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   1310428篇
  免费   37801篇
  国内免费   14611篇
化学   660371篇
晶体学   20536篇
力学   75796篇
综合类   513篇
数学   242005篇
物理学   363619篇
  2021年   14654篇
  2020年   17729篇
  2019年   18834篇
  2018年   11982篇
  2016年   29281篇
  2015年   23044篇
  2014年   33352篇
  2013年   78123篇
  2012年   38206篇
  2011年   32175篇
  2010年   38115篇
  2009年   41220篇
  2008年   32384篇
  2007年   26220篇
  2006年   34500篇
  2005年   25492篇
  2004年   27545篇
  2003年   26650篇
  2002年   28659篇
  2001年   25790篇
  2000年   23588篇
  1999年   22071篇
  1998年   20986篇
  1997年   20981篇
  1996年   21242篇
  1995年   19317篇
  1994年   18734篇
  1993年   18181篇
  1992年   17652篇
  1991年   17951篇
  1990年   17189篇
  1989年   17249篇
  1988年   16773篇
  1987年   16806篇
  1986年   15683篇
  1985年   22139篇
  1984年   23511篇
  1983年   19771篇
  1982年   21516篇
  1981年   20767篇
  1980年   20098篇
  1979年   20099篇
  1978年   21518篇
  1977年   21062篇
  1976年   20726篇
  1975年   19393篇
  1974年   19015篇
  1973年   19494篇
  1972年   14018篇
  1967年   12271篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The designs of efficient and inexpensive Pt-based catalysts for methanol oxidation reaction (MOR) are essential to boost the commercialization of direct methanol fuel cells. Here, the highly catalytic performance PtFe alloys supported on multiwalled carbon nanotubes (MWCNTs) decorating nitrogen-doped carbon (NC) have been successfully prepared via co-engineering of the surface composition and electronic structure. The Pt1Fe3@NC/MWCNTs catalyst with moderate Fe3+ feeding content (0.86 mA/mgPt) exhibits 2.26-fold enhancement in MOR mass activity compared to pristine Pt/C catalyst (0.38 mA/mgPt). Furthermore, the CO oxidation initial potential of Pt1Fe3@NC/MWCNTs catalyst is lower relative to Pt/C catalyst (0.71 V and 0.80 V). Benefited from the optimal surface compositions, the anti-corrosion ability of MWCNT, strong electron interaction between PtFe alloys and MWCNTs and the N-doped carbon (NC) layer, the Pt1Fe3@NC/MWCNTs catalyst presents an improved MOR performance and anti-CO poisoning ability. This study would open up new perspective for designing efficient electrocatalysts for the DMFCs field.  相似文献   
62.
Journal of Analytical Chemistry - The present study reports the development of a magnetic polyethylene glycol nanocomposite based on graphite reinforcement carbon paste electrode for the sensitive...  相似文献   
63.
64.

A kinetic study of the effect of thermoheliox (inhalation of a helium and oxygen mixture, 70 °C) on the functional hemodynamics of the human brain by functional magnetic resonance imaging was carried out. The dynamic responses of the BOLD signal were found to be biphasic. An empirical equation describing the first phase of the hemodynamic response to visual stimulus was proposed. It was shown that preliminary inhalation of thermoheliox stimulates the hemodynamic responses by slowing down the vasoconstriction.

  相似文献   
65.
Russian Journal of Organic Chemistry - A highly efficient green protocol has been proposed for the synthesis of symmetrical S-aryl arenesulfonothioates by irradiation of N-hydroxy arenesulfonamides...  相似文献   
66.
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   
67.
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   
68.
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   
69.
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   
70.
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   
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