全文获取类型
收费全文 | 86076篇 |
免费 | 6609篇 |
国内免费 | 4262篇 |
专业分类
电工技术 | 1818篇 |
技术理论 | 5篇 |
综合类 | 6829篇 |
化学工业 | 4910篇 |
金属工艺 | 20810篇 |
机械仪表 | 4935篇 |
建筑科学 | 18021篇 |
矿业工程 | 1781篇 |
能源动力 | 2169篇 |
轻工业 | 1630篇 |
水利工程 | 1183篇 |
石油天然气 | 3263篇 |
武器工业 | 628篇 |
无线电 | 2383篇 |
一般工业技术 | 9242篇 |
冶金工业 | 15154篇 |
原子能技术 | 702篇 |
自动化技术 | 1484篇 |
出版年
2024年 | 138篇 |
2023年 | 805篇 |
2022年 | 2043篇 |
2021年 | 2331篇 |
2020年 | 2499篇 |
2019年 | 1866篇 |
2018年 | 1570篇 |
2017年 | 2555篇 |
2016年 | 2699篇 |
2015年 | 3038篇 |
2014年 | 5367篇 |
2013年 | 4696篇 |
2012年 | 6218篇 |
2011年 | 7158篇 |
2010年 | 5485篇 |
2009年 | 5519篇 |
2008年 | 4467篇 |
2007年 | 5861篇 |
2006年 | 5249篇 |
2005年 | 4392篇 |
2004年 | 3695篇 |
2003年 | 3227篇 |
2002年 | 2781篇 |
2001年 | 2382篇 |
2000年 | 2036篇 |
1999年 | 1677篇 |
1998年 | 1344篇 |
1997年 | 1242篇 |
1996年 | 1047篇 |
1995年 | 818篇 |
1994年 | 686篇 |
1993年 | 464篇 |
1992年 | 408篇 |
1991年 | 296篇 |
1990年 | 234篇 |
1989年 | 200篇 |
1988年 | 134篇 |
1987年 | 67篇 |
1986年 | 40篇 |
1985年 | 31篇 |
1984年 | 31篇 |
1983年 | 32篇 |
1982年 | 28篇 |
1981年 | 19篇 |
1980年 | 39篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1959年 | 15篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
31.
Kiran Kousar Thomas Ljungdahl Alexander Wetzel Michael Dowhyj Hans Oskarsson Alex S. Walton Monika S. Walczak Robert Lindsay 《Journal of surfactants and detergents》2020,23(1):225-234
An optimized one-pot recipe has been developed to synthesize a surfactant molecule, referred to as OMID, consisting of an imidazoline head group and aliphatic tail, which is an exemplar corrosion inhibitor for carbon steel in acidic solutions. As evidenced by gas chromatography, 1H and 13C nuclear magnetic resonance, and Fourier-transform infrared data, a high-purity product was achieved without the use of either a solvent or catalyst. Critical micelle concentration values and corrosion inhibition efficiencies ( η %) were determined in aqueous solutions of hydrochloric acid and sulfuric acid using surface tensiometry and linear polarization resistance measurements, respectively. Hydrolysis of the imidazoline head group as a function of pH (0–11) was explored with ultraviolet–visible absorption spectroscopy. In addition, N 1s and C 1s X-ray photoelectron spectroscopy data were acquired from both surface-adsorbed OMID and a multilayer of the imidazoline head group of OMID. These latter data are highly relevant to those attempting to understand OMID inhibition chemistry. 相似文献
32.
Abrasive water jet technology can be used for micro-milling using recently developed miniaturized nozzles. Abrasive water jet (AWJ) machining is often used with both the nozzle tip and workpiece submerged in water to reduce noise and contain debris. This paper compares the performance of submerged and unsubmerged abrasive water jet micro-milling of channels in 316L stainless steel and 6061-T6 aluminum at various nozzle angles and standoff distances. The effect of submergence on the diameter and effective footprint of AWJ erosion footprints was measured and compared. It was found that the centerline erosion rate decreased with channel depth due to the spreading of the jet as the effective standoff distance increased, and because of the growing effect of stagnation as the channel became deeper. The erosive jet spread over a larger effective footprint in air than in water, since particles on the jet periphery were slowed much more quickly in water due to increased drag. As a result, the width of a channel machined in air was wider than that in water. Moreover, it was observed that the instantaneous erosion rate decreased with channel depth, and that this decrease was a function only of the channel cross-sectional geometry, being independent of the type of metal, the jet angle, the standoff distance, and regardless of whether the jet was submerged or in air, in either the forward or backward directions. It is shown that submerged AWJM results in narrower features than those produced while machining in air, without a decrease in centerline etch rate. 相似文献
33.
In this article, two novel kinds of focusing elements as reflectors are analyzed and compared. One is the grooved Fresnel zone plate reflector with continuous phase‐correcting. The other called subzone paraboloid reflector, has the profile that consists of a series of paraboloids. Their diffraction efficiencies and bandwidths are described. The two elements still preserve the advantages of Fresnel zone plates, namely, low profile, high efficiency, and simple fabrication. Two dual‐reflector antennas using the proposed focusing elements as the main reflectors are simulated and the results show that these antennas have good radiation performances. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:101–108, 2015. 相似文献
34.
为研究不同退火温度下高强IF钢的组织性能及织构的变化规律,采用温箱式电阻炉加热模拟罩式退火工艺,研究了不同退火温度下高强IF钢210P1冷轧板力学性能;对不同退火温度钢板的r90进行了统计并对其进行显微组织观察;采用X射线衍射仪及热场发射扫描电镜对不同退火温度的罩式退火成品板进行了织构分析。结果表明,在高强IF钢210P1冷轧板的罩式退火过程中,提高退火温度将使晶粒明显长大。随着退火温度的升高,屈服强度及抗拉强度下降,伸长率升高,n值略有上升,板材横向r值增加较明显,有利织构{111}取向密度增加,不利织构{100}取向密度降低。 相似文献
35.
36.
为了在腔磁力系统中实现可控的磁子诱导透明、磁力诱导透明以及快慢光传播,建立了一个混合腔磁力系统.该系统由一个含有YIG球的微波腔和在z方向对球施加一个均匀的偏置磁场组成,并用强泵浦场驱动磁子和弱探测场驱动微波腔.研究表明,通过调节腔与磁子之间的相互作用强度和微波腔与磁子的耗散比,可以增加磁子诱导透明(MIT)、磁力诱导透明(MMIT)的效果和提高快慢光传播的速度.该研究结果可为磁力诱导放大、量子光学操纵和量子信息存储以及灵敏光开关的研究提供参考. 相似文献
37.
38.
39.
40.
通过对42CrMo4风机主轴结构尺寸、性能要求、材质特点等方面进行分析,对原有锻后热处理工艺进行优化,制定出既能达到锻后热处理效果又经济节能的工艺参数。 相似文献