首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   788篇
  免费   4篇
电工技术   7篇
综合类   1篇
化学工业   86篇
金属工艺   5篇
机械仪表   15篇
建筑科学   70篇
矿业工程   3篇
能源动力   20篇
轻工业   85篇
水利工程   9篇
石油天然气   5篇
无线电   53篇
一般工业技术   113篇
冶金工业   233篇
原子能技术   3篇
自动化技术   84篇
  2023年   9篇
  2022年   5篇
  2021年   8篇
  2020年   11篇
  2019年   11篇
  2018年   7篇
  2017年   9篇
  2016年   15篇
  2015年   8篇
  2014年   14篇
  2013年   23篇
  2012年   22篇
  2011年   35篇
  2010年   23篇
  2009年   23篇
  2008年   27篇
  2007年   35篇
  2006年   27篇
  2005年   23篇
  2004年   19篇
  2003年   22篇
  2002年   13篇
  2001年   19篇
  2000年   15篇
  1999年   25篇
  1998年   64篇
  1997年   40篇
  1996年   22篇
  1995年   16篇
  1994年   12篇
  1993年   21篇
  1992年   16篇
  1991年   12篇
  1990年   10篇
  1989年   10篇
  1988年   9篇
  1987年   7篇
  1986年   9篇
  1985年   10篇
  1984年   5篇
  1983年   4篇
  1982年   6篇
  1981年   11篇
  1980年   5篇
  1978年   5篇
  1977年   8篇
  1976年   8篇
  1975年   7篇
  1973年   6篇
  1970年   3篇
排序方式: 共有792条查询结果,搜索用时 15 毫秒
771.
A high-speed motion analysis technique for measuring shocks in cushioned drops is developed and compared with the conventional accelerometer method. Actual drop-test results show significant differences between the measured peak decelerations using the two methods. The drop-test results are also compared with the published cushion-curve data and are again found to be in disagreement. The errors associated with each method are discussed and related back to the observed differences in measured acceleration.  相似文献   
772.
ZrO2 nanocrystals were synthesised by a microwave-assisted hydrothermal method using zirconium oxychloride (ZrOCl2·8H2O), yttrium chloride (YCl3·6H2O), and liquor ammonia (NH3·H2O) as raw materials, triethanolamine (TEOA) as mineraliser, and polyethylene glycol (PEG) as dispersant. The obtained products were characterised with thermogravimetry-differential scanning calorimetry (TG-DSC), Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that the concentration of ZrOCl2·8H2O had little effect on the material properties, whereas the PEG molecular weight, microwave hydrothermal time and temperature, and the concentration of TEOA greatly influenced the dispersibility of the nano-sized zirconia powders. XRD and FT-IR analyses indicated that the ZrO2 nanocrystals synthesised by the microwave hydrothermal method had a tetragonal phase without any trace of monoclinic or cubic phases. The optimal parameters for preparing nano-zirconia powders with appreciable crystallinity and crystal forms included the use of PEG1000/PEG2000/PEG4000 dispersants, a microwave hydrothermal time of 30–50 min and a temperature of 200–240 °C, and a TEOA concentration of 0.3–0.5 M. Nano-ZrO2 powder prepared via our optimised microwave hydrothermal method contained mostly tetrahedral, spherically shaped, highly homogeneous, and well-dispersed 20–30 nm particles.  相似文献   
773.
The quality of medical images must be quantified with reference to specific diagnostic tasks. Image quality is limited by fundamental physics, engineering limitations, radiation safety concerns, and imaging time constraints (among other things). There is now a gold standard for assessing human visual decision performance: the ideal Bayesian observer. Unfortunately, there are no mathematical tools to use this gold standard for realistically complex tasks. As an alternative, one can use the optimum linear discriminator (Fisher-Hotelling) model as a silver standard while en route to clinical realism. The goal of scientists working in the area is to develop mathematical models of human observers that will help equipment designers to optimize design trade-offs for specific diagnostic tasks. The current strategy is to modify the Fisher-Hotelling model to include certain limitations of the human observer visual system. The model must be both robust enough and mathematically tractable enough to be used to predict performance for clinical classification and estimation tasks. Statistical models also must be developed that describe realistic signals (lesions and abnormalities) and the normal patient structure that is the background in which these signals must be detected or identified.  相似文献   
774.
The United Kingdom is within the geographical area in which Aedes albopictus could survive. A large number of used car tyres are imported and a number of introduced cases of dengue fever occur annually. The health authorities should be aware of the possibility of dengue transmission.  相似文献   
775.
We derive expressions for the intensity-intensity correlations of a field produced on scattering of a random field governed by Gaussian statistics from a particle with a deterministic or a random refractive index distribution. Our results generalize the ones in [Opt. Lett. 35, 4000, 2010] to the case of an arbitrarily correlated incident field. We consider as specific examples the cases of a single plane wave and two partially correlated plane waves incident upon the scatterer.  相似文献   
776.
Reports an error in "Personality and risk for Alzheimer's disease in adults 72 years of age and older: A 6-year follow-up" by Paul R. Duberstein, Benjamin P. Chapman, Hilary A. Tindle, Kaycee M. Sink, Patricia Bamonti, John Robbins, Anthony F. Jerant and Peter Franks (Psychology and Aging, , , np). This article contains an error in the Discussion, under the Implications, Caveats, Future Directions heading. The third paragraph includes sentences that should have been removed, as they are a variation on similar text immediately following. The sentences that should have been removed are presented in the erratum. (The following abstract of the original article appeared in record 2010-22067-001.) We conducted secondary analyses to determine the relationship between longstanding personality traits and risk for Alzheimer's disease (AD) among 767 participants 72 years of age or older who were followed for more than 6 years. Personality was assessed with the NEO-FFI. We hypothesized that elevated Neuroticism, lower Openness, and lower Conscientiousness would be independently associated with risk of AD. Hypotheses were supported. The finding that AD risk is associated with elevated Neuroticism and lower Conscientiousness can be added to the accumulating literature documenting the pathogenic effects of these two traits. The link between lower Openness and AD risk is consistent with recent findings on cognitive activity and AD risk. Findings have implications for prevention research and for the conceptualization of the etiology of AD. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
777.
As part of a generation of architects graduating after the 2008 global financial crisis, Arthur Mamou-Mani and Toby Burgess developed an ethos of digital self-sufficiency. This is one that they have passed on to their students in Diploma Studio 10 at the University of Westminster, teaching them to self-build using digital fabrication techniques, but also to fund their work through crowdfunding, while promoting it on social media.  相似文献   
778.
Environmental risk assessment of nanomaterials requires information not only on their toxicity to non-target organisms, but also on their potential exposure pathways. Here we report on the transport and fate of quantum dots (QDs) in the total environment: from soils, through their uptake into plants, to their passage through insects following ingestion. Our QDs are nanoparticles with an average particle size of 6.5 nm. Breakthrough curves obtained with CdTe/mercaptopropionic acid QDs applied to columns of top soil from a New Zealand organic apple orchard, a Hastings silt loam, showed there to be preferential flow through the soil's macropores. Yet the effluent recovery of QDs was just 60%, even after several pore volumes, indicating that about 40% of the influent QDs were filtered and retained by the soil column via some unknown exchange/adsorption/sequestration mechanism. Glycine-, mercaptosuccinic acid-, cysteine-, and amine-conjugated CdSe/ZnS QDs were visibly transported to a limited extent in the vasculature of ryegrass (Lolium perenne), onion (Allium cepa) and chrysanthemum (Chrysanthemum sp.) plants when cut stems were placed in aqueous QD solutions. However, they were not seen to be taken up at all by rooted whole plants of ryegrass, onion, or Arabidopsis thaliana placed in these solutions. Leafroller (Lepidoptera: Tortricidae) larvae fed with these QDs for two or four days, showed fluorescence along the entire gut, in their frass (larval feces), and, at a lower intensity, in their haemolymph. Fluorescent QDs were also observed and elevated cadmium levels detected inside the bodies of adult moths that had been fed QDs as larvae. These results suggest that exposure scenarios for QDs in the total environment could be quite complex and variable in each environmental domain.  相似文献   
779.
Fiber tracking in diffusion tensor magnetic resonance images (DTIs) reveals 3-D structural connectivity of the brain conveniently and thus is a viable tool for investigating neural differences. Unfortunately, local noise, image artifacts and numerical tracking errors during integration-based techniques are cumulative. Prematurely terminated fibers and under-sampled fiber bundles result in incomplete reconstruction of white matter fiber tracts and hence incorrect anatomical measurements. Quantitative cross-subject tract analysis, which is critical for abnormality detection, is complicated by inefficient and inaccurate tract reconstruction and normalization from fiber bundles. Because of the above problems, we propose a parcellation method that aims for lower sensitivity to initialization and local orientation error by directly segmenting full white matter tracts (Fasciculography), rather than reconstructing individual curves, from diffusion tensor fields. A fast, robust volumetric, and intrinsically normalized solution is achieved by noise-filtering using a generic parametrized tract model to prevent premature tract termination. At the same time, orientation information reduces the search space, significantly speeding up the tract parcellation process with less human intervention. Detailed comparisons against streamline tracking, shortest-path tracking, and nonrigid registration using synthetic and real DTIs confirmed the superior properties of Fasciculography. Since a normalized tract can be delineated interactively in a just few seconds using the proposed method, accurate high volume tract comparisons become feasible.  相似文献   
780.
Oxygen transport in amorphous poly(ethylene furanoate) (PEF) was studied at various temperatures using complementary permeation and pressure-decay sorption techniques. A significant reduction in oxygen permeability of ∼11× was observed at 35 °C for PEF compared to poly(ethylene terephthalate) (PET), and is attributed primarily to reduction in chain segment mobility for PEF resulting from a hindrance of furan ring flipping. A custom-built high accuracy sorption system allowed determination of temperature-dependent so-called dual-mode parameters that have not been reported for oxygen in any polyester. Energetic parameters, i.e. the enthalpy of sorption and activation energies of diffusion and permeation, were measured for oxygen in PEF and discussed in the context of PET and related polyesters. The current work presents the first detailed study of penetrant transport in PEF, which demonstrates the impressive performance enhancements of PEF compared to PET.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号