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   1433739篇
  免费   44475篇
  国内免费   17492篇
化学   728376篇
晶体学   21298篇
力学   80985篇
综合类   625篇
数学   253357篇
物理学   411065篇
  2021年   16551篇
  2020年   19018篇
  2019年   19498篇
  2018年   16607篇
  2017年   15111篇
  2016年   32318篇
  2015年   24619篇
  2014年   35249篇
  2013年   80657篇
  2012年   46647篇
  2011年   45112篇
  2010年   43185篇
  2009年   45312篇
  2008年   40895篇
  2007年   36508篇
  2006年   40830篇
  2005年   32865篇
  2004年   32974篇
  2003年   30451篇
  2002年   31189篇
  2001年   30594篇
  2000年   26394篇
  1999年   24366篇
  1998年   22684篇
  1997年   22542篇
  1996年   22765篇
  1995年   20509篇
  1994年   19945篇
  1993年   19160篇
  1992年   19149篇
  1991年   19334篇
  1990年   18399篇
  1989年   18249篇
  1988年   17689篇
  1987年   17648篇
  1986年   16600篇
  1985年   22936篇
  1984年   24061篇
  1983年   20167篇
  1982年   21791篇
  1981年   20996篇
  1980年   20316篇
  1979年   20527篇
  1978年   21760篇
  1977年   21360篇
  1976年   21073篇
  1975年   19727篇
  1974年   19380篇
  1973年   19824篇
  1972年   14311篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
61.
Chemistry of Heterocyclic Compounds - 2-Imino-2,5-dihydrofurans are a highly valuable class of heterocyclic compounds that show versatile biological activity and are used in diverse fields of...  相似文献   
62.
Low-flow chromatography has a rich history of innovation but has yet to reach widespread implementation in bioanalytical applications. Improvements in pump technology, microfluidic connections, and nano-electrospray sources for MS have laid the groundwork for broader application, and innovation in this space has accelerated in recent years. This article reviews the instrumentation used for nano-flow LC, the types of columns employed, and strategies for multidimensionality of separations, which are key to the future state of the technique to the high-throughput needs of modern bioanalysis. An update of the current applications where nano-LC is widely used, such as proteomics and metabolomics, is discussed. But the trend toward biopharmaceutical development of increasingly complex, targeted, and potent therapeutics for the safe treatment of disease drives the need for ultimate selectivity and sensitivity of our analytical platforms for targeted quantitation in a regulated space. The selectivity needs are best addressed by mass spectrometric detection, especially at high resolutions, and exquisite sensitivity is provided by nano-electrospray ionization as the technology continues to evolve into an accessible, robust, and easy-to-use platform.  相似文献   
63.
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   
64.
Hua  Saixiang  Zhu  Huichao  Wang  Xiao  Wu  Mingyuan  Wu  Qingyun  Liu  Jiuyi  Yang  Jianjun  Zhang  Jianan 《Cellulose (London, England)》2022,29(13):7465-7475
Cellulose - Ultraviolet (UV) protective cotton fabric is a convenient and reliable way to protect human body from sunlight. Herein, a polymerizable UV-absorber,...  相似文献   
65.
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   
66.

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   
67.
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   
68.
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   
69.
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   
70.
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   
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