全文获取类型
收费全文 | 11068篇 |
免费 | 1050篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 85篇 |
综合类 | 8篇 |
化学工业 | 2784篇 |
金属工艺 | 126篇 |
机械仪表 | 335篇 |
建筑科学 | 506篇 |
矿业工程 | 23篇 |
能源动力 | 243篇 |
轻工业 | 2283篇 |
水利工程 | 101篇 |
石油天然气 | 21篇 |
无线电 | 836篇 |
一般工业技术 | 2119篇 |
冶金工业 | 574篇 |
原子能技术 | 30篇 |
自动化技术 | 2056篇 |
出版年
2024年 | 21篇 |
2023年 | 158篇 |
2022年 | 137篇 |
2021年 | 375篇 |
2020年 | 310篇 |
2019年 | 314篇 |
2018年 | 485篇 |
2017年 | 487篇 |
2016年 | 578篇 |
2015年 | 447篇 |
2014年 | 582篇 |
2013年 | 1059篇 |
2012年 | 1024篇 |
2011年 | 924篇 |
2010年 | 583篇 |
2009年 | 547篇 |
2008年 | 608篇 |
2007年 | 556篇 |
2006年 | 445篇 |
2005年 | 318篇 |
2004年 | 301篇 |
2003年 | 256篇 |
2002年 | 247篇 |
2001年 | 140篇 |
2000年 | 140篇 |
1999年 | 98篇 |
1998年 | 107篇 |
1997年 | 92篇 |
1996年 | 81篇 |
1995年 | 74篇 |
1994年 | 76篇 |
1993年 | 61篇 |
1992年 | 39篇 |
1991年 | 32篇 |
1990年 | 20篇 |
1989年 | 25篇 |
1988年 | 25篇 |
1987年 | 14篇 |
1986年 | 19篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1983年 | 20篇 |
1982年 | 21篇 |
1981年 | 25篇 |
1980年 | 17篇 |
1979年 | 27篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1973年 | 11篇 |
1947年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 456 毫秒
31.
32.
Paulo S. André António L. Teixeira Armando N. Pinto Lara P. Pellegrino Berta B. Neto José F. Rocha Joäo L. Pinto Paulo N. Monteiro 《ETRI Journal》2006,28(2):257-259
In this letter, we will evaluate the performance degradation of a 40 km high‐speed (40 Gb/s) optical system, induced by optical fiber variations of the chromatic dispersion induced by temperature changes. The chromatic dispersion temperature sensitivity will be estimated based on the signal quality parameters. 相似文献
33.
34.
Susana Criado Norman A. García Maria I. Gutirrez Vicente Avila Sonia G. Bertolotti Rio Cuarto 《European Journal of Lipid Science and Technology》1996,98(5):172-175
The ability of mono-, di-, tri-and tetra-hydroxyflavones (7-and 3-hy-droxyflavones, 7, 8-dihydroxyflavone, baicalein and fisetin) to act as photoprotectors against singlet molecular oxygen [O2(Δg)]-initiated photooxidation of fats has been established by a kinetic study. The overall quenching rate constants for a series of five hydroxyflavones perfectly parallel their respective behaviour as inhibitors of the sensitized photooxidation of linoleic acid. The best antioxidative effect was exerted by 7-hydroxyflavone which does not chemically react with O2(1Δg). Nevertheless for the remaining flavonoids of the series, the physical deactivation of O2(1Δg) largely prevails over the chemical process. As for the cases of phenols and related hydroxy-aromatic derivatives, the ionization of the -OH group in the flavones, dramatically accelerates the rate of photooxidation. Under these conditions, the 7-hydroxyflavone also reacts effectively with O2(1Δg). Given that flavonoids are natural oil components, this medium effect should be taken into account during the oil-refining process, in order to avoid the flavonoid photodestruction. 相似文献
35.
José Martínez-Aroza Ramón Román-Roldán 《Multidimensional Systems and Signal Processing》1995,6(1):7-35
A multiresolution analysis of digital gray-level images is presented. A gray-level multi-scale framework is determined from two main assumptions: the gray scale is binary at the finest spatial resolution, and the gray levels of composed regions are obtained additively. In order to interrelate the gray-level histograms of the same image at different resolutions, probabilistic linear models are developed, which are then applied for estimation. Linear-optimization theory is used as a way of constructing such models. A general procedure for image processing is sketched, based on gray-level estimation. A versatile algorithm for nonlinear filtering is derived. Some examples of prospective applications are given.This work was partially supported by grant TIC91-646 from the DGYCIT of the Spanish Government. 相似文献
36.
37.
38.
The first stages of nickel electrodeposition on amorphous carbon and polycrystalline silver substrates have been studied under galvanostatic conditions. An island growth mode is observed on the two types of substrate. For equivalent conditions the cluster density is higher on silver substrates than on carbon substrates. Dissolution of some nickel clusters is observed a short time after the onset of electrolysis on carbon substrates. This is confirmed by the evolution of the current efficiency and the evolution of the metal surface cluster density as a function of the quantity of electricity. 相似文献
39.
Antonio J. Pérez-López José Manuel López-Nicolás Angel A. Carbonell-Barrachina 《European Food Research and Technology》2007,225(2):255-260
Consumers demand organic products because they believe that the organic products are more flavorful and respectful to the
environment and human health. The effects of organic farming on the minerals contents and aroma composition of Clemenules
mandarin juices were studied. Minerals (Fe, Cu, Mn, Zn, Ca, Mg, K, and Na) were quantified using atomic absorption-emission
spectroscopy, while volatile compounds were extracted using the dynamic headspace technique and were identified and quantified
by GC–MS. In general, organic farming produced a mandarin juice with a higher quality than that produced by conventional agricultural
practices. Higher concentrations of both minerals and positive volatile compounds were found in the organic juice, while the
formation of off-flavors was higher in the conventional juice, although threshold values were not reached. 相似文献
40.