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81.
We measure with a gated intensified CCD camera the cross-polarized backscattered light from a linearly polarized laser beam penetrating a cloud made of spherical particles. In accordance with previously published results we observe a clear azimuthal pattern in the recorded images. We show that the pattern is symmetrical, that it originates from second-order scattering, and that higher-order scattering causes blurring that increases with optical depth. We also find that the contrast in the symmetrical features can be related to measurement of the optical depth. Moreover, when the blurring contributions are identified and subtracted, the resulting pattern provides a pure second-order scattering measurement that can be used for retrieval of droplet size. 相似文献
82.
An experimental method is presented for characterization of the combined intensity and frequency modulation produced when the injection current of a laser diode is modulated. The reported technique is based on the analysis of the harmonic signals produced when a modulated laser is used to probe a gas absorption line by the so-called wavelength-modulation spectroscopy method. Based on a theoretical model of this technique, we present two methods that facilitate the determination of (i) the deviation in laser frequency and (ii) the phase shift between intensity and frequency modulation. These methods are illustrated experimentally by measurement of the modulation parameters of a 2-microm distributed-feedback laser by use of a CO2 absorption line. The experimental results have been compared with those obtained with another traditional method and have shown full agreement in the frequency range (400 Hz-30 kHz) considered. 相似文献
83.
Sarantinopoulos P Makras L Vaningelgem F Kalantzopoulos G De Vuyst L Tsakalidou E 《International journal of food microbiology》2003,84(2):197-206
Citrate metabolism by Enterococcus faecium FAIR-E 198, isolated from Greek Feta cheese, was studied in various growth media containing citrate either in the presence of glucose, or as the sole carbon source, both under aerobic and anaerobic conditions. In de Man-Rogosa-Sharpe (MRS) broth with increasing citrate concentrations, cometabolism of citrate and glucose took place. Glucose was stoichiometrically converted into lactate, while citrate into acetate. Glucose consumption and biomass yield were enhanced with increasing initial citrate concentrations, even though maximum specific growth rate was not. When citrate was used as the sole carbon source in increasing initial concentrations, the main end product was acetate. Small amounts of lactate, formate, ethanol, and acetoin were also produced. In all cases, no significant differences were observed between aerobic and anaerobic conditions. However, when citrate was used as sole carbon source, formate production was favored in the absence of oxygen. The present work shows that E. faecium is able to utilize citrate in synthetic media, either in the presence of glucose or as the sole carbon source, resulting in energy production and the formation of aroma compounds. 相似文献
84.
Compound-specific carbon isotope analysis of volatile organic compounds in the low-microgram per liter range 总被引:5,自引:0,他引:5
Compound-specific carbon isotope analysis (CSIA) has become an important tool in biological, archeological, and geological studies as well as in forensics, food sciences, and organic chemistry. If sensitivity could be enhanced, CSIA would further have an improved potential for environmental applications such as, for example, in situ remediation studies to assess contaminated environments, identification of pollutant degradation pathways and kinetics, distinction between degradation/formation mechanisms, or, verification of contaminant sources. With this goal in mind, we have developed methods to determine delta13C values of commonly reported groundwater contaminants in low-microgram per liter concentrations. Several injection and preconcentration techniques were evaluated for this purpose, i.e., on-column injection, split/ splitless injection, solid-phase microextraction (SPME), and purge and trap (P&T) in combination with gas chromatography-isotope ratio mass spectrometry. The delta13C values of the target compounds were determined by liquid injections of the analytes dissolved in diethyl ether or, in the case of P&T and SPME, by extraction from water spiked with the analytes. P&T extraction was the most efficient preconcentration technique reaching method detection limits (MDLs) from 0.25 to 5.0 microg/L. These are the lowest MDLs reported so far for continuous-flow isotope ratio determinations, using a commercially available and fully automated system. Isotopic fractionation resulting from preconcentration and injection was investigated and quantified for the priority groundwater pollutants methyl tert-butyl ether (MTBE), chloroform, tetrachloromethane, chlorinated ethylenes, benzene, and toluene. The isotopic fractionations caused by the extraction techniques were small but highly reproducible and could therefore be corrected for. P&T was characterized by a higher reproducibility and smaller isotopic fractionations than SPME. Among the liquid injection techniques, cold on-column injection resulted in slightly better precision compared to split/splitless injection. However, the MDLs determined for liquid injections were 4-6 orders of magnitude higher (i.e., 9.5-2800 mg/L) than for P&T and SPME. Since both of the latter methods are solventless, a better chromatographic resolution was obtained than for the liquid injection techniques. The P&T and SPME methods described here are also applicable for CSIA of D/H ratios, which require 10-20 times higher analyte concentrations than 13C/12C analysis. Finally, the applicability of the described methods is demonstrated for pollutant concentrations of only 5-60 microg/L in environmental samples. 相似文献
85.
The final stages of sperm differentiation occur outside the gonad and are not under the genomic control of germ cells. Only sequential interactions with the medium surrounding the sperm are believed to induce the final steps of spermatogenesis. The epididymis, a long tubule with very active secretory and reabsorption functions, is able to create sequential changes in the composition of luminal fluid throughout its length. The chronologies of the changes, which occur on/in the sperm with those in their surrounding environment, are described. Correlations between the highly regionalized epididymal activities and sperm characteristics linked to their survival and fertility potential are presented in this review. 相似文献
86.
The introduction of the double bond in the sphingoid backbone of sphingolipids occurs at the level of dihydroceramide via an NADPH-dependent desaturase, as discovered in permeabilized rat hepatocytes. In the rat, the enzyme activity, which has
now been further characterized, appeared to be mostly enriched in liver and Harderian gland. By means of subcellular fractionation
of rat liver homogenates and density gradient separation of microsomal fractions, the desaturase was localized to the endoplasmic
reticulum. Various detergents were inhibitory to the enzyme, and maximal activities were obtained in the presence of NADPH
and when the substrate was complexed to albumin. In the presence of albumin, the chain length of the fatty acid of the truncated
dihydroceramides hardly affected the activity. Finally, in view of a likely evolutionary relationship between desaturases
and hydroxylases, the formation of hydroxylated intermediates was analyzed. No evidence for their presence was found under
our assay conditions.
In part presented at the Conférence Jacques Monod “Cell lipids: Topology, transport and signalling functions”, Aussois, May
1997 (France); Van Veldhoven, P.P. “Ceramide biosynthesis: Characterisation of the conversion of dihydroceramide to ceramide”.
Contributed equally to this study. 相似文献
87.
Pradip Mainali Gauthier Lafruit Qiong Yang Bert Geelen Luc Van Gool Rudy Lauwereins 《International Journal of Computer Vision》2013,104(2):172-197
We present a new method to extract scale-invariant features from an image by using a Cosine Modulated Gaussian (CM-Gaussian) filter. Its balanced scale-space atom with minimal spread in scale and space leads to an outstanding scale-invariant feature detection quality, albeit at reduced planar rotational invariance. Both sharp and distributed features like corners and blobs are reliably detected, irrespective of various image artifacts and camera parameter variations, except for planar rotation. The CM-Gaussian filters are approximated with the sum of exponentials as a single, fixed-length filter and equal approximation error over all scales, providing constant-time, low-cost image filtering implementations. The approximation error of the corresponding digital signal processing is below the noise threshold. It is scalable with the filter order, providing many quality-complexity trade-off working points. We validate the efficiency of the proposed feature detection algorithm on image registration applications over a wide range of testbench conditions. 相似文献
88.
François Nicot Nejib Hadda Franck Bourrier Luc Sibille Félix Darve 《Granular Matter》2011,13(3):255-260
This paper attempts to numerically validate the concept of diffuse failure using a discrete element method. First, the theoretical
background is reviewed, and it is shown how the kinetic energy of a system, initially at rest after a loading history, is
likely to abruptly increase under the effect of disturbances. The vanishing of the second-order work thus constitutes a basic
ingredient, related to both the pioneering work of Hill (J Mech Phys Solids (6):236–249, 1958) and the notion of bifurcation applied to geomechanics (Vardoulakis and Sulem in Bifurcation analysis in geomechanics, Chapman
& Hall Publisher, London, 1995). Discrete numerical simulations were performed on homogeneous three-dimensional specimens, and the three basic conditions
that must be satisfied in order to observe a failure mechanism are numerically checked. Finally, this work illustrates the
phenomena that are likely to affect in situ slopes, for instance, when the loading (due to weather conditions or human activities)
meets the three basic conditions for a failure mechanism to develop. 相似文献
89.
While current crisis management literature focuses on the necessity of consistent data and shared interpretation to coordinate effectively, contrastingly, this paper highlights the predominating influence of crisis responders' performances on information transmission. Based on an exploratory interpretive analysis of the 2003 French heat wave crisis response, our findings reveal that performances can support immediate reaction and involvement, but can also generate conflicts or misunderstandings that may burden coordination. This work's contribution to the crisis management literature is in threefold. First, we enrich the crisis management literature by proposing performativity as a potential analytical lens for collective action during crisis response. Second, we propose some practical recommendations to improve crisis management training through the application of the concept of performativity. Finally, we propose a critical perspective on tacitly held assumptions in crisis management. 相似文献
90.
Luc Florack Evgeniya Balmashnova Laura Astola Ellen Brunenberg 《Journal of Mathematical Imaging and Vision》2010,38(3):171-181
Single-shell high angular resolution diffusion imaging data (HARDI) may be decomposed into a sum of eigenpolynomials of the
Laplace-Beltrami operator on the unit sphere. The resulting representation combines the strengths hitherto offered by higher
order tensor decomposition in a tensorial framework and spherical harmonic expansion in an analytical framework, but removes
some of the conceptual weaknesses of either. In particular it admits analytically closed form expressions for Tikhonov regularization
schemes and estimation of an orientation distribution function via the Funk-Radon Transform in tensorial form, which previously
required recourse to spherical harmonic decomposition. As such it provides a natural point of departure for a Riemann-Finsler
extension of the geometric approach towards tractography and connectivity analysis as has been stipulated in the context of
diffusion tensor imaging (DTI), while at the same time retaining the natural coarse-to-fine hierarchy intrinsic to spherical
harmonic decomposition. 相似文献