全文获取类型
收费全文 | 492篇 |
免费 | 45篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 195篇 |
金属工艺 | 13篇 |
机械仪表 | 11篇 |
建筑科学 | 10篇 |
能源动力 | 9篇 |
轻工业 | 112篇 |
水利工程 | 4篇 |
石油天然气 | 1篇 |
无线电 | 27篇 |
一般工业技术 | 57篇 |
冶金工业 | 34篇 |
自动化技术 | 63篇 |
出版年
2023年 | 11篇 |
2022年 | 45篇 |
2021年 | 44篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 29篇 |
2015年 | 20篇 |
2014年 | 23篇 |
2013年 | 32篇 |
2012年 | 27篇 |
2011年 | 27篇 |
2010年 | 25篇 |
2009年 | 23篇 |
2008年 | 19篇 |
2007年 | 27篇 |
2006年 | 17篇 |
2005年 | 15篇 |
2004年 | 13篇 |
2003年 | 13篇 |
2002年 | 14篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有538条查询结果,搜索用时 312 毫秒
41.
42.
Laguerre-Gauss and Bessel-Gauss beams in uniaxial crystals 总被引:1,自引:0,他引:1
Cincotti G Ciattoni A Palma C 《Journal of the Optical Society of America. A, Optics, image science, and vision》2002,19(8):1680-1688
A simple correspondence between the paraxial propagation formulas along the optical axis of a uniaxial crystal and inside an isotropic medium is found in the case of beams with linearly polarized circularly symmetric boundary distributions. The electric fields of the ordinary and the extraordinary beams are related to the corresponding expressions in a medium with refractive index n(o) and n(e)2/n(o), where n(o) and n(e) are the ordinary and the extraordinary refractive indexes, respectively. Closed-form expressions for Laguerre-Gauss and Bessel-Gauss beams propagating through an anisotropic crystal are given. 相似文献
43.
Byström JU Hansson GA Rylander L Ohlsson K Källrot G Skerfving S 《Applied ergonomics》2002,33(1):63-74
The aim was to evaluate (1) the physical workload on neck and upper limb in computer-aided design (CAD) work; (2) the impact of two applications (PROFESSIONAL-CADAM and PRO/Engineering) and (3) two input devices (computer mouse and keyboard), as well as (4) sitting and standing work positions. Fifteen CAD operators were interviewed and examined physically. For nine subjects, the physical workload was measured: electromyography (EMG) of trapezius and forearm extensor muscles, inclinometry of the head, the upper back and upper arms, as well as wrist goniometry. The muscular load was low in CAD work, but the inter-individual variation was considerable. Neither the positions were extreme, nor the movements. The applications, per se, did not have a large impact on the workload, but because of the need for different input devices the effect was strong. Using a keyboard meant higher angular velocities than using a mouse. Hence, when choosing a new software, which requires mainly a mouse as input device, this has to be balanced against the risk of disorders. 相似文献
44.
A syntax-preserving error resilience tool for JPEG 2000 based on error correcting arithmetic coding. 总被引:3,自引:0,他引:3
Marco Grangetto Enrico Magli Gabriella Olmo 《IEEE transactions on image processing》2006,15(4):807-818
JPEG 2000 is the novel ISO standard for image and video coding. Besides its improved coding efficiency, it also provides a few error resilience tools in order to limit the effect of errors in the codestream, which can occur when the compressed image or video data are transmitted over an error-prone channel, as typically occurs in wireless communication scenarios. However, for very harsh channels, these tools often do not provide an adequate degree of error protection. In this paper, we propose a novel error-resilience tool for JPEG 2000, based on the concept of ternary arithmetic coders employing a forbidden symbol. Such coders introduce a controlled degree of redundancy during the encoding process, which can be exploited at the decoder side in order to detect and correct errors. We propose a maximum likelihood and a maximum a posteriori context-based decoder, specifically tailored to the JPEG 2000 arithmetic coder, which are able to carry out both hard and soft decoding of a corrupted code-stream. The proposed decoder extends the JPEG 2000 capabilities in error-prone scenarios, without violating the standard syntax. Extensive simulations on video sequences show that the proposed decoders largely outperform the standard in terms of PSNR and visual quality. 相似文献
45.
Bowers Jeffrey S.; Vigliocco Gabriella; Haan Richard 《Canadian Metallurgical Quarterly》1998,24(6):1705
A series of experiments assessed masked priming for letters and words that are visually similar (SIM) and dissimilar (DIS) in upper- and lowercase formats. For letters, robust DIS priming was obtained in a naming task, but this priming did not extend to a variety of non-naming tasks. For words, robust DIS priming was obtained in both naming and non-naming tasks. SIM letter and word priming extended to all tasks, but the effects were generally small for letters. The restricted set of conditions for DIS letter priming suggests that this priming is mediated by phonological-articulatory processes, and the generality of DIS word priming argues that abstract orthographic codes mediate these effects. Consistent with this conclusion, priming between homophones (for both letters and words) was found in a naming task, but little word homophone priming was obtained in a lexical decision task. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
46.
Gabriella del Grosso Anna Gerardi Federico Marchetti 《Mathematics and computers in simulation》1984,26(4):373-376
Some probabilistic techniques are discussed regarding their use in estimating the principal eigenvalue of an elliptic operator. Such estimates are useful when studying models for biochemical reactions governed by lateral diffusion.In this paper we summarize recent results on some mathematical techniques that were developed to study certain biological models. 相似文献
47.
The accuracy of extremely low frequency (ELF) magnetic field measurements can be sensitively varied by the meter probe size when the spatial distribution of the magnetic flux density is highly non-uniform, e.g. if the measurement point is close to the field source. The deviation between measured and actual field varies from point to point depending on the probe dimension and on the source configuration, once the other measurement conditions are fixed. The analysis of this effect is developed through a two-dimensional numerical model that enables the evaluation of the actual field value and of the corresponding probe indication. The error distribution, i.e. the deviation between actual and measured value, is computed for magnetic fields generated by industrial three-phase systems under both balanced and unbalanced supply conditions. The analysis shows how, for a given source, the error depends not simply on the distance from the source in relation to the probe size, but on its spatial distribution, which is complex and cannot be a priori predicted without using a computational tool such as the one proposed. 相似文献
48.
The effect of nerve growth factor (NGF) on ontogenesis of frog mast cells was investigated in vivo by histochemical, morphometric, and ultrastructural analysis. Three groups of tadpoles at various stages of development were used. In the first group, the larvae received i.p. injections of 1 ng NGF/g; the second group received 10 ng NGF/g, while the control group received only the vehicle. The first recognizable mast cells arose symmetrically in the tongue at stage 26 of Witschi's standard table. At stages 26 and 29, the mast cell number in the NGF-injected tadpoles was significantly higher than the control group. From stage 29 onward, the mast cell number rapidly increased in all groups. No significant differences in mast cell number were observed between the control group and the NGF-injected groups at stages 31 and 33. Electron microscopy revealed that at metamorphic climax (stage 33), the mast cells in the NGF-treated groups were more mature than those in the control group. Therefore, nerve growth factor at early stages of tadpole development is likely to induce differentiation of mast cell precursors, while at later stages it is likely to induce maturation of immature mast cells. The close anatomical association between mast cells and perineurium, observed during nerve development, is intriguing. Already in the early stages of nerve development, the mast cells form a network around Schwann cell-axon complexes, together with the perineurial cells. At climax, the mast cells are located between the perineurial layers, suggesting that they may play a role in the tissue-nerve barrier of the perineurium. Nerve growth factor also seems to induce perineurial cell maturation. 相似文献
49.
50.
Mari K. N?ss David J. Young Jianqiang Zhang Jan Erik Olsen Gabriella Tranell 《Oxidation of Metals》2012,78(5-6):363-376
Small scale laboratory experiments on the oxidation of liquid silicon have reproduced important features of the industrial refining of liquid silicon: active oxidation led to the formation of amorphous silica spheres as a reaction product. The boundary condition for active oxidation in terms of maximum oxygen partial pressure in the bulk gas was found to lie between 2·10?3 and 5·10?3?atm at T?=?1,500?°C. The active oxidation of liquid silicon had linear kinetics, and the rate was proportional to bulk oxygen partial pressure and the square root of the linear gas flow rate, consistent with viscous flow mass transfer theory. Classical theory for unconstrained flow over a flat plate led to mass transfer rates for SiO(g) which were 2–3 times slower than observed. However, computational fluid dynamic modeling to take into account the effects of reactor tube walls on flow patterns yielded satisfactory agreement with measured volatilization rates. 相似文献