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61.
Antenatal diagnosis of hereditary disease is highly dependent on sufficient theoretical knowledge and on a number of practical methods of studying the foetus such as obtaining, cultivating and assaying amniotic fluid cells. Knowledge of the primary defect in any monogenic disorder cannon be used in prenatal diagnosis unless the metabolic error is expressed in vitro. Modern cytogenetics can diagnose in utero a large majority of karyotyping abnormalities although the karyotype-phenotype correlation is not an absolute one. This task must be assigned to special laboratories where technical pitfalls are reliably avoided. In both metabolic and chromosomal hereditary disease, the pathologist can confirm and extend the phenotypic findings and improve knowledge on foetal features and physiopathology. Pathology is the more important, the less means of in utero diagnosis are available as in the non-chromosomal syndromes of localized or multiple malformations. Here it helps eliminating a present major drawback of prenatal diagnosis: the lack of a strict diagnosis in the previous patient in a family at risk. 相似文献
62.
63.
If we have two representations of a problem as constraint satisfaction problem (CSP) models, it has been shown that combining
the models using channeling constraints can increase constraint propagation in tree search CSP solvers. Handcrafting two CSP
models for a problem, however, is often time-consuming. In this paper, we propose model induction, a process which generates a second CSP model from an existing model using channeling constraints, and study its theoretical
properties. The generated induced model is in a different viewpoint, i.e., set of variables. It is mutually redundant to and can be combined with the input model,
so that the combined model contains more redundant information, which is useful to increase constraint propagation. We also
propose two methods of combining CSP models, namely model intersection and model channeling. The two methods allow combining
two mutually redundant models in the same and different viewpoints respectively. We exploit the applications of model induction,
intersection, and channeling and identify three new classes of combined models, which contain different amounts of redundant information. We construct combined models of permutation
CSPs and show in extensive benchmark results that the combined models are more robust and efficient to solve than the single
models. 相似文献
64.
A 3.1-10.6 GHz ultra-wideband two-stage pseudomorphit high electron mobility transistor low noise amplifier is presented. The first stage of the amplifier employs a resistive shunt feedback topology and two T-network sections to provide wideband input matching to a 50-Omega antenna. The current-sharing dc bias topology is used to ensure the low power consumption under fixed 3-V battery operation. The amplifier exhibits state of the art performance consuming only 12.9mW of dc power with a power gain of 12.5dB, plusmn0.5dB gain flatness, and 3.4-4.0dB noise figure. Input match is better than -12.0dB, output match is better than -15dB, and group delay is 184pSplusmn28pS 相似文献
65.
Electrostatic deposition of charged pesticide sprays onto biological targets may be undesirably limited under certain operational conditions by gaseous-discharge currents induced to flow between the incoming charged spray cloud and grounded points on the target (e.g. leaf tips). Spray deposition and charge transfer onto idealized target models as functions of target characteristics and intensity of spray-droplet charging are quantified experimentally to achieve a more fundamental understanding of this phenomenon. As compared to similar uncharged sprays, deposition onto smooth spherical, and planar targets was increased up to seven-fold and three-fold, respectively, at optimum spray-charge levels. Space-charge induced target ionization from a 20-mm point protrustion self-limited this electrostatic deposition to only a 3.5-fold increase for the spherical target but caused little reduction for the planar target. As compared with a hydraulic-atomizing nozzle, the charging nozzle increased deposition approximately eight-fold and 24-fold, respectively, onto the spherical and the planar targets. The ratios of charge-to-mass collected on all targets were unexpectedly found to exceed values calculated for the airborne charged-droplet cloud, indicating a possible contact-discharge during elastic collision of conductive droplets at the target. 相似文献
66.
In this paper we describe a biologically constrained architecture for developmental learning of eye–head gaze control on an iCub robot. In contrast to other computational implementations, the developmental approach aims to acquire sensorimotor competence through growth processes modelled on data and theory from infant psychology. Constraints help shape learning in infancy by limiting the complexity of interactions between the body and environment, and we use this idea to produce efficient, effective learning in autonomous robots. Our architecture is based on current thinking surrounding the gaze mechanism, and experimentally derived models of stereotypical eye–head gaze contributions. It is built using our proven constraint-based field-mapping approach. We identify stages in the development of infant gaze control, and propose a framework of artificial constraints to shape learning on the robot in a similar manner. We demonstrate the impact these constraints have on learning, and the resulting ability of the robot to make controlled gaze shifts. 相似文献
67.
Durability of lingo‐cellulosic fiber composites under environmental conditions such as moisture, freezing and thawing, and UV exposure needs to be determined prior to the use of these composite materials in outdoor applications. Dimensional stability and changes in the flexural strength and stiffness of extruded rice husk filled high‐density polyethylene composites with and without processing additives such as compatibilizers and processing aid were examined after exposing the composites to water, conditions of freeze–thaw cycles, and UV light. Water absorption results indicated a decrease in the rate of penetration of water in the composites in the presence of compatibilizers. The reduction in strength and stiffness after water absorption was lower for composites with compatibilizers than for the composites without any additives. Freezing and thawing experiments also showed the dimensional changes and degradation of strength and stiffness were less in composites with compatibilizers. Presence of processing aid in the composite showed a similar or enhanced water absorption and loss of mechanical properties, compared with those of the composite without processing additives. Although the composites showed a discoloration of the surface after the UV exposure time (745 h) studied, it was found that within this period of UV exposure the flexural strength and stiffness of the composites did not show significant change. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3619–3625, 2006 相似文献
68.
Yingjia Zhang Zuohua Huang Liangjie Wei Jiaxiang Zhang Chung K. Law 《Combustion and Flame》2012,159(3):918-931
Ignition delays of lean mixtures of methane–hydrogen with various hydrogen volumetric contents were experimentally studied in a shock tube together with modeling analysis. Results show that the ignition behavior of the methane–hydrogen mixture depending on pressure resembles that of methane for hydrogen fraction less than 40%, with the ignition delays decreasing with increasing pressure. For the hydrogen fraction equal 60%, a negligible promoted effect of pressure on the ignition of the methane–hydrogen mixture is exhibited. For hydrogen fractions equal or greater than 80%, however, the ignition response resembles that of hydrogen in that the ignition delay exhibits a complex dependence on pressure and two-step transition in the global activation energy. Compared with calculated values using four available mechanisms, the NUI Galway mechanism yielded the closest agreement, and was adopted in the sensitivity analysis of the ignition kinetics. The sensitivity analysis well explained the experimental results which the ignition delay decreases with increasing temperature regardless of whether methane (typical fuel 80%CH4/20%H2) or hydrogen (typical fuel 20%CH4/80%H2) dominates the ignition process. Rate of production analysis shows that the promoted effect of the hydrogen on the oxidation of the methane is mainly due to the concentrations of the free radicals such as H, O and OH increase with increasing hydrogen fraction, and lead to the total reaction rate is enhanced. Consumption of methane is mainly through these reactions in which the active free radicals participate. 相似文献
69.
70.
A note on smoke plumes from fires in multi-level shopping malls 总被引:4,自引:0,他引:4
M. Law 《Fire Safety Journal》1986,10(3):197-202
It is shown that the experimental data obtained for plume flow in model-scale shopping malls can be correlated using equations similar to those developed by Yokoi. Further analysis is needed to establish the effective source of the plumes and the range of validity of the correlations developed. An alternative method of calculating mass flow above a balcony is suggested for interim use, until further analysis has been carried out. 相似文献