全文获取类型
收费全文 | 47983篇 |
免费 | 6201篇 |
国内免费 | 4251篇 |
专业分类
电工技术 | 5345篇 |
技术理论 | 1篇 |
综合类 | 5624篇 |
化学工业 | 3652篇 |
金属工艺 | 3212篇 |
机械仪表 | 3421篇 |
建筑科学 | 3169篇 |
矿业工程 | 1793篇 |
能源动力 | 1885篇 |
轻工业 | 1450篇 |
水利工程 | 1528篇 |
石油天然气 | 5513篇 |
武器工业 | 760篇 |
无线电 | 6491篇 |
一般工业技术 | 5819篇 |
冶金工业 | 1564篇 |
原子能技术 | 808篇 |
自动化技术 | 6400篇 |
出版年
2024年 | 261篇 |
2023年 | 793篇 |
2022年 | 1433篇 |
2021年 | 1627篇 |
2020年 | 1727篇 |
2019年 | 1496篇 |
2018年 | 1396篇 |
2017年 | 1856篇 |
2016年 | 1947篇 |
2015年 | 2028篇 |
2014年 | 2793篇 |
2013年 | 2849篇 |
2012年 | 3527篇 |
2011年 | 3736篇 |
2010年 | 2789篇 |
2009年 | 2814篇 |
2008年 | 2590篇 |
2007年 | 3192篇 |
2006年 | 3012篇 |
2005年 | 2493篇 |
2004年 | 2136篇 |
2003年 | 1909篇 |
2002年 | 1549篇 |
2001年 | 1293篇 |
2000年 | 1262篇 |
1999年 | 1059篇 |
1998年 | 819篇 |
1997年 | 734篇 |
1996年 | 635篇 |
1995年 | 548篇 |
1994年 | 464篇 |
1993年 | 312篇 |
1992年 | 260篇 |
1991年 | 211篇 |
1990年 | 207篇 |
1989年 | 207篇 |
1988年 | 135篇 |
1987年 | 61篇 |
1986年 | 48篇 |
1985年 | 38篇 |
1984年 | 36篇 |
1983年 | 19篇 |
1982年 | 27篇 |
1981年 | 17篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1959年 | 11篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
本文采用粘滞流模型试验对青海桥头电厂河子沟灰场拦洪坝设计方案进行了论证,分析了多种防渗条件下的渗流场特点,提出了满足工程运作的既经济又合理的建议。 相似文献
82.
FLOW OF NEWTONIAN FLUIDS THROUGH SINUSOID ALLY CONSTRICTED TUBES. NUMERICAL AND EXPERIMENTAL RESULTS
J. A. Deiber Mb. Peirotti R. A. Bortolozzi R. J. Durelli 《Chemical Engineering Communications》1992,117(1):241-262
Numerical and experimental predictions of pressure drops in the flow of Newtonian fluids through sinusoidally constricted tubes (SCT) are carried out. The numerical evaluations analyzed in this work are obtained from the following methods: Geometric Iteration (GJM), Geometric Iteration with First and Second Upwinds (GIM1, GIM2), Successive Over Relaxation by Line (SORBLM), Global Galerkin Spectral Method (GGSM), Collocation (CM) and Dufort-Frankel (DFM). The GIM1, GIM2 and SORBLM are applied to SCT and explained in this work. The other methods have been previously reported in the literature with the same purpose. Experiments are accomplished for constrictions of approximately 40,60 and 80% of the average tube diameter and results compare well with numerical predictions of the steady flow. It is concluded that special attention should be given to evaluations of the friction factor ƒ for Reynolds numbers Re between the onsets of flow separation and turbulence due to flow instability. Finally, the SCT as a model for porous media (PM) is discussed. 相似文献
83.
针对一类特殊而不能直接对其观察的管道(如动物的血管),为了准确了解其内部特征和形态,借助计算机给出了一种用腐蚀算法来重建管道原形的方法。这种方法简单易行,而且精确度高。 相似文献
84.
基于物质平衡方程、产能方程和递减方程的结合,提出了定容气田开发规划的概算法.该法可用于预测地层压力、井底流动压力、井口流动压力和稳产年限.实际应用表明,本文提供的方法是实用有效的. 相似文献
85.
Satoshi Takeuchi Ryo Sugihara 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1998,410(3):104-508
The longitudinal electric field of single and double Gaussian laser beams are used to accelerate electrons. The longitudinal field of the single beam is concentrated on the axis and is favourable for acceleration. A set of two beams is considered. Beams run parallel, collinearly, overlap partially and have a phase difference iπ in between. As a result, the transverse components of fields cancel each other while the longitudinal components are double-fold. In both schemes, the electrons are accelerated in lengths of the Rayleigh range, which is common to the plasma-based accelerators. 相似文献
86.
87.
高频脉冲微束等离子电弧温度场的测试及分析 总被引:1,自引:1,他引:0
本文首次采用单波长激光干涉技术,对恒定直流和高频脉冲电流微束等离子电弧温度场进行了测试,并做了分析比较。以电弧温度分布为基础分析了高频脉冲电流微束等离子电弧收缩、稳定的原因。 相似文献
88.
Scale and sludge from Bulalo geothermal field, Philippines, have been characterized by whole rock analysis, radioactivity counting, size analysis, light microscopy, scanning electron microscopy, and X-ray diffraction. Their leachability was assessed by regulatory leaching procedures and by sequential extraction. Both scale and sludge consisted mostly of oxides of Si, Al, and Fe with no radionuclides detected. The scale had 10% S content. Sulfides and silicates were important phases in both samples having size ranges from submicron to 2 mm. Geothermal soils at Bulalo have higher than normal soil levels of As, S, Cu, Cr, Zn, and Pb but regulatory leaching tests indicated that these elements are not released. However, the sequential extraction showed that As, Cu, and Zn were leachable under extreme conditions. 相似文献
89.
90.
Anionic copolymerizations of styrene (M1) with excess 1-(4-dimethyl-aminophenyl)-1-phenylethylene (M2) were conducted in benzene at 25°C for 24h, using sec-butyllithium as initiator. Narrow molecular weight distribution copolymers with M?;n = 16.1 × 103 g/mol (M?w/M?n = 1.04) and 38.2 × 103g/mol (M?w/M?n = 1.05), and 24 and 38 moles of M2 per macromolecule, respectively, were characterized by size exclusion chromatography, 1H NMR spectroscopy and DSC. The monomer reactivity ratio, r1 = 5.6, was obtained from the copolymer composition at complete consumption of M1, assuming that the rate constant k22 =0,i.e. r2 =0. The polymers exhibited Tg values of 128 and 119°C, respectively, which correspond to an estimated Tg = 217°C for the hypothetical homopolymer of M2. 相似文献