全文获取类型
收费全文 | 4289篇 |
免费 | 130篇 |
国内免费 | 106篇 |
专业分类
电工技术 | 144篇 |
综合类 | 238篇 |
化学工业 | 1489篇 |
金属工艺 | 115篇 |
机械仪表 | 259篇 |
建筑科学 | 362篇 |
矿业工程 | 84篇 |
能源动力 | 171篇 |
轻工业 | 170篇 |
水利工程 | 56篇 |
石油天然气 | 84篇 |
武器工业 | 11篇 |
无线电 | 247篇 |
一般工业技术 | 275篇 |
冶金工业 | 100篇 |
原子能技术 | 48篇 |
自动化技术 | 672篇 |
出版年
2023年 | 22篇 |
2022年 | 27篇 |
2021年 | 25篇 |
2020年 | 31篇 |
2019年 | 32篇 |
2018年 | 33篇 |
2017年 | 26篇 |
2016年 | 49篇 |
2015年 | 49篇 |
2014年 | 95篇 |
2013年 | 100篇 |
2012年 | 117篇 |
2011年 | 155篇 |
2010年 | 107篇 |
2009年 | 127篇 |
2008年 | 121篇 |
2007年 | 167篇 |
2006年 | 142篇 |
2005年 | 143篇 |
2004年 | 125篇 |
2003年 | 129篇 |
2002年 | 114篇 |
2001年 | 75篇 |
2000年 | 92篇 |
1999年 | 76篇 |
1998年 | 83篇 |
1997年 | 66篇 |
1996年 | 62篇 |
1995年 | 108篇 |
1994年 | 74篇 |
1993年 | 25篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1986年 | 9篇 |
1985年 | 161篇 |
1984年 | 291篇 |
1983年 | 346篇 |
1982年 | 264篇 |
1981年 | 347篇 |
1980年 | 155篇 |
1979年 | 67篇 |
1978年 | 81篇 |
1977年 | 38篇 |
1976年 | 19篇 |
1975年 | 34篇 |
1974年 | 15篇 |
1973年 | 7篇 |
排序方式: 共有4525条查询结果,搜索用时 14 毫秒
31.
GAOHui LIYan YANGLi-ping DENGHong 《半导体光子学与技术》2005,11(2):85-88,106
Hexagonal microtube ZnO was firstly grown on single crystal p-Si (111) substrates by hydrothermal method, and fabricated Ag/n-ZnO and Au/n-ZnO Schottky junction. Schottky effective barrier heights were calculated by I-V measurement. It is confirmed that the presence of a large amount of surface states related possibly to lattice imperfections existed near the surface leads to the pinning of the surface Fermi level at 0.35 eV below the conduction-band edge. Then the fabricated Schottky barrier junctions are evaluated for their use as UV photodetectors. 相似文献
32.
In this note the stability of a second-order quasi-polynomial with a single delay is studied. Although there is a vast literature on this problem, most available solutions are limited to some particular cases. Moreover, some published results on this subject appear to contain imprecise, or even wrong, conditions. The purpose of this note is to show that by accurate application of known theories, a complete explicit characterization of stability regions can be derived in a most general case. As a byproduct of the proposed analysis, we show that in the high-order case the quasi-polynomial is delay-independent unstable whenever its delay-free version has an odd number of unstable roots (or, equivalently, a negative static gain). 相似文献
33.
Thermodynamic principles, involving mainly: (1) minimum reversible work of separation and (2) second-law analysis that accounts for irreversibility, are used to synthesize separation trains. These principles lead to a development and classification into two groups of many of the heuristics appearing in the literature. An efficient algorithm based on reversible thermodynamics leads to optimal structures for simple acyclic trains. Complex structures are efficiently synthesized by algorithms using reversible thermodynamics and second-law analysis. The procedures presented are depth-first algorithms. The optimal structures developed are shown to be strongly influenced by feed and product compositions. 相似文献
34.
Krystal M. Lee 《Energy》1985,10(7):785-791
Low temperature corrosion from flue gases is a common problem in energy recovery systems. We present a simple computation procedure to estimate the dewpoint of combustion gases, which is the limiting design temperature to prevent corrosion. If the composition of fuel oil and the percentage of CO2 or O2 in the flue gases are known, the air ratio, percentage of H2O, p.p.m. of SO3 in the flue gas, and the dewpoint can be estimated with an error of 1.9%. The results indicate that the dewpoint is high because the combustion conditions are not appropriately adjusted, even if low sulfur fuel oil is used. We conclude that both the fuel quality and the combustion conditions are controlling variables in the design and operation of energy recovery systems. 相似文献
35.
本文测算了自蔓延高温合成TiAl基合金粉末的爆炸烧结特性常数值:γ=1.44,lgβ=25.25,并为试验证实,这为获取大尺寸TiAl基合金提供了理论依据。 相似文献
36.
感应电机和变压器激磁电路的参数是非线性的.为准确求取它们的特性曲线,需要的计算量很大.应用本文引入的方法可以避免大的计算量又可得到准确的特性曲线. 相似文献
37.
覃德泽 《网络安全技术与应用》2012,(4):60-62
本文简述了对等网络的概念及分类,分析了结构化对等网络特性、存在问题和关键技术,指出结构化对等网络的发展前景。 相似文献
38.
Michel Renou Bernard Lalanne-Cassou Didier Michelot Ginette Gordon Jean-Christophe Doré 《Journal of chemical ecology》1988,14(4):1187-1215
Female-emitted pheromones and sex attractants of Noctuidae were investigated using a specific computer procedure to analyze data collected from the literature. Correspondence analysis was used to survey the structure-activity relationships of sex pheromones in seven subfamilies. Structural, stereochemical, and functional features of active molecules were related to taxonomy. This multidimensional analysis revealed that the prevalent chemical frame of noctuid moth pheromones was a monounsaturated acetate withZ stereochemistry and a double bond on the fifth carbon closest to the nonfunctional branch of the molecule. Possible phylogenetic relationships within Noctuidae and between Noctuidae and other families are discussed in light of the sex pheromone biochemistry. Female sex pheromones appeared to be an additional character to be considered in the classification of noctuid moths. 相似文献
39.
Owing to its well-known high complexing power toward Al3+ ion, fluoride ion is able to increase the solubility of alumina in alkali chloride melts. To determine the extent of this effect, the formation of aluminium(III) fluoro-complexes was studied potentiometrically in LiCl-KCl eutectic at 470°. But the sodium fluoride addition appeared to produce not only the complexation effect but also a mineralization effect on alumina. So, the thermodynamical stability of alumina formed in this melt by precipitation from aluminium chloride with carbonate ion (oxide anion donor) depends on the fluoride ion concentration. These two effects explain the solubility variation of alumina in the LiCl-KCl eutectic + NaF mixtures. A pF? - pO2? diagram, which represents the stability area of the various aluminium (III) species is established, and leads to some conclusions concerning the electrowinning of aluminium from molten chloride melts.The cumulative formation constants of the aluminium(lII) fluoro-complexes (AlF3?ii) have been obtained, whose values are the following: 2.5 ± 0.4, 4.7 ± 0.6, 5.7 ± 0.5, 7.5 ± 0.4, 8.0 ± 0.5, 9.0 ± 0.6, respectively for i = 1, 2, 3, 4, 5 and 6. It has been shown that oxyfluoride species such as AlOF1?ji does not exist. The solubility products of gamma and alpha-alumina have been determined and are equal to 10?42.9 and 10?44.0 respectively (all the constants are given in the molality scale). They differ widely from the solubility product of the alumina obtained in the absence of fluoride ion, ie 10?27.4. 相似文献
40.