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   79072篇
  免费   7792篇
  国内免费   4204篇
电工技术   5437篇
技术理论   8篇
综合类   6051篇
化学工业   12518篇
金属工艺   4462篇
机械仪表   5332篇
建筑科学   6132篇
矿业工程   2001篇
能源动力   2394篇
轻工业   5735篇
水利工程   1697篇
石油天然气   3539篇
武器工业   689篇
无线电   10066篇
一般工业技术   9982篇
冶金工业   3200篇
原子能技术   966篇
自动化技术   10859篇
  2024年   230篇
  2023年   1224篇
  2022年   2078篇
  2021年   3274篇
  2020年   2465篇
  2019年   2091篇
  2018年   2289篇
  2017年   2559篇
  2016年   2510篇
  2015年   3346篇
  2014年   4111篇
  2013年   4887篇
  2012年   5377篇
  2011年   5838篇
  2010年   5266篇
  2009年   4711篇
  2008年   4793篇
  2007年   4334篇
  2006年   4265篇
  2005年   3615篇
  2004年   2708篇
  2003年   2684篇
  2002年   3028篇
  2001年   2546篇
  2000年   2006篇
  1999年   1678篇
  1998年   1309篇
  1997年   1085篇
  1996年   1024篇
  1995年   858篇
  1994年   700篇
  1993年   520篇
  1992年   398篇
  1991年   315篇
  1990年   236篇
  1989年   187篇
  1988年   158篇
  1987年   90篇
  1986年   69篇
  1985年   47篇
  1984年   33篇
  1983年   17篇
  1982年   30篇
  1981年   25篇
  1980年   18篇
  1979年   9篇
  1976年   8篇
  1975年   7篇
  1959年   6篇
  1951年   3篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
61.
From the perspectives of scientific researches and practical applications, it is desirable to explore high operating temperature ferromagnetic films. The effect of biaxial strain on magnetic properties of (110)-oriented La0.7Sr0.3MnO3 films was studied. High quality La0.7Sr0.3MnO3 films were grown on (110)-oriented perovskite single crystal substrates using pulsed laser deposition, varying substrate-induced misfit strains from ??2.27–0.75%. A remarkable enhancement of Curie temperature has been achieved for (110)-oriented La0.7Sr0.3MnO3 films clamped with small misfit strains (i.e., grown on LAST (110)). The enhanced Curie temperature of (110)-oriented La0.7Sr0.3MnO3 films could be attributed to the misfit strain between the films and the underlying substrates and may have technological implication for applications at high temperature environments.  相似文献   
62.
This paper analyzes the status quo and progress of overseas oil and gas business cooperation built by Chinese oil enterprises in 2017. With the slow recovery of the oil and gas industries as a whole, the overseas oil and gas business of Chinese oil enterprises has continued to grow in size, and all-round cooperation progress was made along the Belt and Road. Breakthroughs were made in oil and gas cooperation between China and the United States. In the meantime, new features have emerged in the overseas cooperation of Chinese enterprises, and a pattern of diversified investors has basically taken shape.  相似文献   
63.
Highly (100)-oriented Ce1-x(Y0.2Zr0.8)xOδ (CYZO) films were prepared on biaxially textured NiW substrates by a chemical solution deposition approach using metal inorganic salts as starting materials. It has been found that both the preferential orientation and surface roughness of CYZO films decrease gradually with increasing of the doping percentage of Y3+ and Zr4+ ions. The epitaxial growth relationship of (220)CYZO//(200)NiW and [00?l]CYZO//[001]NiW was demonstrated by XRD texture measurement as well as atomic resolution STEM observation. XRD, Raman and XPS spectra results indicate that Y3+ and Zr4+ ions were indeed introduced into CeO2 lattice to substitute Ce4+ ions and form cubic fluorite CYZO solid solution. Moreover, CeO2 buffer layer can be endowed a strong enough capability to prevent element diffusion through co-doping of yttrium and zirconium, provided that an optimal doping ratio of them is adopted. This will provide a new approach to fabricating strong-barrier single buffer layer for coated conductor.  相似文献   
64.
65.
Among various drug-delivery systems, core-shell nanoparticles have many advantages. Inspired by nature, biomimetic synthesis has emerged as a new strategy for making core-shell nanoparticles in recent years. Biomimetic mineralization is the process by which living organisms produce minerals based on biomolecule templating that leads to the formation of hierarchically structured organic–inorganic materials. In this minireview, we mainly focus on the synthesis of core-shell nanoparticle drug-delivery systems by biomimetic mineralization. We review various biomimetic mineralization methods for fabricating core-shell nanoparticles including silica-based, calcium-based and other nanoparticles, and their applications in drug delivery. We also summarize strategies for drug loading in the biomolecule-mineralized core-shell NPs. Current challenges and future directions are also discussed.  相似文献   
66.
Near-infrared (NIR) fluorescent probes are very significant for detecting cysteine in biological systems. Herein, we report a highly selective and sensitive NIR turn-on fluorescent probe (BDP-NIR) based on BODIPY with large Stokes shift (105 nm) for detecting Cys. We clarified the sensing mechanism based on the different thiol-induced SNAr substitution/rearrangement reaction of the probe with cysteine and homocysteine/glutathione, which leads to the corresponding amino- and thiol-BODIPY dyes with distinct photophysical properties. Moreover, a novel mechanism of fluorescence quenching was demonstrated by density functional theory calculation. The reason for the fluorescence quenching of the probe might be intersystem crossing (from singlet to triplet excited state). Moreover, BDP-NIR had a high linear dynamic range of 0–500 μM, which was promising for detecting cysteine quantificationally. Significantly, BDP-NIR was capable of sensing endogenous cysteine in living cells and in vivo.  相似文献   
67.
采用基于计算流体力学方法的全尺度数值模拟计算,建立了适用于潮流能水轮机模拟的剪切来流环境,通过数值计算结果,对潮流能水轮机随时间变化的宏观力和流场特征进行了系统分析,探索水轮机在复杂工况下的水动力特性规律。结果表明,水轮机整个叶轮的总体平均受力在剪切流工况中未受到明显影响; 单个叶片的瞬态轴向力系数和瞬态轴向扭矩系数在旋转周期内出现了明显的周期性变化,且周期性变化幅值随转速增大而增大; 非定常的瞬时轴向扭矩和力的周期性振荡容易引起单个叶片的结构性振动,可能对水轮机的机械结构造成影响。  相似文献   
68.
69.
70.
Abstract

Relative populations of four energy-lowest IPR (isolated-pentagon-rule) isomers of Eu@C86 are computed using the Gibbs energy based on characteristics from density functional theory calculations (M06-2X/3-21G?~?SDD entropy term, M06-2X/6-31G*~SDD or B2PLYP(D)/6-31G*~SDD energetics). The calculations confirm that the recently isolated Eu@C1(7)-C86 species is a major isomer in a relevant temperature region. Relationship to the empty C86 cages is discussed, too.  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