全文获取类型
收费全文 | 5427篇 |
免费 | 261篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 82篇 |
综合类 | 27篇 |
化学工业 | 1596篇 |
金属工艺 | 102篇 |
机械仪表 | 100篇 |
建筑科学 | 329篇 |
矿业工程 | 23篇 |
能源动力 | 106篇 |
轻工业 | 509篇 |
水利工程 | 35篇 |
石油天然气 | 3篇 |
无线电 | 321篇 |
一般工业技术 | 1120篇 |
冶金工业 | 493篇 |
原子能技术 | 41篇 |
自动化技术 | 814篇 |
出版年
2023年 | 40篇 |
2022年 | 52篇 |
2021年 | 93篇 |
2020年 | 83篇 |
2019年 | 75篇 |
2018年 | 91篇 |
2017年 | 116篇 |
2016年 | 167篇 |
2015年 | 125篇 |
2014年 | 182篇 |
2013年 | 281篇 |
2012年 | 259篇 |
2011年 | 342篇 |
2010年 | 264篇 |
2009年 | 272篇 |
2008年 | 260篇 |
2007年 | 246篇 |
2006年 | 244篇 |
2005年 | 206篇 |
2004年 | 178篇 |
2003年 | 144篇 |
2002年 | 113篇 |
2001年 | 88篇 |
2000年 | 95篇 |
1999年 | 101篇 |
1998年 | 124篇 |
1997年 | 87篇 |
1996年 | 91篇 |
1995年 | 70篇 |
1994年 | 72篇 |
1993年 | 76篇 |
1992年 | 73篇 |
1991年 | 57篇 |
1990年 | 59篇 |
1989年 | 56篇 |
1988年 | 60篇 |
1987年 | 54篇 |
1986年 | 47篇 |
1985年 | 46篇 |
1984年 | 54篇 |
1983年 | 39篇 |
1982年 | 47篇 |
1981年 | 47篇 |
1980年 | 32篇 |
1979年 | 31篇 |
1978年 | 34篇 |
1977年 | 32篇 |
1976年 | 33篇 |
1975年 | 37篇 |
1973年 | 31篇 |
排序方式: 共有5701条查询结果,搜索用时 15 毫秒
1.
2.
This DFG-funded research project aimed to gain a better understanding of the mechanisms of the W-Cl repair principle within the framework of fundamental investigations, to contribute to the creation of the necessary basis for a broader application of the repair principle in practice. The focus was on the development of a model to describe the chloride redistribution after the application of a system sealing surface protective coating. On the basis of Fick's second law of diffusion, a mathematical model with a self-contained analytical solution was developed, with the help of which the chloride redistribution after application of a system sealing surface protective coating can be calculated under the idealized assumption of complete water saturation of the concrete. Furthermore, the influence of the dehydration of the concrete, expected as a result of the application of the repair principle W-Cl, on the chloride redistribution was investigated. On the basis of laboratory tests and numerical simulations, material-specific reduction functions were developed to quantify the relationship between the chloride diffusion coefficient and the ambient humidity. 相似文献
3.
A heavy crude oil has been treated with deuterated alkylating reagents (CD3I and C2D5I) and directly analyzed without any prior fractionation and chromatographic separation by high-field Orbitrap Fourier Transform Mass Spectrometry (FTMS) and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) using electrospray ionization (ESI). The reaction of a polycyclic aromatic sulfur heterocycles (PASHs) dibenzothiophene (DBT), in the presence of silver tetrafluoroborate (AgBF4) with ethyl iodide (C2H5I) in anhydrous dichloroethane (DCE) was optimized as a sample reaction to study heavy crude oil mixtures, and the reaction yield was monitored and determined by proton nuclear magnetic resonance spectroscopy (1H-NMR). The obtained conditions were then applied to a mixture of standard aromatic CH-, N-, O- and S-containing compounds and then a heavy crude oil, and only sulfur-containing compounds were selectively alkylated. The deuterium labeled alkylating reagents, iodomethane-d3 (CD3I) and iodoethane-d5 (C2D5I), were employed to the alkylation of heavy crude oil to selectively differentiate the tagged sulfur species from the original crude oil. 相似文献
4.
5.
Wolfgang Wendler 《电子产品世界》2006,(17):129-130
与美国同行争分夺秒抢占市场先机不同,欧洲测量仪器厂商Rohde&Schwarz公司的产品策略则相对稳健,他们的产品更专注于功能的多样化 相似文献
6.
7.
8.
Ohne Zusammenfassung 相似文献
9.
Larissa Canilha Walter Carvalho Marco Giulietti Maria Das Graças Almeida Felipe João Batista Almeida E Silva 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):715-721
BACKGROUND: Xylitol bioproduction from lignocellulosic residues comprises hydrolysis of the hemicellulose, detoxification of the hydrolysate, bioconversion of the xylose, and recovery of xylitol from the fermented hydrolysate. There are relatively few reports on xylitol recovery from fermented media. In the present study, ion‐exchange resins were used to clarify a fermented wheat straw hemicellulosic hydrolysate, which was then vacuum‐concentrated and submitted to cooling in the presence of ethanol for xylitol crystallization. RESULTS: Sequential adsorption into two anion‐exchange resins (A‐860S and A‐500PS) promoted considerable reductions in the content of soluble by‐products (up to 97.5%) and in medium coloration (99.5%). Vacuum concentration led to a dark‐colored viscous solution that inhibited xylitol crystallization. This inhibition could be overcome by mixing the concentrated medium with a commercial xylitol solution. Such a strategy led to xylitol crystals with up to 95.9% purity. The crystallization yield (43.5%) was close to that observed when using commercial xylitol solution (51.4%). CONCLUSION: The experimental data demonstrate the feasibility of using ion‐exchange resins followed by cooling in the presence of ethanol as a strategy to promote the fast recovery and purification of xylitol from hemicellulose‐derived fermentation media. Copyright © 2008 Society of Chemical Industry 相似文献
10.
Types of crystallizers . In the industrial application of single mass crystallization from solution clear aims exist with regard to crystallizate qualities. To fulfil these aims, one can choose between various types of crystallizers. Magma types, i.e. agitated tank crystallizer, forced circulation and draft tube (baffle) crystallizer, as well as classifying types with the well-known Oslo-crystallizer belong to the present state of the art. The rates of secondary nucleation decrease in the same sequence as that given above and the possibilities of influencing crystal size distributions increase, and coarser crystals are produceable. 相似文献