全文获取类型
收费全文 | 10973篇 |
免费 | 1120篇 |
国内免费 | 723篇 |
专业分类
电工技术 | 307篇 |
技术理论 | 2篇 |
综合类 | 945篇 |
化学工业 | 611篇 |
金属工艺 | 978篇 |
机械仪表 | 1476篇 |
建筑科学 | 1064篇 |
矿业工程 | 207篇 |
能源动力 | 435篇 |
轻工业 | 143篇 |
水利工程 | 4480篇 |
石油天然气 | 319篇 |
武器工业 | 42篇 |
无线电 | 385篇 |
一般工业技术 | 864篇 |
冶金工业 | 187篇 |
原子能技术 | 42篇 |
自动化技术 | 329篇 |
出版年
2024年 | 52篇 |
2023年 | 189篇 |
2022年 | 292篇 |
2021年 | 330篇 |
2020年 | 398篇 |
2019年 | 384篇 |
2018年 | 373篇 |
2017年 | 490篇 |
2016年 | 506篇 |
2015年 | 498篇 |
2014年 | 626篇 |
2013年 | 641篇 |
2012年 | 740篇 |
2011年 | 781篇 |
2010年 | 557篇 |
2009年 | 591篇 |
2008年 | 593篇 |
2007年 | 764篇 |
2006年 | 684篇 |
2005年 | 541篇 |
2004年 | 451篇 |
2003年 | 348篇 |
2002年 | 370篇 |
2001年 | 280篇 |
2000年 | 228篇 |
1999年 | 194篇 |
1998年 | 151篇 |
1997年 | 138篇 |
1996年 | 139篇 |
1995年 | 75篇 |
1994年 | 62篇 |
1993年 | 72篇 |
1992年 | 65篇 |
1991年 | 41篇 |
1990年 | 32篇 |
1989年 | 35篇 |
1988年 | 33篇 |
1987年 | 18篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1980年 | 2篇 |
1979年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Chenxu Liu Shuguang Zhang Ruonan Ji Peng Wang Jin Zhang Yu Tian Yonggang Meng Yedong He 《Ceramics International》2019,45(4):4747-4755
Semiconductor particles doped Al2O3 coatings were prepared by cathode plasma electrolytic deposition in Al(NO3)3 electrolyte dispersed with SiC micro- and nano-particles (average particle sizes of 0.5–1.7?µm and 40?nm respectively). The effects of the concentrations and particle sizes of the SiC on the microstructures and tribological performances of the composite coatings were studied. In comparison with the case of dispersing with SiC microparticles, the dispersion of SiC nanoparticles in the coatings was more uniform. When the concentration of SiC nanoparticles was 5?g/L, the surface roughness of the composite coating was reduced by 63%, compared with that of the unmodified coating. Friction results demonstrated that the addition of 5?g/L SiC nanoparticles reduced the friction coefficient from 0.60 to 0.38 and decreased the wear volume under dry friction. The current density and bath voltage were measured to analyze the effects of SiC particles on the deposition process. The results showed that the SiC particles could alter the electrical behavior of the coatings during the deposition process, weaken the bombardment of the plasma, and improve the structures of the coatings. 相似文献
2.
The mechanical property of age‐hardenable Al‐alloys is governed by the state of ageing, which determines the microstructure and consequently, their corrosion behavior which is a vital aspect for a number of applications. This article presents a comparative assessment of corrosion behavior of under‐, peak‐ and over‐aged Al‐Mg‐Si alloy. Corrosion characteristics have been determined via immersion tests in 0.1 M ortho‐phosphoric acid solution and intergranular corrosion (IGC) tests. Corroded surfaces are examined by field emission scanning electron micrographs‐energy dispersive spectroscopy and 3D optical profilometer. The obtained results reveal that the corrosion rate at a specific immersion time as well as the depth of IGC increases in the order for under‐, peak‐, and over‐aged states. Irrespective of the state of ageing, corrosion loss increases linearly but the rate of corrosion decreases rapidly with increasing immersion time. The dominant mode of corrosion in under‐aged alloy is identified as localized pitting, while peak‐aged is highly susceptible to IGC in contrast extensive pitting corrosion is observed for over‐aged alloy. The observed differences in corrosion behavior are explained considering characteristics of precipitates. Formation of β (Mg2Si) in case of over‐aged alloy and presence of inclusions like AlFeMnSi particles are found to accelerate pitting corrosion. 相似文献
3.
4.
通过物理模型试验,研究了有植被的河道水流紊动特性.试验结果表明,在复式断面河道滩地种植柔性植被后,滩地糙率增大,水流紊动更为剧烈,河道水流紊动强度峰值由原先的滩槽交界区转移到滩地区.滩地的水流紊动强度沿程递减;滩槽交界区的水流紊动强度沿程不断增大;主槽的水流紊动强度主要与床面糙率有关,滩地植被影响了滩地水流的归槽时间,使主槽水流流速沿程增大. 相似文献
5.
采用超高真空电子束蒸发法制备了新型高 K栅介质-非晶 ZrO2薄膜. X射线光电子能谱 (XPS) 中 Zr3d5/2 和 Zr3d3/2 对应的结合能分别为 182.1eV和 184.3eV, Zr元素的主要存在形式为 Zr4+,说明薄膜由完全氧化的 ZrO2组成 ,并且纵向分布均一.扩展电阻法( SRP)显示 ZrO2薄膜的 电阻率在 108Ω@ cm以上,通过高分辨率透射电镜( HR- XTEM)可以观察 ZrO2/Si界面陡直,没有 界面反应产物 ,证明 600℃快速退火后 ZrO2薄膜是非晶结构.原子力显微镜( AFM)表征了薄膜的 表面粗糙度,所有样品表面都很平整,其中 600℃快速退火样品 (RTA)的 RMS为 0.480nm. 相似文献
6.
7.
新安江流域安徽省地区水环境状况分析 总被引:2,自引:0,他引:2
统计分析流域内点源污染、面源污染产生量与污染物入河量的调查监测数据,结果表明:安徽省辖新安江流域点源入河系数约为面源入河系数2~3倍,点源污染是流域内主要污染来源,但面源污染的作用不容忽视,尤其是总磷,有近2/3来自面源,相对省辖淮河、长江两流域来说,面源污染贡献率明显增大。指出流域污染防治必须综合考虑点、面源污染两个方面;在点源污染不太严重的情况下,对面源污染的治理必须引起足够的重视,才能取得实效。 相似文献
8.
9.
10.
The planimetric shifts in channel location of large alluvial rivers are a critical component in the creation of diverse structures and functions in riverine habitats. Engineered management schemes must also compensate for this type of channel change to protect resources and maintain navigation channels. The stability of the Lower Mississippi River channel was assessed through an analysis of historical records of channel position produced and archived by the United States Army Corps of Engineers. Channel location was recorded for the years 1765, 1820, 1881, 1915, 1930, 1937, 1960 and 1970. Channel stability was measured by two introduced metrics on a cell‐by‐cell basis: (1) the standard deviation of Euclidean distance to a channel cell for the entire period of record, and (2) the rate of Euclidean distance change between years in the period of record. At a coarse spatial scale, channel instability increased in the downstream direction. The variability of channel stability also increased in the downstream direction. Analysis of this variability identified alternating areas of high and low stability occurring with greater frequency as distance downstream increased. These findings are validated by past studies of channel stability along the Lower Mississippi River. As a result, the proposed metrics provide a consistent, quantitative, efficient and cost‐effective means of identifying areas of channel instability at several spatial scales. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献