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   112113篇
  免费   8434篇
  国内免费   4271篇
电工技术   5899篇
技术理论   11篇
综合类   6608篇
化学工业   19011篇
金属工艺   5957篇
机械仪表   6730篇
建筑科学   8653篇
矿业工程   3088篇
能源动力   3110篇
轻工业   6636篇
水利工程   1730篇
石油天然气   6222篇
武器工业   698篇
无线电   14051篇
一般工业技术   14296篇
冶金工业   5946篇
原子能技术   1252篇
自动化技术   14920篇
  2024年   432篇
  2023年   1760篇
  2022年   2908篇
  2021年   4016篇
  2020年   3065篇
  2019年   2601篇
  2018年   2999篇
  2017年   3392篇
  2016年   2942篇
  2015年   3881篇
  2014年   4915篇
  2013年   6287篇
  2012年   6616篇
  2011年   7218篇
  2010年   6290篇
  2009年   6213篇
  2008年   6207篇
  2007年   5779篇
  2006年   6061篇
  2005年   5434篇
  2004年   3720篇
  2003年   3221篇
  2002年   2862篇
  2001年   2770篇
  2000年   2882篇
  1999年   3396篇
  1998年   2919篇
  1997年   2557篇
  1996年   2294篇
  1995年   1924篇
  1994年   1561篇
  1993年   1223篇
  1992年   966篇
  1991年   744篇
  1990年   605篇
  1989年   503篇
  1988年   391篇
  1987年   296篇
  1986年   208篇
  1985年   177篇
  1984年   109篇
  1983年   81篇
  1982年   87篇
  1981年   57篇
  1980年   46篇
  1979年   32篇
  1978年   25篇
  1977年   25篇
  1976年   40篇
  1973年   11篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
1.
Feature-based methods have been developed in the past decades for the registration of optical satellite images. However, it is still a challenging problem to handle well the registration between medium and high spatial resolution images due to the large difference of the spatial structural features and local details for the same objects. In this study, an automated co-registration technique is proposed that integrates an improved SIFT (I-SIFT) and a novel matching strategy called spatial consistency constraints (SCC) to cope with the large difference in spatial resolutions between the image pair. Three constraints on angle, distance, and ratio are introduced to re the initial matching features obtained by I-SIFT. Three groups of experiments were conducted to validate the effectiveness of the proposed method. The experiments used high resolution multispectral and panoramic SPOT 5/6 images and Landsat 5/8 orthorectification images. Experimental results show that the registration error lies in about 1 pixel of high-resolution images and demonstrate that the proposed I-SIFT-SCC approach is suitable for fine registration of optical satellite images from medium spatial resolution to high spatial resolution with resolution ratio up to 6.  相似文献   
2.
3.
4.
Malondialdehyde (MDA) was selected to represent a secondary by-product of lipid peroxidation during rice ageing. This study aimed to investigate the effects of MDA modification on the structural characteristics of rice protein. The results showed that as MDA concentration increased, rice protein carbonyl and disulphide groups increased, but sulphydryl content decreased. The blue shift of maximum fluorescence peak, the decrease of rice protein intrinsic fluorescence intensity and the reduction of surface hydrophobicity indicated the formation of protein aggregates caused by MDA oxidative modification. The results of molecular weight distribution and particle size distribution showed that MDA modification resulted in the formation of soluble protein aggregates, and the decrease of rice protein solubility indicated that insoluble protein aggregates were formed. Results of protein electrophoresis showed that MDA modification contributed to rice protein aggregation via non-disulphide covalent bonds. The results showed that rice protein gradually aggregated with increasing MDA concentration.  相似文献   
5.
Yan  Jing  Zhu  Rongying  Wu  Fan  Zhao  Ziyin  Ye  Huan  Hou  Mengying  Liu  Yong  Yin  Lichen 《Nano Research》2020,13(10):2706-2715
Nano Research - Insufficient intratumoral penetration greatly hurdles the anticancer performance of nanomedicine. To realize highly efficient tumor penetration in a precisely and spatiotemporally...  相似文献   
6.
7.
Wu  Li  Li  Jing  Fu  Caixia  Kühn  Bernd  Wang  Xiaolin 《Magma (New York, N.Y.)》2019,32(4):501-509
Magnetic Resonance Materials in Physics, Biology and Medicine - To investigate the value of using diffusion-weighted imaging (DWI) and intravoxel incoherent motion DWI (IVIM-DWI) to assess the...  相似文献   
8.
吴志民  张朝川 《电子测试》2020,(9):108-109,111
针对传统低压回路电阻测试仪只能在被测设备停电时使用的一大限制,本文提出并设计了一种新型低压回路电阻测试仪。该仪器可在低压设备运行状态下对其回路电阻进行测量,在保证测量精度的前提下减少了设备停电率,大大提高了工作效率。  相似文献   
9.
Engineering novel Sn-based bimetallic materials could provide intriguing catalytic properties to boost the electrochemical CO2 reduction. Herein, the first synthesis of homogeneous Sn1−xBix alloy nanoparticles (x up to 0.20) with native Bi-doped amorphous SnOx shells for efficient CO2 reduction is reported. The Bi-SnOx nanoshells boost the production of formate with high Faradaic efficiencies (>90%) over a wide potential window (−0.67 to −0.92 V vs RHE) with low overpotentials, outperforming current tin oxide catalysts. The state-of-the-art Bi-SnOx nanoshells derived from Sn0.80Bi0.20 alloy nanoparticles exhibit a great partial current density of 74.6 mA cm−2 and high Faradaic efficiency of 95.8%. The detailed electrocatalytic analyses and corresponding density functional theory calculations simultaneously reveal that the incorporation of Bi atoms into Sn species facilitates formate production by suppressing the formation of H2 and CO.  相似文献   
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