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   20402篇
  免费   1989篇
  国内免费   1303篇
电工技术   1442篇
综合类   1608篇
化学工业   3766篇
金属工艺   2906篇
机械仪表   1440篇
建筑科学   1111篇
矿业工程   402篇
能源动力   1291篇
轻工业   704篇
水利工程   246篇
石油天然气   323篇
武器工业   178篇
无线电   1343篇
一般工业技术   3162篇
冶金工业   1288篇
原子能技术   188篇
自动化技术   2296篇
  2024年   82篇
  2023年   315篇
  2022年   418篇
  2021年   573篇
  2020年   647篇
  2019年   606篇
  2018年   534篇
  2017年   690篇
  2016年   651篇
  2015年   638篇
  2014年   1030篇
  2013年   1170篇
  2012年   1194篇
  2011年   1583篇
  2010年   1216篇
  2009年   1301篇
  2008年   1186篇
  2007年   1508篇
  2006年   1270篇
  2005年   1031篇
  2004年   952篇
  2003年   794篇
  2002年   733篇
  2001年   613篇
  2000年   527篇
  1999年   440篇
  1998年   384篇
  1997年   310篇
  1996年   247篇
  1995年   218篇
  1994年   201篇
  1993年   136篇
  1992年   108篇
  1991年   77篇
  1990年   72篇
  1989年   62篇
  1988年   37篇
  1987年   21篇
  1986年   16篇
  1985年   26篇
  1984年   21篇
  1983年   16篇
  1982年   8篇
  1981年   8篇
  1980年   8篇
  1979年   3篇
  1978年   2篇
  1964年   3篇
  1956年   1篇
  1951年   3篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
We propose all printed and highly stable organic resistive switching device (ORSD) based on graphene quantum dots (G-QDs) and polyvinylpyrrolidone (PVP) composite for non-volatile memory applications. It is fabricated by sandwiching G-QDs/PVP composite between top and bottom silver (Ag) electrodes on a flexible substrate polyethylene terephthalate (PET) at ambient conditions through a cost effective and eco-friendly electro-hydrodynamic (EHD) technique. Thickness of the active layer is measured around 97 nm. The proposed ORSD is fabricated in a 3 × 3 crossbar array. It operates switching between high resistance state (HRS) and low resistance state (LRS) with OFF/ON ratio ∼14 for more than 500 endurance cycles, and retention time for more than 30 days. The switching voltage for set/reset of the devices is ±1.8 V and the bendability down to 8 mm diameter for 1000 cycles are tested. The elemental composition and surface morphology are characterized by XPS, FE-SEM, and microscope.  相似文献   
2.
3.
To improve the electrochemical properties of rare-earth–Mg–Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the ...  相似文献   
4.
A vacuum-annealed La0.6Ca0.4CoO3−x was consecutively oxygenated in air at temperatures decreasing from 800 to 100 °C, and its electrocatalytic activities for oxygen reduction and evolution were then measured as a function of the oxygenation temperature. The valence of Co cation, changing between +2 and +3, was found susceptible to annealing either in vacuum or air. The catalytic activities initially decrease monotonically as the oxygenation temperature was decreased from 800 to 300 °C, as a result of increasing oxygen content, and then rise abruptly with the oxygen reduction activity reaching a maximum at 200 °C and the oxidation activity at 150 °C. X-ray photoelectron spectroscopy analysis indicated that the enhancements by the low-temperature oxygenation involved increased OH coverage and less charged cations at surface. The results clearly reveal the importance of the post-calcination annealing process for optimizing the performance of La0.6Ca0.4CoO3−x in air electrode applications.  相似文献   
5.
6.
Effect of stoichiometry on microstructures, electrochemical properties and PCT characteristics of the alloys MI(Ni0.71Co0.15-Al0.06Mn0.08)x (MI=Lanthanum-rich Michmetal, x=4.6~5.2) have been investigated. The lattice constants a, c, and cellvolumes of non-stoichiometric alloys are bigger than those of the stoichiometric alloy. With the increasing stoichiometry x,the value of a decreases, and the value of c and cell volume increases except for those of the stoichiometric alloy; the plateaupressure of PCT curve, discharge capacity and cycling stability all increase. The alloy with x=5.2 shows the highest dischargecapacity and the best cycling stability among the studied alloys.  相似文献   
7.
本文用计算机数字模拟方法研究了电活性分子多层Z型L-B膜修饰电极的循环伏安行为。计算了电极与修饰L-B膜分子第一层之间的电荷转移速度常数K_o,L-B膜分子层间的电荷转移速度常数k_i;对峰电位差△E_p及阳极峰面积Q的影响,以及在不同条件下各层分子的氧化态分数随扫描时间的变化。为研究和设计电活性分子修饰电极的实际体系提供了大量数据和信息。  相似文献   
8.
通过对铝材冷轧工艺的分析。研究,以退火工艺中的斑痕为重点,提出采用加氢处理,异构化精制的石蜡基航空煤油组分为基础油,采用不同复合添加剂生产的通用铝冷轧制油完全可以满足客户要求。  相似文献   
9.
10.
A novel finite element model is presented for static and dynamic analysis of composite plates integrated with a laminated piezoelectric layer, a host laminated composite plate and an adhesive layer between them. A new adhesive element is developed which includes both peel and shear effects in the adhesive layer based on first‐order shear deformation plate theory. The thin adhesive layer between the piezoelectric layer and the host plate is modelled by assuming that it carries constant shear and peel strains throughout its thickness. In addition, a weighted static shape control scheme for finding the optimal voltage distribution for static shape control is given. By selecting different weighting matrices, a variety of items such as displacements, slopes, curvatures, strains and even generalized forces, can be included in finding the optimal actuating voltage for static shape control. The present model is validated by comparing with those results available in the literature. The numerical results show that the weighted linear least method can give a satisfactory voltage distribution to best match the desired shape. Copyright © 2004 John Wiley & Sons, Ltd.  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