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   45262篇
  免费   2697篇
  国内免费   44篇
电工技术   395篇
综合类   27篇
化学工业   9226篇
金属工艺   891篇
机械仪表   887篇
建筑科学   1495篇
矿业工程   107篇
能源动力   1084篇
轻工业   7275篇
水利工程   419篇
石油天然气   165篇
武器工业   5篇
无线电   2006篇
一般工业技术   7532篇
冶金工业   9514篇
原子能技术   220篇
自动化技术   6755篇
  2023年   368篇
  2022年   383篇
  2021年   1233篇
  2020年   900篇
  2019年   1084篇
  2018年   1776篇
  2017年   1707篇
  2016年   1822篇
  2015年   1354篇
  2014年   1687篇
  2013年   3316篇
  2012年   2624篇
  2011年   2656篇
  2010年   2084篇
  2009年   1941篇
  2008年   1906篇
  2007年   1770篇
  2006年   1284篇
  2005年   1107篇
  2004年   986篇
  2003年   861篇
  2002年   858篇
  2001年   627篇
  2000年   592篇
  1999年   622篇
  1998年   2894篇
  1997年   1963篇
  1996年   1248篇
  1995年   777篇
  1994年   613篇
  1993年   688篇
  1992年   275篇
  1991年   273篇
  1990年   214篇
  1989年   220篇
  1988年   199篇
  1987年   186篇
  1986年   174篇
  1985年   197篇
  1984年   168篇
  1983年   134篇
  1982年   168篇
  1981年   187篇
  1980年   190篇
  1979年   97篇
  1978年   97篇
  1977年   308篇
  1976年   668篇
  1975年   70篇
  1973年   84篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Passive permeability is a key property in drug disposition and delivery. It is critical for gastrointestinal absorption, brain penetration, renal reabsorption, defining clearance mechanisms and drug-drug interactions. Passive diffusion rate is translatable across tissues and animal species, while the extent of absorption is dependent on drug properties, as well as in vivo physiology/pathophysiology. Design principles have been developed to guide medicinal chemistry to enhance absorption, which combine the balance of aqueous solubility, permeability and the sometimes unfavorable compound characteristic demanded by the target. Permeability assays have been implemented that enable rapid development of structure-permeability relationships for absorption improvement. Future advances in assay development to reduce nonspecific binding and improve mass balance will enable more accurately measurement of passive permeability. Design principles that integrate potency, selectivity, passive permeability and other ADMET properties facilitate rapid advancement of successful drug candidates to patients.  相似文献   
72.
73.
A novel glass-ceramic material based on albite type Na-rich feldspar has been synthesized by conventional ceramic process. High crystallinity, >94%?Vol.% is obtained by fast sintering which allows energy saving processing. Albite is the main crystalline phase and tetragonal SiO2 is a secondary phase. Electrical properties were examined by complex impedance, DC measurements, and dielectric breakdown test. Dielectric characterization shows a non-Debye type dielectric behavior with low dielectric constant, 4.6 at 1?MHz, low dielectric losses, (~10?3 at 1?MHz, and a large dielectric strength, ~60?kV/mm), that it is the largest value reported in ceramic insulators. Those dielectric properties are attained by the low glassy phase content in the samples and their unique micro-nanostructure. All these properties make this novel material a very promising candidate in the market of ceramic electrical insulator, highlighting for high-voltage applications.  相似文献   
74.
The Journal of Supercomputing - Deadlock-free dynamic network reconfiguration process is usually studied from the routing algorithm restrictions and resource reservation perspective. The dynamic...  相似文献   
75.
76.
Abstract

In this work, a new g-C3N4-based Z-scheme with γ-Fe2O3 and β-Ag2Se both n-type semiconductors, and graphite to favor electron exchange is presented. The composite material was studied by XRD, FTIR, UV-Vis, TEM, XPS, TGA, DSC and TOF-SIMS, and the ability of this photocatalytic system to act as a photo-reductant was assessed using crystal violet (CV+) dye. Solar light driven photo-reduction of CV+ in the presence of tri-sodium citrate evidenced a synergistic enhancement of the activity of the composite toward reduction, with ~20 times higher conversion rates per unit of surface area than those of g-C3N4. Photo-oxidation experiments under Xe lamp irradiation in the presence of H2O2 also showed that the AgFeCN composite featured a higher activity (~8×) than g-C3N4. This Z-scheme may deserve further study as a photo-reductant to obtain hydrogen or hydrogenated compounds. Moreover, the use of CV+ may represent a facile procedure that can aid in the selection of new photocatalysts to be used in hydrogen production.  相似文献   
77.
78.
Personal and Ubiquitous Computing - This article presents a study concerning the evaluation of a smart home control system for elderly people with a sample of 10 users in a city in the interior of...  相似文献   
79.
80.
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