全文获取类型
收费全文 | 554篇 |
免费 | 30篇 |
专业分类
电工技术 | 12篇 |
综合类 | 1篇 |
化学工业 | 136篇 |
金属工艺 | 8篇 |
机械仪表 | 12篇 |
建筑科学 | 32篇 |
能源动力 | 13篇 |
轻工业 | 54篇 |
水利工程 | 4篇 |
无线电 | 81篇 |
一般工业技术 | 61篇 |
冶金工业 | 42篇 |
原子能技术 | 2篇 |
自动化技术 | 126篇 |
出版年
2023年 | 5篇 |
2022年 | 23篇 |
2021年 | 32篇 |
2020年 | 23篇 |
2019年 | 14篇 |
2018年 | 17篇 |
2017年 | 31篇 |
2016年 | 27篇 |
2015年 | 26篇 |
2014年 | 20篇 |
2013年 | 49篇 |
2012年 | 37篇 |
2011年 | 48篇 |
2010年 | 26篇 |
2009年 | 29篇 |
2008年 | 23篇 |
2007年 | 27篇 |
2006年 | 10篇 |
2005年 | 15篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 16篇 |
1997年 | 12篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有584条查询结果,搜索用时 256 毫秒
521.
The difficulty of introducing hydrogen and fuel cells in the market stems from the fact that they are not an evolutionary innovation such as biofuels or hybrid cars. Instead they create a disruption in technological utilization. The domination of oil technologies sets a socio-economical context favoring actors involved in the current paradigm, and gives less opportunity to alternative fuels to develop and challenge the status quo. If this hypothesis is correct, then companies interested in the hydrogen economy would not become active because of an unstable context or contradictory interests concerning the replacement of the present system. A review of actions and announcements of main actors shows that technology readiness and the absence of infrastructure are the major justifications to delay investments. Some measures are discussed, which could be deployed in order to reduce uncertainties, such as regulation of carbon emissions from cars, technological subvention, and partnerships for infrastructure implementation. 相似文献
522.
Vera Medeiros Nuno Rainha Lisete Paiva Elisabete Lima 《International Journal of Food Properties》2013,16(4):806-817
A new methodology was developed using bromelain as a proteolytic enzyme for the production of a partially hydrolyzed bovine milk formula, without changing the milk's organoleptic and nutritional properties. This study also revealed that the in vitro angiotensin-converting enzyme inhibition increased in the modified milk as compared with the control sample, showing the highest angiotensin-converting enzyme-inhibitory activity for fractions with molecular weights between 3 and 10 kg mol?1. The Lineweaver-Burk plot revealed that the produced milk formula acted as a non-competitive inhibitor, as determined by high performance liquid chromatography. 相似文献
523.
Amélia P. Rauter Catarina Dias Alice Martins Isabel Branco Nuno R. Neng José M. Nogueira Margarida Goulart Filipa V.M. Silva Jorge Justino Clare Trevitt Jon P. Waltho 《Food chemistry》2012
Salvia sclareoides is an aromatic herb native to Portugal, of which phenolic content (Folin–Ciocalteau method), chemical profile (HPLC/DAD), antioxidant activity (DPPH, β-carotene/linoleic acid assays), acute toxicity (MTT method, adapted for non-adherent cells), genotoxicity (short-term chromosomal aberration assay) and prion binding properties were evaluated in the acetone, water, ethanol, methanol and n-butanol extracts. The latter presented the highest phenolic content and antioxidant activity (DPPH assay), and was the single one with the flavonoids (+)-catechin, kaempferol O-glucoside and quercetin. Vanillic acid was the major component of all extracts but gallic, gentisic, caffeic, syringic, coumaric and ferulic acids were also found in some extracts. Only the n-butanol extract had components binding to the cellular form of human prion protein detected by NMR which showed specificity for two regions of the folded domain and for the unstructured N-terminal region. Extracts were not cytotoxic nor genotoxic, reinforcing the potential of S. sclareoides for nutraceutical purposes. 相似文献
524.
Thomas Pellegrini Rui Correia Isabel Trancoso Jorge Baptista Nuno Mamede Maxine Eskenazi 《Computer Speech and Language》2013,27(5):1127-1142
Spoken European Portuguese (EP) is known to be difficult to understand for L2 learners, due to phenomena such as strong vowel reduction. In this paper, we present a method to automatically generate exercises aimed at improving listening comprehension skills in EP. Learners identify the words pronounced in real speech utterances. The exercises introduce two innovative aspects: using broadcast news videos for curriculum and automatically generating exercises with material updated on a daily basis. The videos are automatically transcribed by a speech recognition engine. A filtering chain, used to select appropriate sentences, was validated by a first survey comprised of both manually and automatically selected sentences. Both sets were assigned good to very good subjective quality scores. A second survey concerned the features of the exercise interface. Subjects with varying self-reported exposure to Portuguese as a second language tested several interfaces and functionalities and highlighted their preferred features. The results confirmed that the largest difficulty was the fast speech rate. All participants valued slowed-down audio and video documents, though this feature was more often used by the lowest proficiency subjects. The exercises were integrated into a Web platform where they are automatically updated daily. Though further evaluation is needed to find whether the platform affords skill acquisition, it is expected to be particularly valuable for distance learners who need opportunities to access authentic audio documents in EP. 相似文献
525.
Villegas P.J. Sebastian J. Hernando M. Nuno F. Martinez J.A. 《Power Electronics, IEEE Transactions on》2000,15(5):813-819
The application of the average current mode control (ACMC) to a new type of very efficient post-regulator is studied in this paper. This post-regulator, called series-switching post-regulator (SSR), has been proposed to improve the dynamic response series-switching of power factor correctors (PFC), The post-regulator exhibits very high efficiency due to the fact that only a part of the total power undergoes a power conversion process. Using ACMC, the bandwidth of the post-regulator increases in relation to the one obtained when a conventional voltage-mode control (with or without feedforward) is used. As a result, the attenuation of the input voltage ripple (100-120 Hz) increases and, a lower bulk capacitor can be used to obtain a low voltage ripple at the output, which is extremely important when a battery is connected at the output. This is rather common in distributed power supply systems 相似文献
526.
António Machado Kimberly Kay Jefferson Nuno Cerca 《International journal of molecular sciences》2013,14(6):12004-12012
Certain anaerobic bacterial species tend to predominate the vaginal flora during bacterial vaginosis (BV), with Gardnerella vaginalis being the most common. However, the exact role of G. vaginalis in BV has not yet been determined. The main goal of this study was to test the hypothesis that G. vaginalis is an early colonizer, paving the way for intermediate (e.g., Fusobacterium nucleatum) and late colonizers (e.g., Prevotella bivia). Theoretically, in order to function as an early colonizer, species would need to be able to adhere to vaginal epithelium, even in the presence of vaginal lactobacilli. Therefore, we quantified adherence of G. vaginalis and other BV-associated bacteria to an inert surface pre-coated with Lactobacillus crispatus using a new Peptide Nucleic Acid (PNA) Fluorescence In Situ Hybridization (FISH) methodology. We found that G. vaginalis had the greatest capacity to adhere in the presence of L. crispatus. Theoretically, an early colonizer would contribute to the adherence and/or growth of additional species, so we next quantified the effect of G. vaginalis biofilms on the adherence and growth of other BV-associated species by quantitative Polymerase Chain Reaction (qPCR) technique. Interestingly, G. vaginalis derived a growth benefit from the addition of a second species, regardless of the species. Conversely, G. vaginalis biofilms enhanced the growth of P. bivia, and to a minor extent of F. nucleatum. These results contribute to our understanding of BV biofilm formation and the progression of the disorder. 相似文献
527.
A numerical scheme to obtain radar cross section (RCS) of three-dimensional bodies of resonant size (BRS) with arbitrary geometry and material composition is described. The RCS is obtained by solving the electric-field integral equation (EFIE) using the conjugate gradient-fast Fourier transform method (CG-FFT). The choice of a suitable set of basis and testing functions to discretize the EFIE leads to a very accurate and computationaly efficient CG-FFT procedure. This accuracy is checked by comparison with RCS measurements or predictions by other methods. As compared to the moment method, this CG-FFT scheme avoids the storage of large matrices and reduces the computer time by orders of magnitude 相似文献
528.
Wedding B. Koffers K. Franz B. Mathoorasing D. Kazmierski C. Pereira Monteiro P. Nuno Matos J. 《Electronics letters》1995,31(7):566-568
The optical transmission of 20 Gbit/s signals over a record distance of 53 km standard nondispersion-shifted singlemode fibre (SMF) without optical dispersion compensation has been demonstrated successfully using a directly modulated MQW DFB laser operating at 1544 nm 相似文献
529.
Mario Prats David Ribas Narcís Palomeras Juan Carlos García Volker Nannen Stephan Wirth José Javier Fernández Joan P. Beltrán Ricard Campos Pere Ridao Pedro J. Sanz Gabriel Oliver Marc Carreras Nuno Gracias Raúl Marín Alberto Ortiz 《Intelligent Service Robotics》2012,5(1):19-31
Starting in January 2009, the RAUVI (Reconfigurable Autonomous Underwater Vehicle for Intervention Missions) project is a 3-year coordinated research action funded by the Spanish Ministry of Research and Innovation. In this paper, the state of progress after 2?years of continuous research is reported. As a first experimental validation of the complete system, a search and recovery problem is addressed, consisting of finding and recovering a flight data recorder placed at an unknown position at the bottom of a water tank. An overview of the techniques used to successfully solve the problem in an autonomous way is provided. The obtained results are very promising and are the first step toward the final test in shallow water at the end of 2011. 相似文献
530.
Tsjerk A. Wassenaar Marc van Dijk Nuno Loureiro-Ferreira Gijs van der Schot Sjoerd J. de Vries Christophe Schmitz Johan van der Zwan Rolf Boelens Andrea Giachetti Lucio Ferella Antonio Rosato Ivano Bertini Torsten Herrmann Hendrik R. A. Jonker Anurag Bagaria Victor Jaravine Peter G��ntert Harald Schwalbe Wim F. Vranken Jurgen F. Doreleijers Gert Vriend Geerten W. Vuister Daniel Franke Alexey Kikhney Dmitri I. Svergun Rasmus H. Fogh John Ionides Ernest D. Laue Chris Spronk Simonas Jurk?a Marco Verlato Simone Badoer Stefano Dal Pra Mirco Mazzucato Eric Frizziero Alexandre M. J. J. Bonvin 《Journal of Grid Computing》2012,10(4):743-767
The WeNMR (http://www.wenmr.eu) project is a European Union funded international effort to streamline and automate analysis of Nuclear Magnetic Resonance (NMR) and Small Angle X-Ray scattering (SAXS) imaging data for atomic and near-atomic resolution molecular structures. Conventional calculation of structure requires the use of various software packages, considerable user expertise and ample computational resources. To facilitate the use of NMR spectroscopy and SAXS in life sciences the WeNMR consortium has established standard computational workflows and services through easy-to-use web interfaces, while still retaining sufficient flexibility to handle more specific requests. Thus far, a number of programs often used in structural biology have been made available through application portals. The implementation of these services, in particular the distribution of calculations to a Grid computing infrastructure, involves a novel mechanism for submission and handling of jobs that is independent of the type of job being run. With over 450 registered users (September 2012), WeNMR is currently the largest Virtual Organization (VO) in life sciences. With its large and worldwide user community, WeNMR has become the first Virtual Research Community officially recognized by the European Grid Infrastructure (EGI). 相似文献