全文获取类型
收费全文 | 154730篇 |
免费 | 14860篇 |
国内免费 | 9140篇 |
专业分类
电工技术 | 8098篇 |
技术理论 | 11篇 |
综合类 | 12482篇 |
化学工业 | 18241篇 |
金属工艺 | 25412篇 |
机械仪表 | 7903篇 |
建筑科学 | 28395篇 |
矿业工程 | 6157篇 |
能源动力 | 2881篇 |
轻工业 | 8802篇 |
水利工程 | 3838篇 |
石油天然气 | 7181篇 |
武器工业 | 1291篇 |
无线电 | 7544篇 |
一般工业技术 | 16110篇 |
冶金工业 | 18565篇 |
原子能技术 | 1355篇 |
自动化技术 | 4464篇 |
出版年
2024年 | 441篇 |
2023年 | 1924篇 |
2022年 | 4003篇 |
2021年 | 4931篇 |
2020年 | 5143篇 |
2019年 | 4240篇 |
2018年 | 3970篇 |
2017年 | 5245篇 |
2016年 | 5636篇 |
2015年 | 5996篇 |
2014年 | 9767篇 |
2013年 | 8981篇 |
2012年 | 11474篇 |
2011年 | 12250篇 |
2010年 | 8988篇 |
2009年 | 9313篇 |
2008年 | 8042篇 |
2007年 | 10259篇 |
2006年 | 9373篇 |
2005年 | 7896篇 |
2004年 | 6648篇 |
2003年 | 5828篇 |
2002年 | 5029篇 |
2001年 | 4384篇 |
2000年 | 3711篇 |
1999年 | 3072篇 |
1998年 | 2348篇 |
1997年 | 1973篇 |
1996年 | 1743篇 |
1995年 | 1335篇 |
1994年 | 1121篇 |
1993年 | 807篇 |
1992年 | 668篇 |
1991年 | 477篇 |
1990年 | 388篇 |
1989年 | 347篇 |
1988年 | 237篇 |
1987年 | 157篇 |
1986年 | 80篇 |
1985年 | 92篇 |
1984年 | 62篇 |
1983年 | 46篇 |
1982年 | 55篇 |
1981年 | 41篇 |
1980年 | 65篇 |
1979年 | 23篇 |
1975年 | 9篇 |
1964年 | 14篇 |
1963年 | 8篇 |
1959年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The corrosion mechanisms of T24, T92, VM12, and AISI 304 steels are studied under the influence of NaCl–KCl, NaCl–Na2SO4, and KCl–K2SO4 salt mixtures in a dry air atmosphere at 650°C for 15 days. NaCl–KCl was the most aggressive deposit and AISI 304 stainless steel exhibited the highest corrosion resistance. There was no relation between the Cr content of the ferritic steels and their corrosion resistance in NaCl–KCl. In contrast, the resistance of high-Cr steels was better when exposed to NaCl–Na2SO4 and KCl–K2SO4. The high-Cr and the low-Cr steels were more susceptible to NaCl–Na2SO4 and to KCl–K2SO4, respectively. 相似文献
22.
23.
24.
Because of heat amount is different from peripheral to central of friction welding interface, which is leaded to vary the characterizations along that interface. Current study, respectively, focused on the effect of different friction pressure on micro-structural and mechanical properties of that friction welding joint interface. Presently, these friction pressures are 110, 130, 150 and 170 MPa while kept all other conditions constant. The effects of different friction pressure on welding interface characterization were investigated by EDX, SEM, tensile, compression, impact and hardness tests. The tensile tests carried out on the standardized test piece with diameter 6 mm and 8 mm, thus, compression tests were extracted from the positions of 0°, 45° 90° with test specimen of 4 mm diameter and 6.5 mm length at weld center. Whereas, the impact test pieces were picked up in two positions, the first one is symmetrical, which it obtained to the respect of the rotation axis and the interface, on the other hand, the second one is non-symmetrical with the axis of rotation and symmetrical to the interface, for making the notch head coincide with the center of the welded joint, The obtained results showed that with reducing of friction pressure will present lack of bonding increasing from peripheral toward the welding center, which will responsible on reducing of the mechanical properties such as tensile, compression and impact strength. 相似文献
25.
为研究钢管套筒灌浆连接轴向受拉破坏过程及破坏机理,试验中设计了16组48个钢管套筒灌浆连接试件,试件采用钢板代替圆钢管,并进行静载试验。分析了灌浆料裂缝扩展过程、荷载-相对位移曲线,并对抗剪键高距比、灌浆料厚度、侧向力等因素对破坏过程及承载力的影响进行分析。结果表明:对于不设置抗剪键的套筒灌浆连接试件,斜裂缝随机产生,裂缝分布不均匀;对于设置抗剪键的套筒灌浆连接试件,裂缝首先出现在底部抗剪键位置处,与水平方向夹角约为30°,随后在中部和上部抗剪键位置处分别出现斜裂缝。由于每个抗剪键上荷载分担并不均匀,与抗剪键接触的灌浆料逐渐达到极限压应力,达到极限状态时,承载力全部由抗剪键间的机械咬合力承担,在连接承载力中,可忽略摩擦力和胶结力作用。随着抗剪键高距比h/s增大,各试件初始剪切刚度相差不大,承载力增大,但增幅逐渐减小,建议抗剪键高距比0.06g/s>0.3,同时需要满足灌浆料灌注的施工要求。 相似文献
26.
27.
《Oil and Energy Trends》2020,45(1):56-58
Currency exchanges rates – updated monthly. Economic indicators of industrial production. Countries included: France, Germany, Italy, the United Kingdom, the United States, Canada, Japan (Total G-7), Eurozone and Total EU-28 (Total OECD). Updated monthly. Economic indicators of car registration in the United States, Canada, France, Germany, Italy, Poland, Spain, Turkey, the United Kingdom, Japan, Republic of Korea and Other OECD (Total OECD-30). Updated monthly. Monthly averages of crude steel production in thousand metric tons for the United States, Canada, Brazil, Mexico, Austria, Belgium, Czech Republic, France, Germany, Italy, Netherlands, Poland, Spain, Sweden, Turkey, the United Kingdom, Russia, Ukraine, South Africa, Iran, China, India, Japan, Republic of Korea, Taiwan and Australia. 相似文献
28.
29.
30.
Robert Bertuzzi 《岩石力学与岩土工程学报(英文版)》2019,11(3):494-510
This paper presents the results of ongoing research carried out by the author exploring methods to provide a more robust estimate of rock mass properties specifically for use in tunnel design. Data from various large-scale rock mass failures are introduced, including coal pillars. The damage-initiation,spalling-limit approach is compared to the coal pillar database. New comparisons of estimating the geological strength index(GSI) and relationships to estimate the Hoeke Brown failure criterion parameters, mb, s and a, are presented. 相似文献