全文获取类型
收费全文 | 6269篇 |
免费 | 429篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 38篇 |
综合类 | 3篇 |
化学工业 | 1230篇 |
金属工艺 | 81篇 |
机械仪表 | 114篇 |
建筑科学 | 188篇 |
矿业工程 | 9篇 |
能源动力 | 145篇 |
轻工业 | 1371篇 |
水利工程 | 87篇 |
石油天然气 | 29篇 |
无线电 | 285篇 |
一般工业技术 | 905篇 |
冶金工业 | 1263篇 |
原子能技术 | 13篇 |
自动化技术 | 939篇 |
出版年
2024年 | 16篇 |
2023年 | 58篇 |
2022年 | 85篇 |
2021年 | 160篇 |
2020年 | 146篇 |
2019年 | 153篇 |
2018年 | 266篇 |
2017年 | 255篇 |
2016年 | 237篇 |
2015年 | 200篇 |
2014年 | 246篇 |
2013年 | 497篇 |
2012年 | 425篇 |
2011年 | 418篇 |
2010年 | 322篇 |
2009年 | 283篇 |
2008年 | 307篇 |
2007年 | 286篇 |
2006年 | 188篇 |
2005年 | 153篇 |
2004年 | 126篇 |
2003年 | 116篇 |
2002年 | 106篇 |
2001年 | 89篇 |
2000年 | 58篇 |
1999年 | 75篇 |
1998年 | 521篇 |
1997年 | 280篇 |
1996年 | 182篇 |
1995年 | 96篇 |
1994年 | 78篇 |
1993年 | 73篇 |
1992年 | 21篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 18篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 19篇 |
1973年 | 3篇 |
排序方式: 共有6700条查询结果,搜索用时 15 毫秒
21.
22.
E Talavera G Martínez-Lorenzana G Corkidi M Léon-Olea M Condés-Lara 《Canadian Metallurgical Quarterly》1997,1(6):484-493
The aim of this study was to determine the neuronal participation of nitric oxide (NO) in experimental epilepsy. To reach this objective, we established the amount of cells presenting nitric oxide synthase (NOS) and the amygdaline concentrations in the L-arginine-nitric oxide synthesis pathway. A group of fully epileptic rats, induced by the kindling procedure and that had reached at least 10 generalized seizures, was studied. We evaluated behavioral stages, electroencephalographic activities, and histochemical NOS-positive cells and carried out high-pressure liquid chromatography (HPLC) determinations of arginine, citrulline, and glutamic acid. Our results showed that behavioral and electrographic frequency, and duration of epileptic activities, were increased during the kindling process. Image processing system of NOS cells showed two types of intensities in cell stains in hippocampus, caudate-putamen, and amygdala. When we independently counted the two types of NOS stain cells, a selective increase in the number and density of weak-stained cells was observed, while dark-stained cells did not change in the studied structures. Additionally, arginine, citrulline, and glutamic acid concentrations in amygdala increased in kindled animals. The differential and specific increase in the stained cells expressing the nitric oxide synthase, as well as the increase in concentrations of the L-arginine-nitric oxide pathway in amygdala, suggested a relationship with the progressive augmentation in the electrophysiological hyperactivity characteristic of generalized epilepsy. 相似文献
23.
Marcos Craizer Thomas Lewiner Jean-Marie Morvan 《Journal of Mathematical Imaging and Vision》2007,29(2-3):131-140
Image and geometry processing applications estimate the local geometry of objects using information localized at points. They usually consider information about the tangents as a side product of the points coordinates. This work proposes parabolic polygons as a model for discrete curves, which intrinsically combines points and tangents. This model is naturally affine invariant, which makes it particularly adapted to computer vision applications. As a direct application of this affine invariance, this paper introduces an affine curvature estimator that has a great potential to improve computer vision tasks such as matching and registering. As a proof-of-concept, this work also proposes an affine invariant curve reconstruction from point and tangent data. 相似文献
24.
Commercial anatase containing an appreciable amount of sulphur has been treated for sulphur removal by calcination at increasing temperatures or soaking with aqueous NaOH solutions. It has been found that both methods are active for sulphur removal, but the first one also leads to a sharp sintering of the titania particles. On the other hand, treatment with NaOHaq leads to incorporation of sodium cations. Both treatments lead also to changes in surface acidity, as measured by Fourier transform infrared (FT-IR) monitoring of pyridine adsorption. 相似文献
25.
We describe a patient with aspergillosis of the maxillary antrum, and systemic affectation (anemia, anorexia, fever). Through a Caldwell-Luck approach, the maxillary antrum was opened and an irregular mass removed, postoperatively the patient has done well, disappearing in two months the ORL and systemic symptoms. 相似文献
26.
Vicente Rodríguez Montequín Francisco Ortega Fernández Nicolás Abajo de Martínez Juan Antonio González Rodríguez 《JOM Journal of the Minerals, Metals and Materials Society》2002,54(7):46-50
This research summary discusses the application of neural networks, evolutionary strategies, and other artificial intelligence
techniques in the modeling and optimization of the models used for temperature, rolling force, and torque calculation in heavy
plate milling. 相似文献
27.
F Javier Álvarez‐Hornos Carmen Gabaldón Vicente Martínez‐Soria Paula Marzal Josep‐Manuel Penya‐roja 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):643-653
BACKGROUND: Two peat biofilters were used for the removal of toluene from air for one year. One biofilter was fed with pure toluene and the other received 1:1 (by weight) ethyl acetate:toluene mixture. RESULTS: The biofilters were operated under continuous loading: the toluene inlet load (IL) at which 80% removal occurred was 116 g m?3 h?1 at 57 s gas residence time. Maximum elimination capacity of 360 g m?3 h?1 was obtained at an IL of 745 g m?3 h?1. The elimination of toluene was inhibited by the presence of ethyl acetate. Intermittent loading, with pollutants supplied for 16 h/day, 5 days/week, did not significantly affect the removal efficiency (RE). Biomass was fully activated in 2 h after night closures, but 6 h were required to recover RE after weekend closures. Live cell density remained relatively constant over the operational period, while the dead cell fraction increased. Finally, a 15 day starvation period was applied and operation then re‐started. Performance was restored with similar re‐acclimatization period to that after weekend closures, and a reduction in dead cell fraction was observed. CONCLUSION: This study demonstrates the capacity of the system to handle intermittent loading conditions that are common in industrial practices, including long‐term starvation. Copyright © 2008 Society of Chemical Industry 相似文献
28.
In this work, we investigate the linear viscoelastic response of high molecular weight ethylene/1‐hexene copolymers, characterized by a narrow molecular weight distribution and comonomer content in the range from 0 to 10 mol %. A variation in the entanglement plateau modulus has been found in agreement with the recently developed packing length model. The packing model applied to viscoelastic data suggests decreased values of the characteristic ratio, accordingly with recent computer simulation results. The flow activation energy increases as the side chain content increases. This feature is thought to be related to the mobility of the molecules. The presence of side branches due to the comonomer hinders the mobility of the molecules, and increases the thermal barrier for the segmental motion. Then in the comonomer content range studied, the increase of the flow activation energy goes parallel with a decrease in the characteristic ratio. This result suggests that more parameters than only the stiffness of the chain modulate the thermal dependence of viscoelastic properties. A more refined study is necessary combining experiments with computer simulations in order to elucidate these aspects. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
29.
Peculiarities of the material composition and physicomechanical characteristics of specific swelling soils are discussed.
The authors studied processes of swelling and shrinking and quantitative changes in the soils' properties as a result of these
processes in laboratory and field conditions.
Dnepropetrovsk Construction Engineering Institute. Translated from Osnovaniya. Fundamenty i Mekhanika Gruntov, No. 2, pp.
24–26, March–April, 1994. 相似文献
30.
Different intravascular ultrasound (IVUS) systems vary in their image presentation. The purpose of this study was to compare four IVUS systems in vitro to determine the accuracy of tissue characterization of atherosclerotic plaque compared with histology. Ninety-eight plaque segments from 23 formalin-fixed human iliac arteries were imaged in saline at room temperature with four different IVUS systems. To assess the accuracy of IVUS in describing plaque, three types of analysis were performed: (1) the ability to identify the presence and extent of lumen or plaque boundary; (2) sensitivity, specificity, and interobserver variability of IVUS in qualitatively identifying plaque components compared with histology; and (3) quantification of calcification. The synthetic aperture device had a lower sensitivity in identifying lumen and plaque boundaries (87%, 38% respectively) compared with other machines (96%-100%, 95%-100%). All three mechanically rotating systems had fair to good sensitivities for identifying calcification (57%-73%) or lipid filled areas (50%-83%). The sensitivity of discriminating fibrous tissue from fatty areas was low (39%-52%). The synthetic aperture system had a significantly lower sensitivity for identifying all three tissue types (4%-21%). There was significant interobserver variability (kappa value = 0.47-0.68) as well as machine to machine variability (kappa value = 0.52) for tissue characterization. Calcified areas were underestimated by System 1 (p < .05) and System 4 (p < .01) because of weaker echo reflections or poor image quality. There are significant differences in image representation among these four IVUS systems in the diagnosis of tissue components of complex atherosclerotic plaque. These variabilities should be considered when interpreting studies performed with different machines. 相似文献