全文获取类型
收费全文 | 5790篇 |
免费 | 358篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 76篇 |
综合类 | 13篇 |
化学工业 | 1494篇 |
金属工艺 | 138篇 |
机械仪表 | 115篇 |
建筑科学 | 402篇 |
矿业工程 | 29篇 |
能源动力 | 147篇 |
轻工业 | 452篇 |
水利工程 | 50篇 |
石油天然气 | 8篇 |
无线电 | 452篇 |
一般工业技术 | 1232篇 |
冶金工业 | 247篇 |
原子能技术 | 37篇 |
自动化技术 | 1261篇 |
出版年
2024年 | 11篇 |
2023年 | 102篇 |
2022年 | 140篇 |
2021年 | 229篇 |
2020年 | 150篇 |
2019年 | 128篇 |
2018年 | 190篇 |
2017年 | 165篇 |
2016年 | 248篇 |
2015年 | 242篇 |
2014年 | 302篇 |
2013年 | 400篇 |
2012年 | 379篇 |
2011年 | 463篇 |
2010年 | 357篇 |
2009年 | 340篇 |
2008年 | 341篇 |
2007年 | 317篇 |
2006年 | 242篇 |
2005年 | 211篇 |
2004年 | 160篇 |
2003年 | 149篇 |
2002年 | 126篇 |
2001年 | 81篇 |
2000年 | 78篇 |
1999年 | 66篇 |
1998年 | 75篇 |
1997年 | 45篇 |
1996年 | 49篇 |
1995年 | 57篇 |
1994年 | 34篇 |
1993年 | 33篇 |
1992年 | 29篇 |
1991年 | 21篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 5篇 |
排序方式: 共有6153条查询结果,搜索用时 15 毫秒
31.
Stefan Yoshi Buhmann Hassan Safari Dirk-Gunnar Welsch Ho Trung Dung 《Open Systems & Information Dynamics》2006,13(4):427-436
We establish a general relation between dispersion forces. First, based on QED in causal media, leading-order perturbation theory is used to express both the single-atom Casimir-Polder and the two-atom van der Waals potentials in terms of the atomic polarizabilities and the Green tensor for the body-assisted electromagnetic field. Endowed with this geometry-independent framework, we then employ the Born expansion of the Green tensor together with the Clausius-Mosotti relation to prove that the macroscopic Casimir-Polder potential of an atom in the presence of dielectric bodies is due to an infinite sum of its microscopic many-atom van der Waals interactions with the atoms comprising the bodies. This theorem holds for inhomogeneous, dispersing, and absorbing bodies of arbitrary shapes and arbitrary atomic composition on an arbitrary background of additional magnetodielectric bodies. 相似文献
32.
XML hat sich als Sprache zur Definition von Dokumenten für den universellen Datenaustausch etabliert. XML-Schema erm?glicht
ausgefeilte Definitionen für XML-Dokumente und hat beste Chancen, die bisher eingesetzte DTD abzul?sen. Neben einer allgemeinen
Einführung geht dieser Beitrag auch auf verfügbare Produkte und neue M?glichkeiten der objektorientierten Softwareentwicklung
mit XML-Schema ein.
Vorschl?ge an Prof. Dr. Frank Puppe <puppe@informatik.uni-wuerzburg.de> oder Dieter Steinbauer <dieter.steinbauer@schufa.de>
Alle „Aktuellen Schlagw?rter” seit 1988 finden Sie unter: www.ai-wuerzburg.de/as 相似文献
33.
Studies on the influence of anthracene coal extracts on the carbonization process of medium- and high-rank coals were undertaken. Extracts from flame coal (Int. Class. 900) and gas-coking coal (Int. Class. 632) were used as additives. The blends prepared from the examined coals and the extracts exhibited better coking properties than the parent coals. The addition of extract to the coals gave an increase in the microstrength of the resultant cokes. The effects of co-carbonization of coking coals with extracts were increases in the size of the optical texture as well as in the degree of structural ordering of cokes. In the co-carbonization of semicoking coal with addition of coal extracts, a reduction in the size of the anisotropic units and a decrease in the crystallite height of cokes were observed. No modification of the basic anisotropy of coke from anthracite by coal extract was observed. With increasing extract content in anthracite/extract blends there was an increase in the degree of structural ordering of co-carbonization products. Extract addition was unable to modify the behaviour of fusinite. Based on the results of investigation of the influence of coal extracts on the carbonization of different-rank coals, a division of coals according to the modification of the optical texture of coke is given. 相似文献
34.
35.
36.
Odors seem to be perceived differently when presented ortho- or retronasally. In this study, stimuli of controlled concentration and duration were applied in either the anterior nasal cavity or epipharynx by means of air-dilution olfactometry. Stimulus concentration was monitored in the olfactory cleft. In Experiment 1, odor thresholds to a food (chocolate) and a nonfood (lavender) odor were lower for orthonasal, compared with retronasal, stimulation. In Experiment 2, intensity ratings to suprathreshold odor concentrations were significantly higher for orthonasal than for retronasal stimulation with hydro- hydrogen sulfide, but not phenyl ethyl alcohol. Accordingly, amplitudes and latencies of olfactory event-related gen potentials to retronasal stimuli were found to be smaller and prolonged, respectively. This indicates differential processing of olfactory stimuli presented through the retronasal or orthonasal routes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
37.
In this paper, we present the findings from an extensive study of the use of virtual reality (VR) models in large construction projects. The study includes two parts: The first part presents a quantitative questionnaire designed to investigate how VR models are experienced and assessed by the workforce at a building site. The second part includes a qualitative field survey of how VR models can be applied and accepted by professionals in the design and planning process of a large pelletizing plant. Through mainly studying persons who had little or no experience with advanced information technology (IT), we hoped to reveal the attitudes of the average person working at a construction site rather than of an IT expert. In summary, the study shows that the VR models in both projects have been very useful and well accepted by the users. Today’s information flow is, from a general point of view, considered to be insufficient and the hypothesis is that using VR models in the construction process have the potential to minimize waste of resources and improve the final result. 相似文献
38.
Packed beds of fuel wood chips are commonly found in thermal conversion processes such as combustion or gasification. Wood chips in particular are mostly used as fuel for small-scale domestic heating boilers but also for commercial-scale combustion units. The characterization of spatial voidage distribution inside the wood chip beds is of great importance for flow and reactor modelling. This study focuses on the radial porosity variations of cylindrical beds of three different types of commercially available wood chips including chips classified as G30 size class. The conventional technique of consolidating packed beds with a resin was chosen as the experimental procedure. The radial voidage distribution in different cylindrical beds is determined by image analysis of sections of the solidified packings. Additionally, a packing of monosized spheres was investigated in order to assess the selected procedure in comparison with widely available literature data for spheres. The results are discussed and summarized in a mathematical expression correlating the radial voidage distribution depending on average wood chip size, packing core porosity and dimensionless distance from the tube wall. 相似文献
39.
40.
We propose an exact algorithm for counting the models of propositional formulas in conjunctive normal form. Our algorithm is based on the detection of strong backdoor sets of bounded size; each instantiation of the variables of a strong backdoor set puts the given formula into a class of formulas for which models can be counted in polynomial time. For the backdoor set detection we utilize an efficient vertex cover algorithm applied to a certain “obstruction graph” that we associate with the given formula. This approach gives rise to a new hardness index for formulas, the clustering-width. Our algorithm runs in uniform polynomial time on formulas with bounded clustering-width. It is known that the number of models of formulas with bounded clique-width, bounded treewidth, or bounded branchwidth can be computed in polynomial time; these graph parameters are applied to formulas via certain (hyper)graphs associated with formulas. We show that clustering-width and the other parameters mentioned are incomparable: there are formulas with bounded clustering-width and arbitrarily large clique-width, treewidth, and branchwidth. Conversely, there are formulas with arbitrarily large clustering-width and bounded clique-width, treewidth, and branchwidth. 相似文献