全文获取类型
收费全文 | 241506篇 |
免费 | 24473篇 |
国内免费 | 10259篇 |
专业分类
电工技术 | 24467篇 |
技术理论 | 33篇 |
综合类 | 23689篇 |
化学工业 | 28086篇 |
金属工艺 | 10410篇 |
机械仪表 | 12893篇 |
建筑科学 | 32040篇 |
矿业工程 | 13433篇 |
能源动力 | 9012篇 |
轻工业 | 17514篇 |
水利工程 | 10976篇 |
石油天然气 | 12336篇 |
武器工业 | 3371篇 |
无线电 | 16792篇 |
一般工业技术 | 17850篇 |
冶金工业 | 11978篇 |
原子能技术 | 1870篇 |
自动化技术 | 29488篇 |
出版年
2025年 | 65篇 |
2024年 | 4115篇 |
2023年 | 4354篇 |
2022年 | 6546篇 |
2021年 | 8561篇 |
2020年 | 8397篇 |
2019年 | 6490篇 |
2018年 | 5944篇 |
2017年 | 7343篇 |
2016年 | 8589篇 |
2015年 | 9226篇 |
2014年 | 16141篇 |
2013年 | 14276篇 |
2012年 | 17344篇 |
2011年 | 18949篇 |
2010年 | 13853篇 |
2009年 | 14068篇 |
2008年 | 12941篇 |
2007年 | 15685篇 |
2006年 | 14270篇 |
2005年 | 12398篇 |
2004年 | 10243篇 |
2003年 | 8859篇 |
2002年 | 7218篇 |
2001年 | 5960篇 |
2000年 | 5094篇 |
1999年 | 4017篇 |
1998年 | 2852篇 |
1997年 | 2489篇 |
1996年 | 2020篇 |
1995年 | 1685篇 |
1994年 | 1394篇 |
1993年 | 998篇 |
1992年 | 808篇 |
1991年 | 571篇 |
1990年 | 488篇 |
1989年 | 461篇 |
1988年 | 251篇 |
1987年 | 198篇 |
1986年 | 166篇 |
1985年 | 187篇 |
1984年 | 135篇 |
1983年 | 114篇 |
1982年 | 61篇 |
1981年 | 78篇 |
1980年 | 84篇 |
1979年 | 37篇 |
1978年 | 21篇 |
1977年 | 23篇 |
1959年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
水岸彩色图像边缘提取是图像基础处理的难题。阐述了所提出的方法:依据纵向灰度最大差之和与图像灰度平均值间的模糊关系确定梯度阈值;运用平均值与中值协调方式滤波,在求中值群时拓展了Paeth提出的简化求中值算法以提高运算速度;在边界提取时选取有一定间距的像素分别计算三原色梯度,把其中绝对值最大的梯度作为边界存在的判据之一,同时根据二阶导数符号变化提取边界。算法对不同时刻和不同天气状况下的大量图像进行处理,结果表明能较好地自适应调整阈值,提取出的边界受噪声等影响产生的伪边界点和边界断点少,提高了边界点的有效性和连续性。它适用于对水岸彩色图像的概括性识别前期处理。 相似文献
992.
WangAiming ZhuMinhui 《电子科学学刊(英文版)》2004,21(1):64-71
Synthetic Aperture Radar (SAR) imaging of ocean surface features is studied.The simulation of the turbulent and vortical features generated by a moving ship and SAR imaging of these wakes is carried out.The turbulent wake damping the ocean surface capillary waves may be partially responsible for the suppression of surface waves near the ship track.The vortex pair generating a change in the lateral flow field behind the ship may be partially responsible for an enhancement of the waves near the edges of the smooth area.These hydrodynamic phenomena as well as the changes of radar backscatter generated by turbulence and vortex are simulated.An SAR imaging model is then used on such ocean surface features to provide SAR images.Comparison of two ships‘simulated SAR images shows that the wake features are different for various ship parameters. 相似文献
993.
994.
In order to prevent and eliminate the asphaltene precipitation during gas flooding, the rules of the changes of the pressure under different conditions are systematically studied by the laser solid detection system, the light transmission method, and the P–T phase diagram when the asphaltene precipitation occurs. When the pressure is reducing to a certain value, the penetrating light intensity of the crude oil is markedly decreased, which shows that the pressure at this point is the pressure of the onset of asphaltene precipitation (AOPP). The AOPP value decreases with an increase in the temperature. During gas flooding, the AOPP value increases with an increase in the content of gas in the crude oil, and these two nearly do have a linear relationship. According to the P–T phase behaviors of the gas–crude oil system, with an increase in the content of gas in the crude oil, the asphaltene precipitation envelope curve (APE) is gradually moved up, which shows that the possibility of asphaltene precipitation is much higher. During oil production, for the oil reservoirs with rich asphaltene, the production pressure drop should be kept a small value to ensure that the flowing bottom-hole pressure is higher than AOPP and it is necessary to help complement producing energy timely by using water injection, gas injection, etc. Besides, according to the intersection of T–P curve and APE curve in the P–T phase diagram, the location where the asphaltene precipitation occurs in the wellbore can be roughly predicted. The experimental results can provide the theoretical foundation for taking measures to prevent and eliminate the asphaltene precipitation. 相似文献
995.
分析了硬脆性泥页岩井壁失稳的原因,介绍了纳米材料特点及其应用,并概述了国内外钻井液用纳米封堵剂的研究进展,包括有机纳米封堵剂、无机纳米封堵剂、有机/无机纳米封堵剂,以及纳米封堵剂现场应用案例。笔者认为:利用无机纳米材料刚性特征以及有机聚合物可任意变形、支化成膜等特性,形成的一种核壳结构的无机/聚合物类纳米封堵剂,能够很好地分散到钻井液中,且对钻井液黏度和切力影响较小,这种类型的纳米封堵剂能够在低浓度下封堵泥页岩孔喉,建立一种疏水型且具有一定强度的泥页岩人工井壁,这不仅能够阻止钻井液侵入,而且还能提高地层承压能力,无机纳米材料与有机聚合物的结合是未来钻井液防塌剂的发展方向。 相似文献
996.
根据国家统计局提供的数据,对2017年1—8月钢管行业运行情况进行了总体介绍,并就钢管产量、表观消费量、价格以及钢管进出口情况进行了统计分析。就2017年我国钢管行业的运行特点及取得的主要成绩做了详尽的阐述,结合目前钢铁行业的整体情况,指出了2017年钢管行业应重点关注的若干问题,对我国推进供给侧结构性改革新形势下,加快钢管行业转型升级,促进行业健康稳定发展具有很好的指导意义。 相似文献
997.
998.
《Food Control》2017
Sprout-related outbreaks of foodborne illnesses are increasingly becoming a food safety concern. Different pathogenic microorganisms that originate from sprout seeds are known to play a crucial role in the pathogenesis of such outbreaks. Therefore, in order to decontaminate and also to enhance the germination of seeds, the applications of non-thermal plasma based techniques are increasingly being investigated in the field of agricultural science as an alternative to conventional pre-germination treatments. This work was aimed to evaluate the effectiveness of corona discharge plasma jet (CDPJ) for microbial decontamination of rapeseed seeds, and also studied the plasma treatment effect on the seed germination and physicochemical properties of sprouts (grown from the plasma-treated seeds). Aerobic bacteria, molds and yeast, Bacillus cereus, Escherichia coli, Salmonella spp. were detected as contaminants in the seeds. All the detected microorganisms were reduced in the range of 1.2–2.2 log CFU/g upon the CDPJ treatment for 3 min. The inactivation patterns are better explained using pseudo-first-order kinetics. The plasma treatment of seeds up to 2 min showed positive effects on their germination rate and seedling growth. Physicochemical and sensory characteristics of rape sprouts were unaffected due to the CDPJ treatment of their respective seeds. Therefore, the CDPJ treatment of rapeseed seeds has not only reduced the seed microbial load, but also contributed to the enhancement of their germination rate and seedling growth, without adversely affecting the physicochemical and sensory characteristics of their corresponding sprouts. 相似文献
999.
本文给出了CMOS倒相器的高温等效电路,分析了它的高温直流传输特性和瞬态特性,文章还讨论了CMOS静态数字集成电路高温电学特性的分析方法。本文提出了的CMOS数字集成电路的高温学特性模型和实验结果相接近。 相似文献
1000.
As the minimum feature size of interconnect lines decreases below 0.5 urn, the need to control the line microstructure becomes
increasingly important. The alloy content, deposition process, fabrication method, and thermal history all determine the microstructure
of an interconnect, which, in turn, affects its performance and reliability. The motivation for this work was to characterize
the microstructure of various sputtered Al-Pd alloys (Al-0.3wt.%Pd, Al-2Cu-0.3Pd, and Al-0.3Nb-0.3Pd) vs sputtered Al-Cu control
samples (Al-0.5Cu and Al-2Cu) and to assess the role of grain size, mechanical stress, and crystallographic texture on the
electromigration behavior of submicrometer wide lines. The grain size, mechanical stress, and texture of blanket films were
measured as a function of annealing. The as-deposited film stress was tensile and followed a similar stress history on heating
for all of the films; on cooling, however, significant differences were observed between the Al-Pd and Al-Cu films in the
shape of their stress-temperature-curves. A strong (111) crystallographic texture was typically found for Al-Cu films deposited
on SiO2. A stronger (111) texture resulted when Al-Cu was deposited on 25 nm titanium. Al-0.3Pd films, however, exhibited either
a weak (111) or (220) texture when deposited on SiO2, which reverted to a strong (111) texture when deposited on 25 nm titanium. The electromigration lifetimes of passivated,
≈0.7 μm wide lines at 250°C and 2.5 × 106 A/cm2 for both single and multi-level samples (separated with W studs) are reported. The electromigration behavior of Al-0.3Pd
was found to be less dependent on film microstructure than on the annealing atmosphere used, i.e. forming gas (90% N2-10%H2) annealed Al-0.3Pd films were superior to all of the alloys investigated, while annealing in only N2 resulted in poor lifetimes. 相似文献