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   1155篇
  免费   56篇
  国内免费   103篇
电工技术   25篇
综合类   46篇
化学工业   241篇
金属工艺   187篇
机械仪表   52篇
建筑科学   141篇
矿业工程   22篇
能源动力   38篇
轻工业   60篇
水利工程   7篇
石油天然气   43篇
武器工业   3篇
无线电   55篇
一般工业技术   120篇
冶金工业   71篇
原子能技术   138篇
自动化技术   65篇
  2024年   2篇
  2023年   17篇
  2022年   40篇
  2021年   83篇
  2020年   40篇
  2019年   21篇
  2018年   17篇
  2017年   29篇
  2016年   30篇
  2015年   39篇
  2014年   43篇
  2013年   66篇
  2012年   46篇
  2011年   87篇
  2010年   48篇
  2009年   75篇
  2008年   70篇
  2007年   71篇
  2006年   62篇
  2005年   46篇
  2004年   57篇
  2003年   49篇
  2002年   42篇
  2001年   20篇
  2000年   30篇
  1999年   31篇
  1998年   11篇
  1997年   11篇
  1996年   17篇
  1995年   9篇
  1994年   7篇
  1993年   14篇
  1992年   13篇
  1991年   9篇
  1990年   15篇
  1989年   10篇
  1988年   3篇
  1987年   8篇
  1986年   3篇
  1985年   5篇
  1984年   2篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1978年   2篇
  1977年   3篇
  1976年   2篇
  1975年   2篇
  1963年   1篇
  1954年   1篇
排序方式: 共有1314条查询结果,搜索用时 15 毫秒
81.
A super grid connecting the two shores of the Mediterranean could help Europe meet its targets for integrating renewable energy. This paper assesses the business models for building a platform for wholesale renewable energy trade via electricity corridors linking the two regions of the Mediterranean basin. We demonstrate that the optimal framework for designing the corridor project is a long-term contractual agreement to coordinate bilaterally the necessary investments. Furthermore a hybrid governance structure requiring only limited regulatory adaptation seems to be the most efficient structure for facilitating investment in the corridor's infrastructure.  相似文献   
82.
83.
Yongli Sun  Jianping Yu 《Computing》2006,77(4):379-386
A simple algorithm for finding the implicit equation of a parametric plane curve given by its parametric equations is presented. The algorithm is based on an efficient computation of the Bézout resultant and Lagrange interpolation. One of main features of our approach is the fact that it considerably reduces the problem of computing intermediate expressions.  相似文献   
84.
钛钒基储氢电极合金研究   总被引:3,自引:0,他引:3  
研究了铁钒基储氢电极合金(Ti0.8Zr0 2)(V0.533Mn0.107Cr0.16Ni0 2)x(x=5,6,7)的相结构和电化学性能.XRD分析表明合金主要由六方结构的C14型Laves相和体心立方(BCC)结构的钒基固溶体相所组成.C14型LaveS相及钒基固溶体相的晶胞参数和晶胞体积均随着化学计量比x增加而减小.电化学测试表明当化学计量比由x=5增大到x=7时合金放电容量由394.6mAh/g下降到327.8mAh/g,活化次数略有增加,但循环稳定性和高倍率放电能力明显改善.  相似文献   
85.
HDDR(氢化-歧化-脱氢-重组)工艺是一种用于生产各向异性Nd2Fe14B基磁粉的特殊方法。本文主要研究了添加微量含金元素Ga、采用改进HDDR工艺(即在HD处理及高真空脱氢处理之间加上低真空脱氢处理)对Nd11.2Fe66.5-xCo15.4B6.8Zr0.1Gax(x=0、0.1、0.3、0.5、1.0)合金磁性能的影响规律。结果表明.改进HDDR工艺对于提高磁粉性能,细化主相晶粒尺寸非常有效。微量合金元素Ga的添加可显著地改变材料歧化分解的特征,同时可提高磁粉的磁性能。由改进HDDR工艺制得磁粉主相晶粒尺寸明显小于由传统HDDR工艺制得磁粉主相晶粒尺寸。  相似文献   
86.
A population-wide linkage disequilibrium on bovine chromosome 14 between microsatellite ILSTS039 and DGAT1, a putative quantitative trait locus affecting milk production traits, was found in the Israeli Holstein population. A total of 394 bulls were genotyped for both DGAT1 and ILSTS039, and 1747 cows were genotyped for ILSTS039. The ILSTS039 allele termed "225," and the DGAT1 K allele (substitution of a lysine residue with alanine), were associated with decreased milk production, and increased fat production and fat and protein percent. The number of 225 ILSTS039 and K DGAT1 alleles per individual were the same for 80% of the bulls genotyped. From the effects associated with cows homozygous for the 225 allele, the effect of the quantitative trait locus appears to be approximately codominant. The substitution effect was 0.16% fat. Genotype probabilities for the quantitative gene were determined for the entire Israeli Holstein milk-recorded population, including 507,725 cows and 1442 bulls, using segregation analysis. Overall frequency of the allele that increased fat percent was 8.9% in cows and 15.5% in bulls. The frequency of this allele decreased from 1981 until 1990, from 15 to 5%, and since has increased to 10%. The effects estimated on the population-wide analyses of both cows and bulls were similar to the effect associated with DGAT1 in the daughters of genotyped bulls. Modified animal model evaluations were computed for the entire population with the effect of this gene included in the model. The correlations between the modified and standard animal model evaluations for all traits were > 0.99.  相似文献   
87.
为了了解Fe-Mn基阻尼合金的高温阻尼性能,用真空感应电炉的方法制备了Fe-14.04Mn-0.22C合金.用倒扭摆内耗仪测试了环境温度在23~400℃变化时合金阻尼性能的变化规律,并用热机械分析仪和光学显微镜分析了合金的组织结构及其相变特点.研究结果表明,在常温条件下合金的阻尼性能随扭转应变的增加而呈线性方式增加,扭转应变在1×10-4时,对数衰减率达0.1,且没有出现峰值;随着环境温度的变化,对数衰减曲线与应变的线性关系没有发生改变,但是曲线发生了整体的上下平移;当环境温度低于200℃时,合金的阻尼性能随温度的升高而增加,但当温度达到或超过200℃后,合金的阻尼性能迅速下降,其原因在于合金发生了奥氏体转变(As为270℃),马氏体的百分含量降低,阻尼源减少.  相似文献   
88.
Remarkable progress was made in the development of white-light-emitting diodes (LEDs). White LEDs provided a light element having a semiconductor InGaN light-emitting chip (blue or UV LEDs) and luminescent phosphors. Here we reported the sialon s-phase of (Sr,Eu)2A12Si10N14O4. Eu^2+ activator ions that were substituted for the strontium site represented a new type of yeUow-green phosphor that could be excited by blue LEDs used for application in the fabrication of white LEDs.  相似文献   
89.
用超声化学法制备纳米Fe颗粒包覆的Nd2Fe14B复合粉体,将其在Ar气保护下经放电等离子烧结(SPS),得到Nd2Fe14B/α-Fe纳米晶复合磁体.Fe名义质量分数为5%的烧结磁体具有较高的磁性能:Br=0.86 T,Hci=683.8 kA/m,(BH)max=95.92 kJ/m3.烧结前对复合粉末进行适当的高能球磨,能促进显微组织进一步细化,增强软磁相与硬磁相之间的交换耦合,使相同Fe含量和烧结工艺的磁体Br和(BH)max分别提高到0.94 T和113.6 kJ/m3.  相似文献   
90.
In 1941, the United States Navy intercepted enough Japanese naval messages to predict the attack on Pearl Harbor if the code which protected them had been solved. The messages would have disclosed that, while the Japanese government cynically conducted diplomatic negotiations with the United States, the Japanese Combined Fleet under Admiral Isoroku Yamamoto, beginning as early as September 1941, systematically prepared ships, crews, weapons, tactics, and a complicated fuel supply system for the most ambitious operation ever undertaken by the Japanese navy. Details of Japan's intentions were hidden from Navy cryptanalysts because of limited manpower resources and because all Japanese navy codes were assigned a lower priority than Japanese diplomatic codes and German submarine threat.  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