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51.
A liquid-crystal optical phased-array technology that uses stressed liquid crystals provides a new type of tip-tilt wavefront corrector. It demonstrates a very fast time response (10 kHz) and high beam-steering efficiency (approximately 91%). The new technology presented here will allow for a nonmechanical, high-speed correction with simple device construction. 相似文献
52.
When studying the degree of overall agreement between the nominal responses of two raters, it is customary to use the coefficient kappa. A more detailed analysis requires the evaluation of the degree of agreement category by category, and this is carried out in two different ways: using the value of kappa in the collapsed table for each category or using the agreement index for each category (proportion of agreements observed). Both indices have disadvantages: the former is sensitive to marginal totals; the latter is not chance corrected; and neither distinguishes the case where one of the two raters is a gold standard (an expert) from the case where neither rater is a gold standard. This article suggests five chance-corrected indices which are not sensitive to marginal totals and which differ depending on whether there is a standard rater. The article also justifies the reason for poor performance of kappa when the two marginal totals are unbalanced (especially if they are so in opposite directions) and the reason for its good performance when analysing the various 2 x 2 tables obtained by the collapse of a wider table. 相似文献
53.
The theoretical framework for the computation of electromagnetic fields and electron optical phase-shifts in Fourier space has been recently applied to objects with long-range fringing fields, such as reverse-biased p-n junctions and magnetic stripe domains near a specimen edge. In addition to new analytical results, in this work, we present a critical comparison between numerical and analytical computations. The influence of explicit and implicit boundary conditions on the phase shifts and phase-contrast images is also investigated in detail. 相似文献
54.
Microwave radiometer blackbody calibration standard for use at millimeter wavelengths 总被引:1,自引:0,他引:1
We describe a high-temperature reference load designed for calibration of microwave radiometers at frequencies of 80-150 GHz. An effective temperature of 410 K and a power reflection coefficient of less than 5 x 10(-4) have been measured at frequencies between 85 and 95 GHz. 相似文献
56.
Knapp PF Greenly JB Gourdain PA Hoyt CL Pikuz SA Shelkovenko TA Hammer DA 《The Review of scientific instruments》2010,81(10):10E501
Monochromatic x-ray backlighting has been employed with great success for imaging of plasmas with strong self-emission such as x-pinches and wire array z-pinches. However, implementation of a monochromatic backlighting system typically requires extremely high quality spherically bent crystals which are difficult to manufacture and can be prohibitively expensive. Furthermore, the crystal must have a direct line of sight to the object, which typically emits copious amounts of radiation and debris. We present a quasimonochromatic x-ray backlighting system which employs an elliptically bent mica crystal as the dispersive element. In this scheme a narrow band of continuum radiation is selected for imaging, instead of line radiation in the case of monochromatic imaging. The flat piece of mica is bent using a simple four-point bending apparatus that allows the curvature of the crystal to be adjusted in situ for imaging in the desired wavelength band. This system has the advantage that it is very cost effective, has a large aperture, and is extremely flexible. The principles of operation of the system are discussed and its performance is analyzed. 相似文献
57.
Teunis PF Xu M Fleming KK Yang J Moe CL Lechevallier MW 《Environmental science & technology》2010,44(22):8561-8566
Contaminants from the soil surrounding drinking water distribution systems are thought to not enter the drinking water when sufficient internal pressure is maintained. Pressure transients may cause short intervals of negative pressure, and the soil near drinking water pipes often contains fecal material due to the proximity of sewage lines, so that a pressure event may cause intrusion of pathogens. This paper presents a risk model for predicting intrusion and dilution of viruses and their transport to consumers. Random entry and dilution of virus was simulated by embedding the hydraulic model into a Monte Carlo simulation. Special attention was given to adjusting for the coincidence of virus presence and use of tap water, as independently occurring short-term events within the longer interval that the virus is predicted to travel in any branch of the distribution system. The probability that a consumer drinks water contaminated with virus is small, but when this happens the virus concentration tends to be high and the risk of infection may be considerable. The spatial distribution of infection risk is highly heterogeneous. The presence of a chlorine residual reduces the infection risk. 相似文献
58.
Segmentation of the left ventricle of the heart in 3-D+t MRI data using an optimized nonrigid temporal model 总被引:1,自引:0,他引:1
Modern medical imaging modalities provide large amounts of information in both the spatial and temporal domains and the incorporation of this information in a coherent algorithmic framework is a significant challenge. In this paper, we present a novel and intuitive approach to combine 3-D spatial and temporal (3-D + time) magnetic resonance imaging (MRI) data in an integrated segmentation algorithm to extract the myocardium of the left ventricle. A novel level-set segmentation process is developed that simultaneously delineates and tracks the boundaries of the left ventricle muscle. By encoding prior knowledge about cardiac temporal evolution in a parametric framework, an expectation-maximization algorithm optimally tracks the myocardial deformation over the cardiac cycle. The expectation step deforms the level-set function while the maximization step updates the prior temporal model parameters to perform the segmentation in a nonrigid sense. 相似文献
59.
Arunachalam K Maccarini PF Stauffer PR 《IEEE transactions on bio-medical engineering》2008,55(10):2397-2406
60.
Docherty KS Stone EA Ulbrich IM DeCarlo PF Snyder DC Schauer JJ Peltier RE Weber RJ Murphy SM Seinfeld JH Grover BD Eatough DJ Jimenez JL 《Environmental science & technology》2008,42(20):7655-7662
Ambient sampling was conducted in Riverside, California during the 2005 Study of Organic Aerosols in Riverside to characterize the composition and sources of organic aerosol using a variety of state-of-the-art instrumentation and source apportionmenttechniques. The secondary organic aerosol (SOA) mass is estimated by elemental carbon and carbon monoxide tracer methods, water soluble organic carbon content, chemical mass balance of organic molecular markers, and positive matrix factorization of high-resolution aerosol mass spectrometer data. Estimates obtained from each ofthese methods indicate that the organic fraction in ambient aerosol is overwhelmingly secondary in nature during a period of several weeks with moderate ozone concentrations and that SOA is the single largest component of PM1 aerosol in Riverside. Average SOA/OA contributions of 70-90% were observed during midday periods, whereas minimum SOA contributions of approximately 45% were observed during peak morning traffic periods. These results are contraryto previous estimates of SOAthroughout the Los Angeles Basin which reported that, other than during severe photochemical smog episodes, SOA was lower than primary OA. Possible reasons for these differences are discussed. 相似文献