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   541609篇
  免费   6654篇
  国内免费   1713篇
化学   281631篇
晶体学   8136篇
力学   23992篇
综合类   9篇
数学   66970篇
物理学   169238篇
  2021年   4451篇
  2020年   4947篇
  2019年   5478篇
  2018年   7222篇
  2017年   7387篇
  2016年   10850篇
  2015年   6687篇
  2014年   10468篇
  2013年   25911篇
  2012年   19431篇
  2011年   23516篇
  2010年   16502篇
  2009年   16186篇
  2008年   21149篇
  2007年   21148篇
  2006年   19453篇
  2005年   17327篇
  2004年   15836篇
  2003年   13982篇
  2002年   13867篇
  2001年   15895篇
  2000年   12040篇
  1999年   9420篇
  1998年   7882篇
  1997年   7783篇
  1996年   7397篇
  1995年   6604篇
  1994年   6490篇
  1993年   6570篇
  1992年   7012篇
  1991年   7091篇
  1990年   6829篇
  1989年   6703篇
  1988年   6508篇
  1987年   6543篇
  1986年   6210篇
  1985年   8195篇
  1984年   8356篇
  1983年   6899篇
  1982年   7304篇
  1981年   6976篇
  1980年   6811篇
  1979年   7036篇
  1978年   7315篇
  1977年   7133篇
  1976年   7250篇
  1975年   6675篇
  1974年   6748篇
  1973年   7030篇
  1972年   4685篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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   
22.

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   
23.
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   
24.
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   
25.
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   
26.
27.
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   
28.

We show that near periodic rivet chains that connect two Kirchhoff plates and are modeled by point Sobolev transmission conditions, Rayleigh waves arise, propagate along the chains, and decay exponentially in the orthogonal direction. Under additional geometric conditions we discover the standing (periodic) waves that carry no energy.

  相似文献   
29.
Acta Mathematica Hungarica - Minkowski’s classical existence theorem provides necessary and sufficient conditions for a Borel measure on the unit sphere of Euclidean space to be the surface...  相似文献   
30.
Optics and Spectroscopy - The current–voltage characteristics and photocurrent of “monolithic” diode optical pairs optically coupled by a substrate made of InAs common for them...  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