全文获取类型
收费全文 | 1318篇 |
免费 | 59篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 15篇 |
综合类 | 2篇 |
化学工业 | 368篇 |
金属工艺 | 19篇 |
机械仪表 | 35篇 |
建筑科学 | 63篇 |
矿业工程 | 2篇 |
能源动力 | 39篇 |
轻工业 | 140篇 |
水利工程 | 9篇 |
石油天然气 | 1篇 |
无线电 | 115篇 |
一般工业技术 | 194篇 |
冶金工业 | 71篇 |
原子能技术 | 11篇 |
自动化技术 | 298篇 |
出版年
2023年 | 16篇 |
2022年 | 47篇 |
2021年 | 60篇 |
2020年 | 24篇 |
2019年 | 27篇 |
2018年 | 33篇 |
2017年 | 33篇 |
2016年 | 57篇 |
2015年 | 30篇 |
2014年 | 39篇 |
2013年 | 97篇 |
2012年 | 82篇 |
2011年 | 93篇 |
2010年 | 68篇 |
2009年 | 74篇 |
2008年 | 61篇 |
2007年 | 65篇 |
2006年 | 62篇 |
2005年 | 48篇 |
2004年 | 48篇 |
2003年 | 37篇 |
2002年 | 37篇 |
2001年 | 19篇 |
2000年 | 17篇 |
1999年 | 15篇 |
1998年 | 26篇 |
1997年 | 27篇 |
1996年 | 13篇 |
1995年 | 18篇 |
1994年 | 19篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1963年 | 1篇 |
1903年 | 1篇 |
排序方式: 共有1382条查询结果,搜索用时 15 毫秒
101.
102.
The UV spectra of tungsten oxide catalysts supported on alumina, titania and zirconia, and on titania–alumina and titania–zirconia
mixed oxides are reported and discussed. Evidence is provided for the different electronic structure of supports and catalysts,
which could affect the behavior of the tungsten oxide centres in the different cases. On alumina, tungsten oxide centres are
“isolated” by the insulating support, while on titania-based materials they are likely in electronic contact with each other
and with Ti centres through the support conduction band. In the case of WOx2013;ZrO2, the 5d levels of tungsten ions fall just below of the lower energy limit of the support conduction band.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
103.
Guido Schryen 《欧洲信息系统杂志》2013,22(2):139-169
The business value of investments in Information Systems (IS) has been, and is predicted to remain, one of the major research topics for IS researchers. While the vast majority of research papers on IS business value find empirical evidence in favour of both the operational and strategic relevance of IS, the fundamental question of the causal relationship between IS investments and business value remains partly unexplained. Three research tasks are essential requisites on the path towards addressing this epistemological question: the synthesis of existing knowledge, the identification of a lack of knowledge and the proposition of paths for closing the knowledge gaps. This paper considers each of these tasks. Research findings include that correlations between IS investments and productivity vary widely among companies and that the mismeasurement of IS investment impact may be rooted in delayed effects. Key limitations of current research are based on the ambiguity and fuzziness of IS business value, the neglected disaggregation of IS investments, and the unexplained process of creating internal and competitive value. Addressing the limitations we suggest research paths, such as the identification of synergy opportunities of IS assets, and the explanation of relationships between IS innovation and change in IS capabilities. 相似文献
104.
Summary. In this paper we introduce and analyze two new cost measures related to the communication overhead and the space requirements
associated with virtual path layouts in ATM networks, that is the edge congestion and the node congestion. Informally, the edge congestion of a given edge e at an incident node u is defined as the number of VPs terminating at or starting from u and using e, while the node congestion of a node v is defined as the number of VPs having v as an endpoint. We investigate the problem of constructing virtual path layouts allowing to connect a specified root node
to all the others in at most h hops and with maximum edge or node congestion c, for two given integers h and c. We first give tight results concerning the time complexity of the construction of such layouts for both the two congestion
measures, that is we exactly determine all the tractable and intractable cases. Then, we provide some combinatorial bounds
for arbitrary networks, together with optimal layouts for specific topologies such as chains, rings and grids.
Received: December 1997 / Accepted: August 2000 相似文献
105.
Guido Notermans Anco Heringa Maarten van Dort Sander Jansen Fred Kuper 《Microelectronics Reliability》2000,40(1):117
In this paper a new model for localized breakdown in NMOSTs under ESD stress is developed, which accounts for the reduced ESD strength in silicided devices. The model explains the impact of a stabilizing drain resistance on second breakdown current for both silicided and unsilicided protections. 相似文献
106.
Empirical evidence for effects of moods (both naturally occurring and experimentally manipulated) on behavior is reviewed in terms of an integrative theory: the mood-behavior model (MBM). It is posited that moods can influence behavior via 2 processes: (a) by informational effects on behavior-related judgments and appraisals, which in turn will result in behavioral adjustments (i.e., the informational mood impact on behavior), and (b) by influencing behavioral preferences and interests in compliance with a hedonic motive (i.e., the directive mood impact on behavior). The strength of the informational mood impact depends on moods' effective informational weight for behavior-related judgments and on mood-primed associations. The strength of the directive mood impact is predicted to be jointly determined by 2 variables: the strength of a hedonic motive and the instrumentality of possible acts for affect regulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
107.
108.
J. S. Major L. J. Guido N. Holonyak K. C. Hsieh E. J. Vesely D. W. Nam D. C. Hall J. E. Baker P. Gavrilovic K. Meehan W. Stutius J. E. Williams 《Journal of Electronic Materials》1990,19(1):59-66
In these experiments impurity-induced layer disordering (IILD) utilizing chemical reduction of SiO2 by Al (from Al0.8Ga0.2As) is employed to generate Si and O to effect layer disordering. The SiO2-Al0.8Ga0.2As reaction is studied with respect to annealing ambient. By controlling the extent of disordering via As4 overpressure, closely spaced (∼1μm) Si-O IILD buried heterostructure lasers can be optically coupled or uncoupled. Direct observation of O incorporation into
the buried layers is shown using secondary ion mass spectroscopy (SIMS). The thermal stability of separate-confinement AlyGa1−yAs-GaAs-InxGa1−xAs quantum well heterostructure (QWH) laser crystals is investigated using SIMS, transmission electron microscopy (TEM), and
photoluminescence (PL) measurements. The data show that the thermal stability of a strained-layer In0.1Ga0.9As quantum well (QW) is strongly dependent upon: (1) the layer thickness and heterointerfaces of the AlyGa1−yAs-GaAs waveguide layers located directly above and below the QW, (2) the type of surface encapsulant employed, and (3) the
annealing ambient. Narrow single-stripe (<2μm) lasers fabricated via Si-O diffusion and layer disordering exhibit low threshold currents (Ith ∼ 4 mA) and differential quantum efficiencies,η, of 22% per facet under continuous (cw) room-temperature operation. 相似文献
109.
An IR study of thermally stable V2O5-WO3 -TiO2 SCR catalysts modified with silica and rare-earths (Ce, Tb, Er) 总被引:1,自引:0,他引:1
Maria Angeles Larrubia Vargas Marzia Casanova Alessandro Trovarelli Guido Busca 《Applied catalysis. B, Environmental》2007,75(3-4):303-311
The catalytic activity of silica-free and silica-modified rare earth (Ce, Tb, Er) containing V2O5-WO3 -TiO2 catalysts in the selective catalytic reduction of NO by ammonia has been investigated as a function of ageing temperatures. The adsorption of ammonia on the catalysts and the behavior of their surface hydroxy groups and of bulk vibrations has also been studied by IR spectroscopy. Rare earths slightly decrease the catalytic activity of catalysts in a fresh state, and this has been attributed to the perturbation, observed by IR, of the vanadyl groups with a likely lowering of their Lewis acidity. However, rare earths (in particular Tb and Er) increase strongly the catalytic activity of catalysts after ageing. Silica only does not seem to have a positive effect on thermal stability and activity when vanadium is present. It has been concluded that rare earths strongly increase the thermal resistance of the catalysts and inhibit rutilization and surface area loss because they do not penetrate the anatase bulk while tend to cover the external surface. In addition the negative action of free vanadium on phase stability is decreased due to formation of rare earth vanadates. 相似文献
110.
Barbara Jaskula Koen Goiris Gert De Rouck Guido Aerts Luc De Cooman 《Journal of the Institute of Brewing》2007,113(4):381-390
A pleasant and consistent bitterness is an essential flavour attribute of beer. Hop‐derived iso‐α‐acids are largely responsible for beer bitterness and accurate determination of these primary flavour compounds is very important in relation to quality control. The most widely used way to determine beer bitterness is based on spectrophotometry, measuring the absorbance of an iso‐octane extract of acidified beer. However, this approach is far from specific as it measures all of the extracted compounds, including non‐bittering principles. For that particular reason, High Performance Liquid Chromatography (HPLC) is increasingly applied for the quantitative determination of hop‐derived iso‐α‐acids and, if present, reduced iso‐α‐acids. However, to obtain accurate data on beer bitterness profiles, both quantitative sample preparation and state‐of‐the‐art HPLC are essential. In this paper, several extraction procedures based on solid phase extraction (SPE) and liquid‐liquid extraction (LLE), respectively, were evaluated and an optimised extraction methodology using H3PO4 for sample acidification prior to extraction is presented. The proposed extraction/HPLC methodology allows for the quantitative recovery and analysis of hop‐derived beer bitterness. 相似文献