全文获取类型
收费全文 | 12085篇 |
免费 | 1850篇 |
国内免费 | 1445篇 |
学科分类
工业技术 | 15380篇 |
出版年
2024年 | 76篇 |
2023年 | 297篇 |
2022年 | 423篇 |
2021年 | 562篇 |
2020年 | 550篇 |
2019年 | 456篇 |
2018年 | 432篇 |
2017年 | 438篇 |
2016年 | 589篇 |
2015年 | 559篇 |
2014年 | 727篇 |
2013年 | 703篇 |
2012年 | 744篇 |
2011年 | 804篇 |
2010年 | 695篇 |
2009年 | 722篇 |
2008年 | 771篇 |
2007年 | 738篇 |
2006年 | 702篇 |
2005年 | 634篇 |
2004年 | 559篇 |
2003年 | 437篇 |
2002年 | 423篇 |
2001年 | 363篇 |
2000年 | 304篇 |
1999年 | 222篇 |
1998年 | 170篇 |
1997年 | 165篇 |
1996年 | 153篇 |
1995年 | 133篇 |
1994年 | 118篇 |
1993年 | 93篇 |
1992年 | 97篇 |
1991年 | 79篇 |
1990年 | 49篇 |
1989年 | 50篇 |
1988年 | 30篇 |
1987年 | 16篇 |
1986年 | 25篇 |
1985年 | 37篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1975年 | 10篇 |
1966年 | 10篇 |
1965年 | 12篇 |
1964年 | 16篇 |
1958年 | 10篇 |
1956年 | 11篇 |
1955年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
S. K. Aslanov 《Combustion, Explosion, and Shock Waves》2006,42(4):450-455
The behavior of the blast wave from an exploding spherical volume is investigated mathematically over the entire range of
blast-wave propagation. The computational method uses analytical results for a similar problem for a point explosion with
counter pressure and the theory of an asymptotically equivalent point explosion. The asymptotic solution of the gas-dynamic
equations away from the explosion site is matched to the initial conditions of blast-wave formation due to the disintegration
of the detonation shock upon its arrival at the boundary of the exploding volume. The spatial distribution of the blast-front
pressure is found for combustible gaseous systems and solid explosives. The theoretical results obtained agree quantitatively
with available experimental measurements.
__________
Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 93–99, July–August, 2006. 相似文献
52.
53.
U. Reimer
H. -J. Schek
《Data & Knowledge Engineering》1989,4(4):321-352The first part of this paper introduces the basic constructs of a frame representation model and gives a formal definition for them. Subsequently the nested relational model (NF2) is described as an extension of the classical relational model to support relation-valued attributes. In the second part of this paper both models are compared with each other and a mapping of frame representation structures to NF2 structures is specified. The structural similarities between frames and NF2 relations are made clear and it is shown that their main difference is due to the type polymorphism introduced by the concept hierarchy of the frame model. This causes type collisions to occur in the strictly typed NF2 model when frames are directly mapped to NF2 structures. Two solutions to this problem are suggested and compared. The paper concludes with a reformulation of query operations of the frame model in terms of NF2 algebra operations. 相似文献
54.
Wei Hui 《Frontiers of Computer Science in China》2007,1(3):361-372
Almost all applications of Artificial Neural Networks (ANNs) depend mainly on their memory ability. The characteristics of
typical ANN models are fixed connections, with evolved weights, globalized representations, and globalized optimizations,
all based on a mathematical approach. This makes those models to be deficient in robustness, efficiency of learning, capacity,
anti-jamming between training sets, and correlativity of samples, etc. In this paper, we attempt to address these problems
by adopting the characteristics of biological neurons in morphology and signal processing. A hierarchical neural network was
designed and realized to implement structure learning and representations based on connected structures. The basic characteristics
of this model are localized and random connections, field limitations of neuron fan-in and fan-out, dynamic behavior of neurons,
and samples represented through different sub-circuits of neurons specialized into different response patterns. At the end
of this paper, some important aspects of error correction, capacity, learning efficiency, and soundness of structural representation
are analyzed theoretically. This paper has demonstrated the feasibility and advantages of structure learning and representation.
This model can serve as a fundamental element of cognitive systems such as perception and associative memory. 相似文献
55.
This study examined how 1 symbol is selected to control the allocation of attention when several symbols appear in the visual field. In Experiments 1-3, the critical target feature was color, and it was found that uninformative central arrows that matched the color of the target were selected and produced unintentional shifts of attention (i.e., involuntary, initiated slowly, producing long-lasting facilitatory effects). Experiment 4 tested whether such selection is the result of an attentional filter or of a competition bias due to a match of incoming information against integrated object representations stored in working memory. Here, the critical feature was shape and color was irrelevant, but matching color arrows were still selected. Thus, features of objects in working memory will bias the selection of symbols in the visual field, and such selected symbols are capable of producing unintentional shifts of attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
56.
The authors used visual search tasks in which components of the classic flanker task (B. A. Eriksen & C. W. Eriksen, 1974) were introduced. In several experiments the authors obtained evidence of parallel search for a target among distractor elements. Therefore, 2-stage models of visual search predict no effect of the identity of those distractors. However, clear compatibility effects of the distractors were obtained: Responses were faster when the distractors were compatible with the response than when they were incompatible. These results show that even in parallel search tasks identity information is extracted from the distractors. In addition, alternative interpretations of the results in terms of the occasional identification of a distractor before or after the target was identified could be ruled out. The results showed that flat search slopes obtained in visual search experiments provide no benchmark for preattentive processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
57.
Perkins Kenneth A.; Ciccocioppo Melinda; Jacobs Lynette; Doyle Todd; Caggiula Anthony 《Canadian Metallurgical Quarterly》2003,11(4):269
Nonpharmacological cues associated with drug intake may influence subjective and reinforcing effects of those drugs. Social drinkers (N = 80) participated in 2 sessions in which they rated and then consumed ad lib their preferred beer (with participants blind to brand). Visual and olfactory stimuli were obscured during 1 session (blocked) and not obscured during the other (unblocked). Dependent measures included ratings of "liking", "want another", and "desire to drink"; subjective mood; and ad lib beer consumption (reinforcement). Most ratings and ad lib consumption were lower during the blocked versus the unblocked condition. There were no interactions of blockade condition with sex and no effect of blockade on mood. These findings show that nonpharmacological stimuli associated with alcohol consumption influence alcohol's subjective and reinforcing effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
58.
论科技论文英语摘要的表现形式 总被引:1,自引:0,他引:1
王定全 《武汉工业学院学报》2005,24(2):109-112
论述科技论文中英语摘要的文体风格、时态、语态和基本要求,并结合例句介绍了常用的表现形式,使之简洁、准确和流畅。 相似文献
59.
60.
The present article reports the investigation of the effects of surrounding brightness on a visual search for three safety colors: red, orange, and yellow. Images of visual stimuli consisting of an array of colored circles placed on a large visual field (a visual angle of 40°) were displayed on an 80‐in. screen with a DLP projector. Experiment I examined the search efficiency under three levels of background luminance that were equivalent to the three target luminances. The results showed that the search efficiency for the orange target decreased as the number of distractors increased, under each of the background luminance levels, whereas the efficiency scarcely decreased for the red and yellow targets. Although a reduction in background luminance increased the search efficiency for the orange target, it is suggested that the effect of background luminance is smaller than the effect of the target color in search efficiency. Experiment II examined the search efficiency under three conditions of low levels of incident illuminance, which were matched with a linear regression to the luminance of color chips of safety colors measured twilight conditions. The results showed that the search efficiency for the orange target decreased as the number of distractors increased under each of the different illuminance conditions, whereas the efficiency scarcely decreased for red and yellow targets. Furthermore, as illuminance decreased, the search time for the orange target was more greatly impacted than for red or yellow. These results imply that the recognition of orange tends to be influenced by the surrounding brightness. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 400–409, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20152 相似文献