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   1474347篇
  免费   32763篇
  国内免费   9173篇
化学   763167篇
晶体学   20838篇
力学   76958篇
综合类   113篇
数学   256591篇
物理学   398616篇
  2021年   14077篇
  2020年   17164篇
  2019年   18249篇
  2018年   15460篇
  2017年   14008篇
  2016年   31032篇
  2015年   23026篇
  2014年   32712篇
  2013年   78276篇
  2012年   46211篇
  2011年   46849篇
  2010年   41990篇
  2009年   43461篇
  2008年   44593篇
  2007年   40761篇
  2006年   44392篇
  2005年   37343篇
  2004年   37086篇
  2003年   33909篇
  2002年   34779篇
  2001年   34496篇
  2000年   28853篇
  1999年   24440篇
  1998年   21944篇
  1997年   21815篇
  1996年   21756篇
  1995年   19647篇
  1994年   19165篇
  1993年   18774篇
  1992年   19291篇
  1991年   19337篇
  1990年   18519篇
  1989年   18473篇
  1988年   18055篇
  1987年   17905篇
  1986年   16969篇
  1985年   23321篇
  1984年   24369篇
  1983年   20406篇
  1982年   22025篇
  1981年   21185篇
  1980年   20554篇
  1979年   20944篇
  1978年   22084篇
  1977年   21708篇
  1976年   21483篇
  1975年   20197篇
  1974年   19886篇
  1973年   20326篇
  1972年   14764篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Numerical Algorithms - In this work, we propose a fractional extension of the one-dimensional nonlinear vibration problem on an elastic string. The fractional problem is governed by a hyperbolic...  相似文献   
62.
Siberian Mathematical Journal - Let $ \{(A_{i},B_{i})\}_{i=1}^{m} $ be a set pair system. Füredi, Gyárfás, and Király called it $ 1 $ -cross intersecting if $...  相似文献   
63.
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   
64.
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   
65.
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   
66.
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   
67.
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   
68.
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   
69.
70.
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   
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