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   49581篇
  免费   800篇
  国内免费   194篇
化学   26828篇
晶体学   605篇
力学   1537篇
综合类   16篇
数学   5920篇
物理学   15669篇
  2022年   358篇
  2021年   560篇
  2020年   550篇
  2019年   526篇
  2018年   659篇
  2017年   646篇
  2016年   1072篇
  2015年   810篇
  2014年   1030篇
  2013年   2105篇
  2012年   2137篇
  2011年   2390篇
  2010年   1464篇
  2009年   1397篇
  2008年   2094篇
  2007年   2100篇
  2006年   1904篇
  2005年   2403篇
  2004年   2287篇
  2003年   1722篇
  2002年   1264篇
  2001年   1341篇
  2000年   1105篇
  1999年   821篇
  1998年   664篇
  1997年   644篇
  1996年   688篇
  1995年   718篇
  1994年   691篇
  1993年   673篇
  1992年   684篇
  1991年   671篇
  1990年   582篇
  1989年   576篇
  1988年   517篇
  1987年   511篇
  1986年   503篇
  1985年   649篇
  1984年   649篇
  1983年   508篇
  1982年   518篇
  1981年   539篇
  1980年   508篇
  1979年   491篇
  1978年   511篇
  1977年   456篇
  1976年   478篇
  1975年   405篇
  1974年   422篇
  1973年   426篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
1.
Russian Journal of General Chemistry - The review article traces the main trends of the synthetic approach to the solution of the problem of overcoming the resistance of pathogenic bacterial...  相似文献   
2.
3.
Annals of Global Analysis and Geometry - In this paper, we characterize round spheres in the Euclidean space under some suitable conditions on the r-mean curvature.  相似文献   
4.
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   
5.
6.
7.
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation.  相似文献   
8.
9.
10.
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