全文获取类型
收费全文 | 65812篇 |
免费 | 4770篇 |
国内免费 | 3431篇 |
专业分类
电工技术 | 1203篇 |
技术理论 | 5篇 |
综合类 | 5008篇 |
化学工业 | 3277篇 |
金属工艺 | 17950篇 |
机械仪表 | 3229篇 |
建筑科学 | 15705篇 |
矿业工程 | 1211篇 |
能源动力 | 1016篇 |
轻工业 | 1110篇 |
水利工程 | 806篇 |
石油天然气 | 2010篇 |
武器工业 | 371篇 |
无线电 | 406篇 |
一般工业技术 | 6517篇 |
冶金工业 | 13344篇 |
原子能技术 | 414篇 |
自动化技术 | 431篇 |
出版年
2024年 | 96篇 |
2023年 | 619篇 |
2022年 | 1630篇 |
2021年 | 1851篇 |
2020年 | 1959篇 |
2019年 | 1430篇 |
2018年 | 1184篇 |
2017年 | 1918篇 |
2016年 | 2032篇 |
2015年 | 2357篇 |
2014年 | 4145篇 |
2013年 | 3607篇 |
2012年 | 4812篇 |
2011年 | 5599篇 |
2010年 | 4232篇 |
2009年 | 4345篇 |
2008年 | 3478篇 |
2007年 | 4482篇 |
2006年 | 4021篇 |
2005年 | 3342篇 |
2004年 | 2792篇 |
2003年 | 2397篇 |
2002年 | 2048篇 |
2001年 | 1716篇 |
2000年 | 1479篇 |
1999年 | 1207篇 |
1998年 | 955篇 |
1997年 | 916篇 |
1996年 | 781篇 |
1995年 | 572篇 |
1994年 | 505篇 |
1993年 | 343篇 |
1992年 | 298篇 |
1991年 | 206篇 |
1990年 | 171篇 |
1989年 | 149篇 |
1988年 | 101篇 |
1987年 | 46篇 |
1986年 | 28篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 39篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1959年 | 10篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
《International Journal of Hydrogen Energy》2021,46(70):34970-34982
Alloy hardened steels offer excellent combination of mechanical properties, hardenability and corrosion resistance. 34CrMo4 is a medium carbon, low alloy steel widely used due to a good combination of high-strength, toughness and wear resistance. However, this steel experiences hydrogen embrittlement (HE), a complex phenomenon depending on the composition and microstructure. This work estimates de loss of the mechanical properties caused by hydrogen in electrochemically H-charged specimens in absence of mechanical stress but also, at low strain rate and constant load. H-charging for 2 and 6 h induce YS losses of about 40% and 71% and UTS losses of 39% and 59%, respectively. The synergistic effect of the stress and the H-charging process leads to a higher loss, 91%, and a faster brittle fracture even though hydrogen content is similar to those firstly H-charged and then tested in air. 相似文献
22.
摘要:为了研究300M超高强钢在中性盐雾环境中的腐蚀行为及腐蚀机制,采用失重法,宏观、微观腐蚀形貌分析,三维表面轮廓分析及电化学分析的研究方法,来表征腐蚀实验现象并进行分析。结果表明:300M超高强钢在中性盐雾环境中的腐蚀产物为FeOOH、Fe2O3、Fe(OH)3和Fe3O4;腐蚀速率随着腐蚀时间逐渐降低,腐蚀后期(72h)腐蚀速率降低50%;腐蚀初期以点蚀为主,点蚀坑通过横向扩展,逐渐发展为后期的均匀腐蚀,腐蚀表面形貌呈沟壑状;外腐蚀层对基体的保护能力很弱,Cr元素在锈层靠近基体的一侧偏聚使内腐蚀层具有一定的抗腐蚀性。 相似文献
23.
There are many potential causes of corrosion in animal buildings. Animals exhale large quantities of moisture into the air creating high relative humidity in the building if the moisture is not properly vented. High humidity increases the potential for condensation. In addition, ammonia may be found in large quantities in animal buildings. Ammonia is released from manure and urine. In addition, ammonium chloride is used as a nitrogen source in fertilisers. In this study, the atmospheric corrosion of hot-dip-galvanised steel and zinc alloy-coated steel such as zinc–aluminium and zinc–aluminium–magnesium has been studied in atmospheres containing different levels of ammonia. Investigations have also been conducted at different levels of ammonium chloride. The results are discussed in view of the mechanisms of corrosion of zinc and zinc alloy-coated steel in ammonia and ammonium chloride-containing environments. 相似文献
24.
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
25.
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
26.
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
27.
28.
29.
30.