全文获取类型
收费全文 | 22719篇 |
免费 | 3674篇 |
国内免费 | 2573篇 |
专业分类
电工技术 | 1817篇 |
技术理论 | 4篇 |
综合类 | 2601篇 |
化学工业 | 1066篇 |
金属工艺 | 250篇 |
机械仪表 | 779篇 |
建筑科学 | 4316篇 |
矿业工程 | 1658篇 |
能源动力 | 455篇 |
轻工业 | 817篇 |
水利工程 | 823篇 |
石油天然气 | 737篇 |
武器工业 | 211篇 |
无线电 | 2575篇 |
一般工业技术 | 1516篇 |
冶金工业 | 538篇 |
原子能技术 | 94篇 |
自动化技术 | 8709篇 |
出版年
2024年 | 134篇 |
2023年 | 471篇 |
2022年 | 885篇 |
2021年 | 1085篇 |
2020年 | 1033篇 |
2019年 | 781篇 |
2018年 | 765篇 |
2017年 | 882篇 |
2016年 | 932篇 |
2015年 | 1021篇 |
2014年 | 1595篇 |
2013年 | 1389篇 |
2012年 | 1794篇 |
2011年 | 1902篇 |
2010年 | 1510篇 |
2009年 | 1513篇 |
2008年 | 1482篇 |
2007年 | 1696篇 |
2006年 | 1380篇 |
2005年 | 1214篇 |
2004年 | 957篇 |
2003年 | 828篇 |
2002年 | 732篇 |
2001年 | 555篇 |
2000年 | 499篇 |
1999年 | 399篇 |
1998年 | 283篇 |
1997年 | 214篇 |
1996年 | 191篇 |
1995年 | 166篇 |
1994年 | 147篇 |
1993年 | 93篇 |
1992年 | 65篇 |
1991年 | 57篇 |
1990年 | 46篇 |
1989年 | 37篇 |
1988年 | 26篇 |
1987年 | 28篇 |
1986年 | 23篇 |
1985年 | 21篇 |
1984年 | 19篇 |
1983年 | 21篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1975年 | 4篇 |
1958年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
71.
72.
Wood has long traditions as a building material, and is often used in construction elements, and as interior and exterior surfaces in the Nordic countries. In most applications, there are reaction to fire requirements to products used as surfaces, e.g. in escape routes and larger public spaces. Most wood products will therefore have to be treated with fire retardant (FR) agents to fulfil the strict requirements to properties connected to heat release and flame spread. Unfortunately, FR agents usually also increase the smoke production, as they cause a more incomplete combustion of the wood. The wood product manufacturers seek to find the optimal amount of FR additives where both heat release and smoke production in the classifying test are within the requirements given in the building regulations. This paper describes models for prediction of the European reaction to fire classes of wood products. The models are based on multivariate statistical analysis, and use test results from the cone calorimeter test as input. The presented models are, with very good precision, able to predict which Euroclass and additional smoke class a wood based product would obtain if it were to be tested in the single burning item test. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
73.
R. D. Dupuis J. C. Bean J. M. Brown A. T. Macrander R. C. Miller L. C. Hopkins 《Journal of Electronic Materials》1987,16(1):69-77
We report the results of studies which have been made on heteroepitaxial layers of GaAs and AlGaAs grown by metalorganic chemical
vapor deposition on composite substrates that consist of four different types of heteroepitaxial layered structures of Ge
and Ge-Si grown by molecular beam epitaxy on (100)-oriented Si substrates. It is found that of the four structures studied,
the preferred composite substrate is a single layer of Ge ∼1 μm thick grown directly on a Si buffer layer. The double-crystal
X-ray rocking curves of 2 μm thick GaAs films grown on such substrates have FWHM values as small as 168 arc sec. Transmission
electron micrographs of these Ge/Si composite substrates has shown that the number of dislocations in the Ge heteroepitaxial
layer can be greatly reduced by an anneal at about 750° C for 30 min which is simultaneously carried out during the growth
of the GaAs layer. The quality of the GaAs layers grown on these composite substrates can be greatly improved by the use of
a five-period GaAs-GaAsP strained-layer superlattice (SLS). Using the results of these studies, low-threshold optically pumped
AlGaAs-GaAs DH laser structures have been grown by MOCVD on MBE Ge/Si composite substrates. 相似文献
74.
以某条软土地层中开挖的地铁隧道为例,根据非线性有限元法的基本原理,利用大型非线性有限元软件ADINA三维动态模拟地铁隧道开挖过程,计算结果揭示了在盾构推进过程中地表沉降分布以及特点,得到盾构法开挖引起的地表沉降曲线,其形态与Peck计算得出的横向地表沉降槽正态分布曲线的形态基本一致,隧道轴线正上方地表沉降最为明显。 相似文献
75.
In this paper, we propose an approach that combines the unsupervised and supervised learning techniques for unconstrained
handwritten numeral recognition. This approach uses the Kohonen self-organizing neural network for data classification in
the first stage and the learning vector quantization (LVQ) model in the second stage to improve classification accuracy. The
combined architecture performs better than the Kohonen self-organizing map alone. In the proposed approach, the collection
of centroids at different phases of training plays a vital role in the performance of the recognition system. Four experiments
have been conducted and experimental results show that the collection of centroids in the middle of the training gives high
performance in terms of speed and accuracy. The systems developed also resolve the confusion between handwritten numerals. 相似文献
76.
优化印制电路板地线设计 总被引:1,自引:0,他引:1
印制电路板地线是印制电路板设计的一个基本问题,本文详细分析了印制电路板地线对电路的干扰,介绍了减小地线对电路干扰的方法,阐述了印制电路板地线的设计规则,将其应用到实际的印制电路板设计中,可大大提高印制电路板的抗干扰能力,实现电磁兼容。 相似文献
77.
Ran-Rong Lee 《Journal of the American Ceramic Society》1991,74(9):2242-2249
AIN ceramics with densities varying from 3.18 to 3.30 g/cm3 and room-temperature thermal conductivities varying from 88 to 193 W/m K were produced. Different sintering conditions, packing powders, AIN powder sources, carbon additive, and sintering times were evaluated, and the key processing parameters which cause the differences in density and thermal conductivity were identified. SEM, TEM, and EDS were used to characterize the correlation between thermal conductivity, microstructure, and processing parameters. The important parameters which control the thermal conductivity of AIN ceramics are discussed. 相似文献
78.
Ground rubber tire (GRT) powder was maleated in an internal mixer using maleic anhydride and dicumyl peroxide at 160°C. Maleated GRT was characterized by using X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, wettability, and differential scanning calorimetry. The physical properties of the dynamically vulcanized 60 : 40, rubber : plastic composition based on acrylated high‐density polyethylene as the plastic phase and ethylene propylene diene rubber containing maleated GRT as the rubber phase were found to be greater than the corresponding composition containing nonmaleated GRT. The blend was found to be reprocessable, like themoplastic elastomers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 370–378, 2002; DOI 10.1002/app.10348 相似文献
79.
从文献分类的实践出发,提出了对计算机技术图书分类标引工作存在的问题,分析了问题的原因,提出了解决问题的方法。 相似文献
80.