全文获取类型
收费全文 | 18320篇 |
免费 | 1350篇 |
国内免费 | 1058篇 |
专业分类
电工技术 | 167篇 |
综合类 | 920篇 |
化学工业 | 2734篇 |
金属工艺 | 7930篇 |
机械仪表 | 546篇 |
建筑科学 | 193篇 |
矿业工程 | 359篇 |
能源动力 | 465篇 |
轻工业 | 304篇 |
水利工程 | 15篇 |
石油天然气 | 147篇 |
武器工业 | 164篇 |
无线电 | 393篇 |
一般工业技术 | 4424篇 |
冶金工业 | 1699篇 |
原子能技术 | 109篇 |
自动化技术 | 159篇 |
出版年
2024年 | 61篇 |
2023年 | 344篇 |
2022年 | 385篇 |
2021年 | 601篇 |
2020年 | 584篇 |
2019年 | 536篇 |
2018年 | 515篇 |
2017年 | 608篇 |
2016年 | 528篇 |
2015年 | 567篇 |
2014年 | 882篇 |
2013年 | 1174篇 |
2012年 | 1048篇 |
2011年 | 1609篇 |
2010年 | 1070篇 |
2009年 | 1158篇 |
2008年 | 999篇 |
2007年 | 1215篇 |
2006年 | 1259篇 |
2005年 | 906篇 |
2004年 | 849篇 |
2003年 | 658篇 |
2002年 | 501篇 |
2001年 | 390篇 |
2000年 | 350篇 |
1999年 | 298篇 |
1998年 | 217篇 |
1997年 | 248篇 |
1996年 | 174篇 |
1995年 | 166篇 |
1994年 | 145篇 |
1993年 | 110篇 |
1992年 | 95篇 |
1991年 | 75篇 |
1990年 | 67篇 |
1989年 | 53篇 |
1988年 | 32篇 |
1987年 | 37篇 |
1986年 | 37篇 |
1985年 | 21篇 |
1984年 | 27篇 |
1983年 | 22篇 |
1982年 | 27篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
An oscillating cup viscometer was developed to measure the absolute viscosities of molten metals. Previous experiments established the capability of the apparatus to characterize the viscosities of molten nickel-based superalloys. However, modifications to the instrument and its theoretical analysis were required for reliable measurements on molten aluminum alloys, presumably due to their lower densities and lower viscosities. The theoretical literature for the fluid flow inside an oscillating cup is reviewed, and a working equation without any correction factor is developed for the improved viscometer. Some design parameters of the viscometer that directly affect the accuracy of viscosity estimation by using the working equation are discussed. A special vertical furnace was adopted to uniformly heat a longer cylindrical sample (10 mm inner diameter and 120 mm length) with a temperature difference of less than 2°C over the sample length. The measuring procedure was also improved to get more accurate motion parameters. It is estimated that the working equation and improved instrument provide an uncertainty of less than 4%. In addition, applications and experimental data are presented for pure aluminum and three aluminum alloys: A201, A319, and A356. 相似文献
32.
Saye D. S. Abd El Rehim Soad M. Abd El Wahaab Osama M. Abdella 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(5):217-222
The electroplating of Ni-Cd alloy coatings was carried out from alkaline baths (pH 10). For comparison, electroplating of the parent metals, Ni and Cd, was performed individually under the same conditions. The cathodic current efficiency for codeposition was high and decreased with increasing current density. The codeposition process is an anomalous type of plating with Cd being the preferentially deposited metal. The Ni content in the deposits increased with increasing current density. This increase in Ni content improves the corrosion resistance and microhardness of the deposits. X-ray diffraction analysis showed that the deposits consist of a mixture of Ni, β, γ, γ1 phases. 相似文献
33.
Crack propagation tests were carried out on 2024-T3 sheet specimens to study the effects of omitting low-amplitude cycles from the gust-dominated TWIST load sequence (MiniTWIST) and the removal of small load ranges from the manoeuvre-dominated FALSTAFF load sequence (short FALSTAFF). In other tests high-amplitude loads of TWIST and MiniTWIST were truncated at different levels. The results are compared with data from similar test programmes, including crack initiation. Attention is paid to unstationary crack growth retardation and a transient retardation during initial crack growth started by an artificial crack. 相似文献
34.
35.
A bright electroless Ni-P deposition on AM50 magnesium alloy in a sulfate plating bath was proposed by using direct plating process with non-chromate pretreatment. The electroless Ni-P plating on AM50 magnesium alloy has an admirable appearance and good adhesion. The results indicate that the electroless Ni-P deposition with non-chromate pretreatment has better adhesion than that of zinc immersion coating. Anodic polarization curves indicate that the electroless Ni-P deposition obtained from the sulfate bath has similar corrosion-resistance to that obtained from basic nickel carbonate bath. The deposition process generates less pollutant by a non-chromate plating bath and is suitable for the magnesium alloys manufacture because of its low cost. The hardness of the electroless Ni-P plated AM50 is about HV 720.6 and HV 969.7 after heat treatments at 180℃ for 2 h. The wear resistance of Ni-P plated magnesium alloy specimens is about 5 to 9 times as high as that of bare magnesium alloys. 相似文献
36.
《稀有金属材料与工程》2006,23(1):32-34
叙述了用红外吸收法对钛及钛合金中氧和氢联合测定的方法,取得了测定的最佳条件。连续测定6次的相对标准偏差在10%以下,作加标回收试验的回收率为95.6%~103.9%。分析时间在3min以内,可应用于日常分析,结果满意。 相似文献
37.
Ya. Unigovski A. Eliezer E. Abramov Y. Snir E. M. Gutman 《Materials Science and Engineering: A》2003,360(1-2):132-139
Corrosion fatigue tests were carried out on extruded AZ31 (3% Al, 1% Zn, 0.3% Mn, Mg—the rest), AM50 (5% Al, 0.4% Mn, Mg—the rest) and ZK60 (5% Zn, 0.5% Zr, Mg—the rest) Mg alloys in air, NaCl-based and borate solutions. Nsol/Nair ratios (the relative fatigue life) were used for the analysis of the corrosion fatigue behavior of Mg alloys in various environments, where Nsol and Nair are the numbers of cycles to failure in the solution and in air, respectively. Extruded ZK60 alloy reveals very high fatigue and corrosion fatigue properties in comparison with other alloys. However, it has the lowest relative fatigue life (Nsol/Nair 10−3–10−2) or the highest sensitivity to the action of NaCl-based solutions in comparison with that of AM50 and AZ31 alloys (Nsol/Nair 10−2–10−1). Under the same stress, the corrosion fatigue life of extruded alloys is significantly longer than that of die-cast alloys (Nsol for extruded AM50 in NaCl is two to three times longer than that of die-cast AM50). 相似文献
38.
The influence of alloying of Pt with 20 at.% of Ni, Co and Fe has been studied in the hydrogenation of 1,3 butadiene. Iron induces the more important modifications, with both higher activity and selectivity. The results are discussed in terms of the surface segregation, the local order in surface and the electronic properties measured by photoemission of core levels. 相似文献
39.
本文研究了一种Zn-Ti合金新镀层,经盐水浸泡、中性盐雾和大气暴露试验结果试验,其耐蚀明显超过镀Zn层,并与镀Cd层相近,用缺口持久拉伸试验检验氢脆性,拉伸持续时间超过200h,达到原航空部部颁标准(HB5067-85),该镀层适用于高强度钢防护。 相似文献
40.
Oxide films formed by water oxidation at 360°C on ZrNb(1%)O(0.13%) for several durations (50-300 days) were studied by impedance spectroscopy (IS) in gaseous atmosphere. The electrical behavior of oxide layers was investigated as a function of the temperature (25-300°C) at constant oxygen partial pressure (0.3 Pa). Cole-Cole diagrams suggest a frequency-temperature equivalence. A simple electrical model has been derived from the as-deduced 14 decade master curve. Equivalent circuit includes a series association of two layers exhibiting different dielectric properties: a dense layer near the oxide-metal interface and a porous layer at the waterside. Electronic conductivity is predominant within the whole temperature range, but ionic contribution was proposed to increase for temperature higher than 170°C. During the parabolic oxidation step, the oxide thickness of the barrier layer increases but oxide growth would not be only a geometrical one. The kinetic modification to a constant oxidation rate was observed to be correlated to the increase of the dense layer thickness. Such a behavior suggests that the mechanism controlling oxidation rate is not a pure mechanism of oxygen diffusion through this layer. Finally, a qualitative model of activated electrons transport based on an hopping mechanism was proposed in order to take into account that the Arrhenius diagrams of both total conductivity and dispersion factor are characterized by a break point with two activation energy values. 相似文献