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   1294783篇
  免费   36673篇
  国内免费   13086篇
化学   644846篇
晶体学   15698篇
力学   75946篇
综合类   426篇
数学   242024篇
物理学   365602篇
  2021年   14927篇
  2020年   17481篇
  2019年   17758篇
  2018年   12194篇
  2016年   28865篇
  2015年   22476篇
  2014年   32723篇
  2013年   77095篇
  2012年   38258篇
  2011年   32265篇
  2010年   37411篇
  2009年   40238篇
  2008年   31356篇
  2007年   25738篇
  2006年   33937篇
  2005年   24846篇
  2004年   26962篇
  2003年   26004篇
  2002年   27499篇
  2001年   25208篇
  2000年   23051篇
  1999年   22265篇
  1998年   21312篇
  1997年   21331篇
  1996年   21581篇
  1995年   19636篇
  1994年   18979篇
  1993年   18390篇
  1992年   17832篇
  1991年   17549篇
  1990年   16750篇
  1989年   16746篇
  1988年   16259篇
  1987年   16318篇
  1986年   15174篇
  1985年   21726篇
  1984年   23147篇
  1983年   19342篇
  1982年   21109篇
  1981年   20350篇
  1980年   19638篇
  1979年   19743篇
  1978年   21178篇
  1977年   20778篇
  1976年   20469篇
  1975年   19132篇
  1974年   18744篇
  1973年   19286篇
  1972年   13825篇
  1967年   12253篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
151.
The health monitoring has been studied to ensure integrity of design of engine structure by detection, quantification, and prediction of damages. Early detection of faults may allow the downtime of maintenance to be rescheduled, thus preventing sudden shutdown of machines. In cylinder pressure developed, vibrations and noise emissions data provide a rich source of information about condition of engines. Monitoring of vibrations and noise emissions are novel non-intrusive methodologies for which positioning of various transducers are important issue. The presented work shows applicability of these diagnosis methodologies adopted in case of diesel engines. The effects of changing various fuel injection parameters was analyzed. Scope of using non-intrusive technique has been analyzed by changing locations of microphone. Novelty of this worklies in exploring signal processing methods for various locations around the engine test set up. Various frequency ranges of contributing noise and vibration sources were identified. Time-Frequency analysis showed the onset of various cyclic. Based on the identification of various frequency bands, it is possible to device suitable filters in order to extract more information.  相似文献   
152.
Herein, we report a Mott-Schottky catalyst by entrapping cobalt nanoparticles inside the N-doped graphene shell (Co@NC). The Co@NC delivered excellent oxygen evolution activity with an overpotential of merely 248 mV at a current density of 10 mA cm–2 with promising long-term stability. The importance of Co encapsulated in NC has further been demonstrated by synthesizing Co nanoparticles without NC shell. The synergy between the hexagonal close-packed (hcp) and face-centered cubic (fcc) Co plays a major role to improve the OER activity, whereas the NC shell optimizes the electronic structure, improves the electron conductivity, and offers a large number of active sites in Co@NC. The density functional theory calculations have revealed that the hcp Co has a dominant role in the surface reaction of electrocatalytic oxygen evolution, whereas the fcc phase induces the built-in electric field at the interfaces with N-doped graphene to accelerate the H+ ion transport.  相似文献   
153.
Crystallography Reports - Two LiInSe2 single crystals, grown under different conditions, have been studied. Characteristics of these crystals for neutron detection have been compared using...  相似文献   
154.
Journal of Radioanalytical and Nuclear Chemistry - In this paper a study for the selection of an NPE (nonylphenol ethoxylates)—free cocktail is discussed in order to be used for our routine...  相似文献   
155.
156.
Radiophysics and Quantum Electronics - A well-known simplified model of turbulent convection from local sources of buoyancy and/or momentum acting for a short time has been developed and...  相似文献   
157.
Gold nanoparticles with different mean sizes were formed on antimony-doped tin oxide nanocrystals by the temperature-varied deposition-precipitation method (Au/ATO NCs). Au/ATO NCs possess strong absorption in the near-infrared region due to Drude excitation in addition to the localized surface plasmon resonance (LSPR) of AuNPs around 530 nm. Au/ATO NCs show thermally activated catalytic activity for the oxidation of cinnamyl alcohol to cinnamaldehyde by hydrogen peroxide. The catalytic activity increases with a decrease in the mean Au particle size (dAu) at 5.3 nm≤dAu≤8.2 nm. Light irradiation (λex >660 nm, ∼0.5 sun) of Au/ATO NCs increases the rate of reaction by more than twice with ∼95 % selectivity. Kinetic analyses indicated that the striking enhancement of the reaction stems from the rise in the temperature near the catalyst surface of ∼30 K due to the photothermal effect of the ATO NCs.  相似文献   
158.
159.
160.
Svetlakova  A. V.  Mendez  M. Sanchez  Tuchin  E. S.  Khodan  A. N.  Traore  M.  Azouani  R.  Kanaev  A.  Tuchin  V. V. 《Optics and Spectroscopy》2021,129(8):846-850
Optics and Spectroscopy - We study the photocatalytic activity of nanocomposites based on θ-phase alumina (Al2O3) with different TiO2 concentrations for heterogeneous photocatalysis and...  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