇
  2007年   24984篇
  2006年   33303篇
  2005年   24128篇
  2004年   26487篇
  2003年   25614篇
  2002年   27256篇
  2001年   24782篇
  2000年   22689篇
  1999年   22006篇
  1998年   21137篇
  1997年   21131篇
  1996年   21428篇
  1995年   19517篇
  1994年   18814篇
  1993年   18281篇
  1992年   17772篇
  1991年   17448篇
  1990年   16661篇
  1989年   16709篇
  1988年   16225篇
  1987年   16276篇
  1986年   15143篇
  1985年   21710篇
  1984年   23117篇
  1983年   19320篇
  1982年   21102篇
  1981年   20345篇
  1980年   19628篇
  1979年   19732篇
  1978年   21177篇
  1977年   20771篇
  1976年   20460篇
  1975年   19127篇
  1974年   18742篇
  1973年   19285篇
  1972年   13817篇
  1967年   12250篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
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   
72.
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   
73.
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   
74.
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   
75.
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   
76.
77.
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   
78.
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   
79.
Russian Physics Journal - The temperature dependences of the linear dielectric permittivity ε′ and the third harmonic coefficient γ3ω for nanocomposites obtained by embedding a...  相似文献   
80.
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