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51.
52.
We consider the problem of smoothing real-time streams (such as video streams), where the goal is to reproduce a variable-bandwidth stream remotely, while minimizing bandwidth cost, space requirement, and playback delay. We focus on lossy schedules, where data may be dropped due to limited bandwidth or space. We present the following results. First, we determine the optimal tradeoff between buffer space, smoothing delay, and link bandwidth for lossy smoothing schedules. Specifically, this means that if two of these parameters are given, we can precisely calculate the value for the third which minimizes data loss while avoiding resource wastage. The tradeoff is accomplished by a simple generic algorithm, that allows one some freedom in choosing which data to discard. This algorithm is very easy to implement both at the server and at the client, and it enjoys the nice property that only the server decides which data to discard, and the client needs only to reconstruct the stream.In a second set of results we study the case where different parts of the data have different importance, modeled by assigning a real weight to each packet in the stream. For this setting we use competitive analysis, i.e., we compare the weight delivered by on-line algorithms to the weight of an optimal off-line schedule using the same resources. We prove that a natural greedy algorithm is 4-competitive. We also prove a lower bound of 1.23 on the competitive ratio of any deterministic on-line algorithm. Finally, we give a few experimental results which seem to indicate that smoothing is very effective in practice, and that the greedy algorithm performs very well in the weighted case.Received: 21 November 2001, Accepted: 6 November 2003, Published online: 6 February 2004Research supported in part by Israel Ministry of Science. An extended abstract of this paper appeared in Proc. 19th ACM Symp. on Principles of Distributed Computing, July 2000. 相似文献
53.
54.
The learning-based automated Assume–Guarantee reasoning paradigm has been applied in the last few years for the compositional
verification of concurrent systems. Specifically, L* has been used for learning the assumption, based on strings derived from counterexamples, which are given to it by a model-checker
that attempts to verify the Assume–Guarantee rules. We suggest three optimizations to this paradigm. First, we derive from
each counterexample multiple strings to L*, rather than a single one as in previous approaches. This small improvement saves candidate queries and hence model-checking
runs. Second, we observe that in existing instances of this paradigm, the learning algorithm is coupled weakly with the teacher.
Thus, the learner completely ignores the details of the internal structure of the system and specification being verified,
which are available already to the teacher. We suggest an optimization that uses this information in order to avoid many unnecessary
membership queries (it reduces the number of such queries by more than an order of magnitude). Finally, we develop a method
for minimizing the alphabet used by the assumption, which reduces the size of the assumption and the number of queries required
to construct it. We present these three optimizations in the context of verifying trace containment for concurrent systems
composed of finite state machines. We have implemented our approach in the ComFoRT tool, and experimented with real-life examples. Our results exhibit an average speedup of between 4 to 11 times, depending
on the Assume–Guarantee rule used and the set of activated optimizations.
This research was supported by the Predictable Assembly from Certifiable Components (PACC) initiative at the Software Engineering
Institute, Pittsburgh. 相似文献
55.
Lobb Leslie; Stec Boguslaw; Kantrowitz Evan K.; Yamano Akihito; Stojanoff Vivian; Markman Ofer; Teeter Martha M. 《Protein engineering, design & selection : PEDS》1996,9(12):1233-1239
Crambin, a small hydrophobic protein (4.7 kDa and 46 residues),has been successfully expressed in Escherichia coli from anartificial, synthetic gene. Several expression systems wereinvestigated. Ultimately, crambin was successfully expressedas a fusion protein with the maltose binding protein, whichwas purified by affinity chromatography. Crambin expressed asa C-terminal domain was then cleaved from the fusion proteinwith Factor Xa protease and purified. Circular dichroism spectroscopyand amino acid analysis suggested that the purified materialwas identical to crambin isolated from seed. For positive identificationthe protein was crystallized from an ethanolwater solution,by a novel method involving the inclusion of phospholipids inthe crystallization buffer, and then subjected to crystallographicanalysis, Diffraction data were collected at the Brookhavensynchrotron (beamline-X12C) to a resolution of 1.32 Åat 150 K. The structure, refined to an R value of 9.6%, confirmedthat the cloned protein was crambin. The availability of clonedcrambin will allow site-specific mutagenesis studies to be performedon the protein known to the highest resolution. 相似文献
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57.
In this paper we present a method to extract qualitative information from any classification model that uses decision regions to generalize (e.g., feed-forward neural nets, SVMs, etc). The method's complexity is independent of the dimensionality of the input data or model, making it computationally feasible for the analysis of even very high-dimensional models. The qualitative information extracted by the method can be directly used to analyze the classification strategies employed by a model, and also to compare strategies across different model types. 相似文献
58.
59.
Within the visual system, docosahexaenoic acid (DHA, 22:6n−3) is an important structural component for retinal photoreceptors and cortical gray matter. There is a marked decrease in
neural DHA accumulation in the face of DHA deficiency. DHA is accumulated at an accelerated rate during pregnancy, especially
in the third trimester. However, pregnant women in the US and Canada have dietary DHA intakes that are significantly below
the optimal level. The main objective of this study was to determine whether a DHA-functional food during pregnancy would
benefit infant visual acuity at four and six months of age measured behaviorally using the acuity card procedure (ACP). In
a randomized, longitudinal, double-blinded, and placebo-controlled trial, 30 pregnant women received either the DHA-functional
food (n = 16) or the placebo (n = 14). There were significant main effects for visual acuity at four months of age (P = 0.018). The mean acuity scores were 3.8 ± 1.1 cycles/degree in the DHA group versus 3.2 ± 0.7 cycles/degree in the placebo
group. At six months there were no group differences. Based on our results, we conclude that DHA supplemented during pregnancy
plays a role in the maturation of the visual system. 相似文献
60.
The optimal allocation of resources at the firm level to transform emergent technological invention into commercially successful products depends on the effective assessment and selection of projects. This study develops a multidisciplinary model for differentiating, prioritizing, and selecting investment in technological projects within an organization’s portfolio. Approaches from project portfolio and strategic technology management are integrated to explore how a particular product within a diverse project portfolio may be prioritized and developed. Our results suggest that the application of the suggested model to a portfolio of biotechnology projects may enhance the assessment of internal capabilities and external competitiveness, thereby providing a basis for firms to prioritize and preferentially allocate scarce resources within a portfolio of heterogeneous technologies. 相似文献