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   1331033篇
  免费   44285篇
  国内免费   17555篇
化学   667833篇
晶体学   15060篇
力学   79079篇
综合类   644篇
数学   247236篇
物理学   383021篇
  2021年   16251篇
  2020年   18976篇
  2019年   19465篇
  2018年   13528篇
  2016年   30822篇
  2015年   24233篇
  2014年   35060篇
  2013年   80304篇
  2012年   42140篇
  2011年   36703篇
  2010年   40069篇
  2009年   42921篇
  2008年   34122篇
  2007年   28419篇
  2006年   36401篇
  2005年   26734篇
  2004年   28318篇
  2003年   27026篇
  2002年   28413篇
  2001年   25777篇
  2000年   23629篇
  1999年   23080篇
  1998年   22174篇
  1997年   21628篇
  1996年   20545篇
  1995年   19701篇
  1994年   19179篇
  1993年   18354篇
  1992年   17768篇
  1991年   18023篇
  1990年   17125篇
  1989年   17027篇
  1988年   16494篇
  1987年   16496篇
  1986年   15374篇
  1985年   21877篇
  1984年   23258篇
  1983年   19386篇
  1982年   21164篇
  1981年   20396篇
  1980年   19666篇
  1979年   19748篇
  1978年   21188篇
  1977年   20777篇
  1976年   20471篇
  1975年   19134篇
  1974年   18752篇
  1973年   19290篇
  1972年   13822篇
  1967年   12254篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
71.
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   
72.
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   
73.
Three nonfused ring electron acceptors (NFREAs) TTC6,TT-C8T and TT-TC8 were purposefully designed and synthesized.The molecular geometry can be adjusted by the steric hindrance of lateral substituents.According to the DFT calculations,from TTC6 to TT-C8T and TT-TC8,planarity of the molecular backbone is gradually improved,accompanying with the enhancing of intramolecular charge transfer effect.As for TT-TC8,the two phenyl substituents are almost perpendicular to the molecular backbone,which endues the acceptor with good solubility and suppresses it to form over-aggregation.Multidirectional regular molecular orientation and closer molecular stacking are formed in TT-TC8 film.As a result,TT-TC8 based devices afford the highest PCE of 13.13%,which is much higher than that of TTC6 (4.41%) and TT-C8T (10.42%) and among the highest PCE values based on NFREAs.  相似文献   
74.
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   
75.
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   
76.
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   
77.
Wang  Rong  Li  Xu  Zhou  Youshi  Cao  Shuxuan  Xu  Honghao  Han  Wenjuan  Zhang  Yuxia  Liu  Junhai 《Journal of Russian Laser Research》2022,43(4):476-481
Journal of Russian Laser Research - We demonstrate a passively-mode-locked Pr3+: LuLiF4 laser operated at the 604 nm orange wave-length, using monolayer graphene as a saturable absorber. The...  相似文献   
78.
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   
79.
80.
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