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81.
Westbrook R. Frederick; Good Anthony J.; Kiernan Michael J. 《Canadian Metallurgical Quarterly》1997,111(5):996
A unilateral microinjection of morphine into the amygdala impaired fear conditioning to both a conditioned stimulus (CS) paired with shock and the context where shock occurred, whereas a microinjection of morphine into the nucleus accumbens (NA) spared fear conditioning to the CS but impaired, in a dose-dependent and receptor-specific manner, fear conditioning to the context. Morphine in the NA also spared extinction and latent inhibition of a CS but abolished the context specificity of these effects and eliminated the increase in discriminability that results from preexposure to a to-be-shocked context. The results identify a role for the NA in the processes by which rats learn about a context and are discussed in terms of an opioid disruption of either within-context associations or of attentional processes that contribute to such associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
82.
Westbrook L. Henning I. Nelson A. Fiddyment P. 《Quantum Electronics, IEEE Journal of》1985,21(6):512-518
Spectral measurements of strongly coupled DFB lasers operating at 1.5 μm are presented. The magnitude of the coupling coefficientk in these devices was determined to be 80 cm-1for lasers withlambda = 1.12 mu m cladding layers and 160 cm-1for devices withlambda = 1.3 mu m cladding layers. These values fork are believed to be the largest reported for 1.5 μm DFB lasers. CW spectral linewidths as low as 10 MHz at 15 mW output power were obtained, and the linewidth was observed to vary approximately as the inverse of the device length cubed. Spectral measurements performed under 2 Gbit/s direct modulation exhibited a side mode suppression ratio of >38 dB. The effects of transient wavelength chirping were also investigated in detail and the maximum wavelength deviation was found to be ≃1.5 Å. 相似文献
83.
Nondeterministic weighted finite-state automata are a key abstraction in automatic speech recognition systems. The efficiency
of automatic speech recognition depends directly on the sizes of these automata and the degree of nondeterminism present,
so recent research has studied ways to determinize and minimize them, using analogues of classical automata determinization
and minimization. Although, as we describe here, determinization can in the worst case cause poly-exponential blowup in the
number of states of a weighted finite-state automaton, in practice it is remarkably successful. In extensive experiments in
automatic speech recognition systems, deterministic weighted finite-state automata tend to be smaller than the corresponding
nondeterministic inputs. Our observations show that these size reductions depend critically on the interplay between weights
and topology in nondeterministic weighted finite-state automata. We exploit these observations to design a new approximate determinization algorithm, which produces a deterministic weighted finite-state automaton that preserves the strings of a weighted language
but not necessarily their weights. We apply our algorithm to two different types of weighted finite-state automata that occur
in automatic speech recognition systems and in each case provide extensive experimental results showing that, compared with
current techniques, we achieve significant size reductions without affecting performance. In particular, for a standard test
bed, we can reduce automatic speech recognition memory requirements by 25—35\percent with negligible effects on recognition
time and accuracy.
Received March 31, 1998; revised January 29, 1999. 相似文献
84.
C. G. Reuther Jr. R. D. Westbrook Wade H. Hoffman Jr. H. L. E. Vix E. A. Gastrock 《Journal of the American Oil Chemists' Society》1951,28(4):146-149
Conclusions The results indicate that 9 to 10% moisture in the meats is the best level for the preparation of cottonseed into flakes for
solvent extraction. At lower moisture the flakes contain more fines before and after agitation in solvent, and the percolation
rate of solvent through a flake bed is lower because of reduced particle size. At higher moisture the amount of oil in the
hulls from the beater is greater. Also the flakes produce more fines, and the percolation rate becomes slower because of the
softness and pliability of the flaked meat. It is likely that in commercial continuous operations this packing or balling
up tendency of the flaked meats may lead to periodic channeling or plugging in the extractor, dryer, conveyors, and filters.
These conclusions have been applied in the continuous pilot plant solvent extraction of three lots of prime cottonseed. The
results substantiate the findings herein and will be reported in a separate publication.
One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S.
Department of Agriculture. 相似文献
85.
D.R. Westbrook S. Chakrabarti Y.K. Cheung 《International Journal of Mechanical Sciences》1976,18(7-8)
This paper, a sequel to an earlier paper by the same authors, uses a three dimensional or penalty function approach to obtain finite element solutions for plate bending problems. The advantage in using this approach is that the finite element subspaces need only be continuous; the disadvantages are that more functions are needed.In our previous paper, we used piecewise quadratic and linear functions, in the present paper we use piecewise cubic and quadratic functions with a resultant reduction of the discretization error. We also suggest an interpolation method or an a priori choice of the thickness to length ratio which are appropriate for thin or moderately thick plates. Numerical results are given for clamped and simply supported plates with point and distributed loads. 相似文献
86.
D. R. Westbrook S. Chakrabarti Y. K. Cheung 《International Journal of Mechanical Sciences》1974,16(7):479-487
A three-dimensional finite element method is proposed for plate bending. The displacement function is assumed to have a particular form with respect to the thickness variable.The assumed displacement function is substituted into the three-dimensional potential energy functional and a two-dimensional variational problem emerges.The two-dimensional problem is treated by the finite element method and it is seen that for conforming solutions the only requirement is continuity of the basis functions.The method includes transverse shear and thickness effects and may be used for both thin and moderately thick shells.To illustrate the method and to compare it with other results, the problems of a square plate under point and distributed loads and with simply supported and clamped boundary are treated numerically. 相似文献
87.
Delamater Andrew R.; Campese Vincent; Westbrook R. Frederick 《Canadian Metallurgical Quarterly》2009,35(2):224
Previous research has reported a role for the neurotransmitter gamma-aminobutyric acid (GABA) in the extinction and renewal of conditioned fear. Here, the authors examine whether GABA is involved in the acquisition, extinction, renewal, spontaneous recovery, and latent inhibition of appetitive conditioning. Using Long-Evans rats, systemic injection of the GABA A receptor inverse agonist FG 7142 was shown to eliminate ABA renewal (Experiment 1) and spontaneous recovery (Experiment 4) of appetitive responding by selectively reducing the recovery of extinguished magazine approach. Furthermore, treatment with FG 7142 had no effects on acquisition or single-session extinction (Experiment 3) or on the context-specific expression of latent inhibition (Experiment 2). These data suggest that ABA renewal and spontaneous recovery, but not latent inhibition or responding during acquisition and an initial extinction session, are mediated by GABAergic mechanisms in appetitive Pavlovian conditioning. They provide support for the view that renewal and spontaneous recovery share a common psychological mechanism. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
88.
Five experiments studied retrograde impairments in Pavlovian fear conditioning following prolonged exposure to the opioid receptor agonist morphine. Injections of morphine commencing 1-7 days but not 14 days after conditioning produced amnesia for that conditioning episode. This amnesia was (a) selective such that morphine impaired freezing to the conditioning context but not to the auditory conditioned stimulus, (b) independent of the interval between the last injection of morphine and test, and (c) accompanied by a failure of contextual discrimination. Context preexposure protected context conditioning and discrimination from the amnestic effects of morphine. These results show that retrograde deficits in contextual fear conditioning are mediated by failures to consolidate a contextual representation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
89.
Harris Justin A.; Livesey Evan J.; Gharaei Saba; Westbrook R. Frederick 《Canadian Metallurgical Quarterly》2008,34(4):494
Two groups of rats were trained for 50 days on different discriminations in a magazine approach paradigm. One group was trained with a negative patterning schedule and a positive patterning schedule concurrently: they received intermixed trials of A+, B+, AB-, C-, D-, CD+ (A, B, C, and D are four distinct stimuli; the plus sign denotes reinforcement with food, and the minus sign denotes nonreinforcement). The second group of rats was trained with the same four stimuli arranged as compounds and reinforced according to the biconditional schedule AB+, CD+, AC-, and BD-. The first group learned the positive patterning schedule much more quickly than the negative patterning schedule, but they learned the negative patterning schedule more effectively than the second group learned the biconditional schedule. The authors discuss the implications of these findings for models of stimulus representation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
90.
Abstract. We present a new approach for designing external graph algorithms and use it to design simple, deterministic and randomized
external algorithms for computing connected components, minimum spanning forests, bottleneck minimum spanning forests, maximal
independent sets (randomized only), and maximal matchings in undirected graphs. Our I/ O bounds compete with those of previous approaches. We also introduce a semi-external model, in which the vertex set but
not the edge set of a graph fits in main memory. In this model we give an improved connected components algorithm, using new
results for external grouping and sorting with duplicates. Unlike previous approaches, ours is purely functional—without side
effects—and is thus amenable to standard checkpointing and programming language optimization techniques. This is an important
practical consideration for applications that may take hours to run. 相似文献