全文获取类型
收费全文 | 394542篇 |
免费 | 3478篇 |
国内免费 | 909篇 |
专业分类
电工技术 | 7021篇 |
综合类 | 278篇 |
化学工业 | 63481篇 |
金属工艺 | 20740篇 |
机械仪表 | 14795篇 |
建筑科学 | 8456篇 |
矿业工程 | 4124篇 |
能源动力 | 7626篇 |
轻工业 | 26361篇 |
水利工程 | 5187篇 |
石油天然气 | 13599篇 |
武器工业 | 33篇 |
无线电 | 39480篇 |
一般工业技术 | 90161篇 |
冶金工业 | 55254篇 |
原子能技术 | 13305篇 |
自动化技术 | 29028篇 |
出版年
2021年 | 3495篇 |
2019年 | 3524篇 |
2018年 | 6454篇 |
2017年 | 6789篇 |
2016年 | 7241篇 |
2015年 | 4063篇 |
2014年 | 7023篇 |
2013年 | 16438篇 |
2012年 | 10315篇 |
2011年 | 13306篇 |
2010年 | 10697篇 |
2009年 | 12080篇 |
2008年 | 12552篇 |
2007年 | 12521篇 |
2006年 | 10493篇 |
2005年 | 9414篇 |
2004年 | 9273篇 |
2003年 | 9011篇 |
2002年 | 8879篇 |
2001年 | 8703篇 |
2000年 | 8479篇 |
1999年 | 7748篇 |
1998年 | 13481篇 |
1997年 | 10813篇 |
1996年 | 8699篇 |
1995年 | 7203篇 |
1994年 | 6660篇 |
1993年 | 6701篇 |
1992年 | 5890篇 |
1991年 | 5946篇 |
1990年 | 6006篇 |
1989年 | 5873篇 |
1988年 | 5649篇 |
1987年 | 5335篇 |
1986年 | 5199篇 |
1985年 | 5785篇 |
1984年 | 5503篇 |
1983年 | 5284篇 |
1982年 | 5001篇 |
1981年 | 4973篇 |
1980年 | 4869篇 |
1979年 | 5085篇 |
1978年 | 5197篇 |
1977年 | 5496篇 |
1976年 | 6419篇 |
1975年 | 4747篇 |
1974年 | 4689篇 |
1973年 | 4758篇 |
1972年 | 4159篇 |
1971年 | 3832篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Up until today extreme rainfall properties are frequently applied in sewer design guidelines. Uncertainty in the estimation of such properties will hence directly influence the dimensions of sewers, structures and pumps. In this paper the issue of potential trend and noise in the estimation is investigated for 6 rain series ranging from 19 to 55 years in duration. Different to recent research that predicts a climate induced-increase in heavy precipitation no clear indication for such trend was found in the investigated historical rain series. Another important aspect is the length of the rain series that is required for the estimation of extreme rainfall properties and the associated uncertainty. The analysis indicates that at least a period of 10 years should be used for the estimation. But even so the possible deviation expressed in terms of the 90 percentile is in the order of 5 to 10% of the 'true value', defined as the value derived when the whole given series is used for the estimation. 相似文献
12.
The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit. 相似文献
13.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
14.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture. 相似文献
15.
Thomy V. Dubois L. Vanoverschelde C. Sozanski J.P. Pribetich J. 《IEEE sensors journal》2004,4(6):772-778
This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented. 相似文献
16.
17.
On the effect of spatial variances in historical rainfall time series to CSO performance evaluation.
Historical, high-resolution rain series are the backbone of modern combined sewer overflow (CSO) structure design. These rain series are the input to the computational estimation of the performance of the measures with respect to CSO pollution abatement. However, those historical precipitation measurements are available at only a few locations. Frequently rain series have to be used from gauging stations at a significant distance. In order to judge and to compensate for this influence an estimate between rain characteristics and combined sewer outflow (CSO) performance indicators would be useful. In this paper such correlations have been sought for a collection of 37 rain series covering large areas of Europe. It was found that the mean annual rain volume can explain most of the variances for the performance indicators Number of overflows and CSO volume. For explaining the spatial differences in the efficiency of the CSO structure another rain characteristic, i.e. the maximum event with a return period of one year, is to be used. 相似文献
18.
为了分析多水库系统中两座水库之间灌溉用水的分配问题,建立了基到动态规划的神经网络模型。为了研究从一座上游水库取水在下游两座之库之间进行水量分配的问题,提出了3个状态变量和4个决策变量的改进的动态规划算法。采用神经网络模型,用3个状态变量动态规划算法得出调度原则,就所研究的多水库系统实例来说,新的动态规划神经网络模型的性能很好,将该模型的性能与临时凑合的标准调度原则和以前推荐使用的约束动态规划神经网络模型进行了比较。 相似文献
19.
G. I. Glazov A. M. Garaiev R. V. Timerkhanov 《Chemistry and Technology of Fuels and Oils》2003,39(1-2):26-53
A series of small–capacity units has recently been constructed in regions of oil field development and crude oil and gas condensate production to satisfy the requirements for such petroleum products as naphtha, diesel fuel, kerosene, and boiler fuel and to reduce costs for delivery of these products. There are almost no data in the technical literature, particularly in periodicals, on the construction and operation of small–capacity units. We attempt to generalize the experience of Orgeneftekhimzavody Trust in this area. We hope that this experience will be useful to specialists in the development and management of small–capacity plants. 相似文献
20.
A. V. Butko A. A. Klimov S. A. Nikitov Yu. A. Filimonov 《Journal of Communications Technology and Electronics》2006,51(8):944-947
The magneto-optical Kerr effect for red (628 nm) and green (532 nm) light is used to study magnetization processes in 2D magnonic crystals obtained by etching pits with the diameter D ≈ 32 μm to a depth of t ≤ 2 μm in a 16.1-μm-thick film of yttrium iron garnet (YIG). Hysteresis loops obtained in the case of the inplane crystal magnetization at 628 nm are characterized by lower saturation fields H s and higher remanent magnetizations than those obtained at 532 nm, a result that is attributed to different absorption coefficients of the YIG film at these wavelengths. This difference between the magnetization curves reflects the fact that the magnonic-crystal surface probed with the green light makes a greater contribution to the magneto-optical Kerr effect. Therefore, the green light is more sensitive to the demagnetizing fields, which govern magnetization processes in the magnonic crystals. 相似文献