全文获取类型
收费全文 | 50901篇 |
免费 | 2720篇 |
国内免费 | 1628篇 |
专业分类
电工技术 | 1338篇 |
技术理论 | 1篇 |
综合类 | 2914篇 |
化学工业 | 7968篇 |
金属工艺 | 5797篇 |
机械仪表 | 2217篇 |
建筑科学 | 1672篇 |
矿业工程 | 706篇 |
能源动力 | 1309篇 |
轻工业 | 2844篇 |
水利工程 | 263篇 |
石油天然气 | 1047篇 |
武器工业 | 408篇 |
无线电 | 4474篇 |
一般工业技术 | 10110篇 |
冶金工业 | 1610篇 |
原子能技术 | 578篇 |
自动化技术 | 9993篇 |
出版年
2024年 | 43篇 |
2023年 | 526篇 |
2022年 | 743篇 |
2021年 | 1054篇 |
2020年 | 813篇 |
2019年 | 939篇 |
2018年 | 801篇 |
2017年 | 1143篇 |
2016年 | 1548篇 |
2015年 | 2188篇 |
2014年 | 2388篇 |
2013年 | 2351篇 |
2012年 | 2713篇 |
2011年 | 3807篇 |
2010年 | 2945篇 |
2009年 | 3129篇 |
2008年 | 2800篇 |
2007年 | 2702篇 |
2006年 | 2106篇 |
2005年 | 1884篇 |
2004年 | 2428篇 |
2003年 | 2100篇 |
2002年 | 2613篇 |
2001年 | 1818篇 |
2000年 | 1587篇 |
1999年 | 1344篇 |
1998年 | 859篇 |
1997年 | 891篇 |
1996年 | 1726篇 |
1995年 | 983篇 |
1994年 | 734篇 |
1993年 | 235篇 |
1992年 | 198篇 |
1991年 | 208篇 |
1990年 | 188篇 |
1989年 | 104篇 |
1988年 | 84篇 |
1987年 | 56篇 |
1986年 | 82篇 |
1985年 | 88篇 |
1984年 | 60篇 |
1983年 | 41篇 |
1982年 | 48篇 |
1981年 | 41篇 |
1980年 | 20篇 |
1979年 | 22篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1974年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Hydrogen entry and permeation into iron were measured by an electrochemical method during atmospheric corrosion reaction. The hydrogen permeation was enhanced on passive films because the hydrogen adsorption increased by the hydrogen evolution mechanism which is different from that on a bear iron surface. The permeation rate during a wet and dry corrosion cycle showed a maximum in the drying process depending upon the surface pH and the corrosion potential. The pollutant such as Na2SO3 which decreases the pH and the corrosion potential causes an increase in the permeation rate. The mechanism of the change in the permeation rate during the wet and dry cycles is explained by the polarization diagram of the electrode covered by thin water layer. 相似文献
992.
1Cr18Mn14N不锈钢在HCl溶液中的空蚀行为 总被引:1,自引:1,他引:1
利用磁致伸缩空蚀实验机研究了1Cr18Mn14N不锈钢在HCl溶液中的空蚀行为,利用扫描电镜(SEM)跟踪观察了试样表面的空蚀形貌,测量了静态和空蚀条件下的极化曲线和电化学阻抗谱(EIS),分析了腐蚀和氢对空蚀损伤的影响,结果表明:在0.1mol/LHCl溶液中,加工硬化能力高的1Cr18Mn14N不锈钢的抗空蚀性能优于水轮机常规用材0Cr13Ni5Mo;当盐酸浓度增大为0.5mol/L时,阳极溶解和氢的共同作用促进1Cr18Mn14N不锈钢表面裂纹的形核和失稳扩展,裂纹扩展、连接引起材料大量脱落,使1Cr18Mn14N不锈钢的抗空蚀性能大大劣化,反而不如0Cr13Ni5Mo不锈钢. 相似文献
993.
Naphthenic acid corrosion (NAC) and erosion-corrosion (NAEC) behavior of Mo-bearing (0-7.0 wt.%) stainless steels have been investigated in laboratory to evaluate the essential role of Mo on their NAC and NAEC resistance. The NAC and NAEC resistance of a high-velocity-oxygen-fuel (HVOF) thermal sprayed Mo-bearing stainless-steel coating was also investigated in both laboratory and an oil refinery. It was found that increasing the Mo content remarkably enhanced the NAC and NAEC resistance of stainless steels. The Mo-rich areas or phases in the steels played an importance role in resisting the NAEC. The HVOF coating showed excellent NAC and NAEC resistance in laboratory tests. The 700-day field test in an oil refinery revealed that the coating can effectively prevent the carbon-steel substrate from erosion-corrosion during long-term exposure in oil-refining environment. The corresponding NAC and NAEC mechanisms of the stainless steels and the beneficial role of Mo were discussed by taking account of inherent susceptibility of metal elements to corrosion, possible effects of Mo on surface films, and Mo-induced change in microstructure and microhardness. 相似文献
994.
Jeong-Seb Han 《Corrosion Science》2004,46(4):787-793
The application of an infrared camera for detecting corrosion under organic coatings was studied. The ruptured blistering area, blister and filiform corrosion can be monitored easily by infrared thermography. When the corroded specimen is heated, the temperature at the surface over the corroded area changed differently according to the type of corrosion.The extent of increase in temperature was in the following sequence: ruptured blister > filiform filament > intact part > blister.From the analysis of temperature distribution at the surface of specimen, the location, shape and size of the corroded area can be estimated. 相似文献
995.
996.
The deformation behavior of AZ31B magnesium alloy as extruded under hot compression conditions was characterized in the temperature range of 200 - 400 ℃ and strain rate range of 0. 001 - 1 s^-1. The processing maps were obtained at different strains. The results show that the map exhibits flow instabilities as two domains. The domain at beyond 300 ℃ and strain rate of 1 s^-1 appears with a peak efficiency of power dissipation about 56% occurring. This domain is expected to happen in a hot process, such as hot rolling, hot extrusion and hot forging. There is high efficiency of power dissipation at temperature beyond 350 ℃ and strain rate 0. 001 s^-1. Such domains suggest the occurrence of superplastic deformation. 相似文献
997.
Microstructure and mechanical properties of wrought magnesium alloy AZ31B welded by laser-TIG hybrid 总被引:5,自引:0,他引:5
The laser-TIG hybrid welding was mainly used to weld the wrought magnesium alloy AZ31B. The tech-nical characteristics of laser-TIG hybrid welding process was investigated and the interactional mechanism between laser and arc was discussed, at the same time the microstructure and mechanical properties of the wrought magnesi-um alloy AZ31B using laser-TIG hybrid welding were analyzed by optical microscope, EPMA, SEM, tensile ma-chine, hardness machine. The experimental results show that the presence of laser beam boosts up the stability of the arc during high speed welding and augments the penetration of weld; the crystal grains of magnesium alloy weld are fine without porosity and cracks in the best welding criterion and the microstructure of HAZ does not become coarse obviously. The elements profile analysis reveals that Mg content in the weld is lower than that of the base metal, but Al content is higher slightly. Under this experimental condition, the wrought magnesium alloy AZ31B joint can be achieved using laser-TIG hybrid process and the tensile strength of the joint is equivalent to that of the base metal. 相似文献
998.
C. Cagran B. Wilthan G. Pottlacher B. Roebuck M. Wickins R. A. Harding 《Intermetallics》2003,11(11-12):1327
The families of titanium aluminide intermetallic alloys have attractive high temperature mechanical properties which make them potential candidate materials for a wide range of applications, particularly in the aeronautic and automobile sectors. The development of appropriate manufacturing techniques is an essential stage in the engineering exploitation of these materials, e.g., Induction Skull Melting is one of the techniques which needs to be optimised for the casting of titanium aluminides. Research is underway to develop a computer model of this process but data are required for the key thermophysical properties. Pulse-heating techniques have been used to measure properties for the Ti–44Al–8Nb–1B system. Rectangular samples have been prepared and are resistively heated as part of a fast capacitor discharge circuit. Time-resolved measurements with sub-μs resolution of currents through the specimen were made with a Pearson probe current monitor using the induction principle. Voltages across the specimen were determined with knife-edge contacts and voltage dividers, and radiance temperatures of the sample were measured with a pyrometer. These measurements allow the calculation of specific heat and dependencies between enthalpy, electrical resistivity and temperature of the alloy up into the liquid phase. Data for thermal diffusivity have been obtained by using the Wiedeman–Franz relation. The results are compared with those obtained using DSC and the four-probe method to measure the temperature dependence of the resistivity. 相似文献
999.
1000.
ECR微波等离子体源离子渗氮 总被引:5,自引:0,他引:5
研究了一种新的低温渗氮方法--电子回旋共振微波等离子体源离子渗氮。对纯铁、45负和35CrMo钢试样在150 ̄350℃进行渗氮处理,测定了渗氮层的硬度和晶体结构,结果表明,纯铁在低于200℃的温度即可获得连续分布的表面氮化物层,35CrMo钢在低于250℃温度处理也可获得离好渗氮层。 相似文献