全文获取类型
收费全文 | 73209篇 |
免费 | 9659篇 |
国内免费 | 5082篇 |
专业分类
电工技术 | 17628篇 |
技术理论 | 6篇 |
综合类 | 5047篇 |
化学工业 | 8262篇 |
金属工艺 | 6614篇 |
机械仪表 | 5513篇 |
建筑科学 | 2944篇 |
矿业工程 | 2307篇 |
能源动力 | 3526篇 |
轻工业 | 8091篇 |
水利工程 | 1079篇 |
石油天然气 | 1671篇 |
武器工业 | 433篇 |
无线电 | 7997篇 |
一般工业技术 | 6682篇 |
冶金工业 | 4880篇 |
原子能技术 | 1594篇 |
自动化技术 | 3676篇 |
出版年
2024年 | 384篇 |
2023年 | 1326篇 |
2022年 | 2266篇 |
2021年 | 2853篇 |
2020年 | 2782篇 |
2019年 | 2609篇 |
2018年 | 2445篇 |
2017年 | 2921篇 |
2016年 | 3139篇 |
2015年 | 3177篇 |
2014年 | 4711篇 |
2013年 | 4745篇 |
2012年 | 5558篇 |
2011年 | 6063篇 |
2010年 | 4335篇 |
2009年 | 4492篇 |
2008年 | 3996篇 |
2007年 | 4946篇 |
2006年 | 4431篇 |
2005年 | 3421篇 |
2004年 | 2957篇 |
2003年 | 2431篇 |
2002年 | 2037篇 |
2001年 | 1756篇 |
2000年 | 1514篇 |
1999年 | 1227篇 |
1998年 | 945篇 |
1997年 | 874篇 |
1996年 | 718篇 |
1995年 | 584篇 |
1994年 | 477篇 |
1993年 | 370篇 |
1992年 | 294篇 |
1991年 | 219篇 |
1990年 | 185篇 |
1989年 | 172篇 |
1988年 | 97篇 |
1987年 | 71篇 |
1986年 | 50篇 |
1985年 | 48篇 |
1984年 | 56篇 |
1983年 | 29篇 |
1982年 | 65篇 |
1981年 | 79篇 |
1980年 | 32篇 |
1979年 | 18篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1959年 | 10篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
101.
如何利用循环体诸如初值、终值、步长和下标式等数学对象的诸如恒等、正负、单调性一类的数学特征,按照严格推导出来的简单规则,绕过各种复杂的数据依赖关系图及其上诸如拓扑排序或等价变换等复杂的操作,直接从事向量化处理,这是极富实用价值的研究方向.文献[2,3,5]给出的可原形/准原形算法,以及本文的可反原形与拟离散性,正是这样的捷径.它们能使相当部分的常见循环,直接向量化. 相似文献
102.
Iwao Shimizu Yuji Naito Iwao Yamaguchi Katsuyuki Kaiho Hitoshi Mizoguchi Satoru Yanabu 《Electrical Engineering in Japan》2008,164(1):52-61
Using conventional high‐temperature superconducting wire, a model superconducting fault current limiter (SFCL) is made and tested. Solenoid coil using Bi2223 silver sheath wire is so made that inductance is as small as possible and a vacuum interrupter is connected in series to it. A conventional reactor coil is connected in parallel. When the fault current flows in this equipment, superconducting wire is quenched and current is transferred into the parallel coil because of voltage drop of superconducting wire. This large current in parallel coil actuates magnetic repulsion mechanism of vacuum interrupter. Due to opening of vacuum interrupter, the current in superconducting wire is broken. By using this equipment, current flow time in superconducting wire can be easily minimized. On the other hand, the fault current is also easily limited by large reactance of parallel coil. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 52–61, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20315 相似文献
103.
提出一种配电网电容电流测量的新方法,在零序电压互感器的开口三角侧串联一个可调电感,通过注入一个变频恒流信号寻找配电网的谐振频率,改变可调电感的数值后寻找另一谐振频率,联立2个谐振方程求解电容电流,该方法消除了电压互感器漏抗对测量的影响。开发了配电网电容电流测量仪,经模拟试验和现场测试表明,该方法具有安全、快捷、准确等特点,适用于中性点不接地或经随调式消弧线圈接地配电网。 相似文献
104.
This paper presents the mass transfer results from an impinging liquid jet to a rotating disk. The mass transfer coefficients were measured using the electrochemical limiting diffusion current technique (ELDCT). Rotational Reynolds number (Rer) in the range of 3.4 × 104–1.2 × 105, jet Reynolds number (Rej) 1.7 × 104–5.3 × 104 and non-dimensional jet-to-disk spacing (H/d) 2–8 were taken into consideration as parameters. It was found that the jet impingement resulted in a substantial enhancement in the mass transfer compared to the case of the rotating disk without jet. 相似文献
105.
106.
O. Gravrand E. De Borniol S. Bisotto L. Mollard G. Destefanis 《Journal of Electronic Materials》2007,36(8):981-987
This paper aims at studying the feasibility of very long infrared wavelength (VLWIR) (12–18 μm) focal plane arrays using n-on-p planar ion-implanted technology. To explore and analyze the feasibility of such VLWIR detectors, a set of four Cd
x
Hg1−x
Te LPE layers with an 18 μ cutoff at 50 K has been processed at Defir (LETI/LIR–Sofradir joint laboratory), using both our “standard” n-on-p process and our improved low dark current process. Several 320 × 256 arrays, 30-μm pitch, have been hybridized on standard Sofradir readout circuits and tested. Small dimension test arrays characterization
is also presented. Measured photonic currents with a 20°C black body suggest an internal quantum efficiency above 50%. Typical
I(V) curves and thermal evolution of the saturation current are discussed, showing that standard photodiodes remain diffusion
limited at low biases for temperatures down to 30 K. Moreover, the dark current gain brought by the improved process is clearly
visible for temperatures higher than 40 K. Noise measurements are also discussed showing that a very large majority of detectors
appeared background limited under usual illumination and biases. In our opinion, such results demonstrate the feasibility
of high-performance complex focal plane arrays in the VLWIR range at medium term. 相似文献
107.
研究了不同温度下PTT(聚对苯二甲酸丙二醇酯)直接酯化反应动力学。建立了零级和一级反应动力学模型。用实验数据进行的检验表明,一级动力学模型更为接近该反应过程。 相似文献
108.
Hatto F. Jacobi 《国际钢铁研究》2003,74(11-12):667-678
Improvements of solidification processing in conventional or near net shape casting depend on sophisticated methods of macroscopic examination of central unsoundness and inhomogeneity of the cast material. As long as remarkable deviations referring to the quality features exist between the slab centre and the bulk material such methods should be looked after. Two semi‐macroscopic methods of segregation analysis are discussed in this paper: firstly, the potential of the emission spectral analysis combined with sectioning of a sample and secondly, the computer aided micro‐probe analysis. Both methods are restricted to small local areas. The proneness of elements and steel grades with respect to micro‐ and macrosegregation as well as distribution‐ and segregation coefficients are determined. The effect of a diffusion anneal on homogenisation of segregation is studied. Last not least the precipitation of sulphides, phosphides or carbonitrides is estimated. Ultrasonic detection of the central unsoundness of conventional slabs or thin slabs is a new approach towards a quantitative macroscopic examination. The sample size is 400 mm x 300 mm x 30 mm. To achieve a low ultrasonic noise using a 5 MHz‐transducer the samples are heat treated for grain refinement. “Dog bone porosity”, macroscopic topographical misfit between the upper and lower solidifying shells, periodical corner cracks or systematic transverse centre cracks are detected. Obviously, segregations do not reflect the ultrasonic beam. However, it can be presumed that an interrelation exists between porosity and segregation, although these might be locally apart from each other. This new ultrasonic test of the central unsoundness of continuous cast (c.c.) slabs gives valuable arguments to machine builders and maintenance people to decide on the right concepts for strand guidance, support rollers and secondary cooling. Soft reduction can be optimized and variations in casting speed counteracted by dynamic means. R&D service of this kind can help steelmakers when decisions are impending to build new casting machines or revamp old ones. 相似文献
109.
M型四能级原子与三模场相互作用系统的动力学特性 总被引:2,自引:2,他引:0
采用全量子理论,研究了M型四能级原子与三模场相互作用系统的动力学特性,通过数值计算,分析了光场失谐量、初始光子数和原子初始状态对原子布居概率和光子统计演化规律的影响. 相似文献
110.
用原子吸收次灵敏线法塞曼效应扣除背景测定土壤中Fe、Mn,实验结果表明:此方法有较好的准确度,精密度,操作简单,适合一般土壤中Fe、Mn的测定。 相似文献