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91.
A highly sensitive edge detector has been developed that uses tissue classification of pixels based on analysis of data in their local neighborhoods. In conjunction with recursive region growing, it has been used successfully to define regions of interest (ROI) when applied specifically to gradient echo MR images of the heart. The detector adapts to nonuniformity by carrying out an independent analysis at each location. If two tissues are present in a neighborhood and the pixel at that location cannot be classified with the seed pixel, a region edge has been crossed and recursion is stopped. No geometric assumptions relating to object shape such as definition of a region center and radial search are required. The detector was applied to multi-slice, multi-phase images of the heart from 26 subjects. A segmentation strategy specified slice processing order, graded ROIs, and used successfully detected ROIs to guide subsequent detection. Segmentation of all images resulted in a 90.3% median edge pixel detection efficiency. 相似文献
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Ian Singleton 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1994,59(1):9-23
The ability of microorganisms to metabolise xenobiotic compounds has received much attention due to the environmental persistence and toxicity of these chemicals. The microbial degradation of xenobiotics is seen as a cost effective method of removing these pollutants from the environment by a process now known as bioremediation. Microbial treatment of industrial effluents is also possible. Fundamental work has revealed that a wide variety of microorganisms are capable of degrading an equally wide range of organic pollutants. Pure and mixed cultures of microorganisms have been studied and degradation is observed under both aerobic and anaerobic conditions. Breakdown products have been found during work on the degradative pathways involved and toxicological assessments using bacteria and higher organisms (fish, plants) have been used to determine the toxicity of these intermediates. Many of the degradative genes responsible for xenobiotic metabolism are present on plasmids, transposons or are grouped in clusters on chromosomes. This provides clues to the evolution of degradative pathways and makes the task of genetic manipulation easier such that new microbial strains capable of efficiently degrading pollutants can be developed. Several enzymes involved in xenobiotic metabolism have been isolated and factors affecting their activity investigated. Genetically manipulated strains or naturally isolated organisms may be used in the treatment of industrial wastes or as inocula to enhance degradation in the environment. Environmental factors, including pH, temperature, bioavailability, nutrient supply and oxygen availability have been shown to affect xenobiotic biodegradation. These factors must be optimised to obtain a satisfactory microbial treatment process. Using information gained from fundamental research, bioremediation technology has been used to detoxify different contaminated environments and the results of field studies are very encouraging. 相似文献
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Stripe and chequerboard phases appear in many metal oxide compounds, and are thought to be linked to exotic behaviour such as high-temperature superconductivity and colossal magnetoresistance. It is therefore extremely important to understand the fundamental nature of such phases. The so-called stripe phase of the manganites has long been interpreted as the localization of charge at atomic sites. Here, we present resistance measurements on La(0.50)Ca(0.50)MnO(3) that strongly suggest that this state is in fact a prototypical charge-density wave (CDW) that undergoes collective transport. Dramatic resistance hysteresis effects and broadband noise properties are observed, both of which are typical of sliding CDW systems. Moreover, the high levels of disorder typical of manganites result in behaviour similar to that of well-known disordered CDW materials. The CDW-type behaviour of the manganite superstructure suggests that unusual transport and structural properties do not require exotic physics, but could emerge when a well-understood phase (the CDW) coexists with disorder. 相似文献
96.
Morphology of the nonspherically decaying radiation beam generated by a rotating superluminal source
Ardavan H Ardavan A Singleton J Fasel J Schmidt A 《Journal of the Optical Society of America. A, Optics, image science, and vision》2007,24(8):2443-2456
We consider the nonspherically decaying radiation field that is generated by a polarization current with a superluminally rotating distribution pattern in vacuum, a field that decays with the distance R(P) from its source as R(P)(-1/2), instead of R(P)(-1). It is shown (i) that the nonspherical decay of this emission remains in force at all distances from its source independently of the frequency of the radiation, (ii) that the part of the source that makes the main contribution toward the value of the nonspherically decaying field has a filamentary structure whose radial and azimuthal widths become narrower (as R(P)(-2) and R(P)(-3), respectively) the farther the observer is from the source, (iii) that the loci on which the waves emanating from this filament interfere constructively delineate a radiation subbeam that is nondiffracting in the polar direction, (iv) that the cross-sectional area of each nondiffracting subbeam increases as R(P), instead of R(P)(2), so that the requirements of conservation of energy are met by the nonspherically decaying radiation automatically, and (v) that the overall radiation beam within which the field decays nonspherically consists, in general, of the incoherent superposition of such coherent nondiffracting subbeams. These findings are related to the recent construction and use of superluminal sources in the laboratory and numerical models of the emission from them. We also briefly discuss the relevance of these results to the giant pulses received from pulsars. 相似文献
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P. J. Van der Wel S. M. Hayden M. Springford P. Meeson J. Caulfield J. Singleton W. Hayes M. Kurmoo P. Day 《Synthetic Metals》1995,70(1-3):831-832
We report a study of the de Haas-van Alphen effect near the upper critical field in the organic superconductor κ-(ET)2Cu(NCS)2. The experiments have been carried out for a range of sample orientations with respect to the magnetic field and of temperatures down to 20 mK. On entering the vortex state, an attenuation of the dHvA signal is observed relative to an extrapolation of the standard Lifshitz-Kosevich formula using band parameters measured in the normal state. 相似文献