全文获取类型
收费全文 | 2534篇 |
免费 | 110篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 33篇 |
综合类 | 8篇 |
化学工业 | 658篇 |
金属工艺 | 49篇 |
机械仪表 | 25篇 |
建筑科学 | 170篇 |
矿业工程 | 6篇 |
能源动力 | 77篇 |
轻工业 | 208篇 |
水利工程 | 20篇 |
石油天然气 | 5篇 |
无线电 | 237篇 |
一般工业技术 | 490篇 |
冶金工业 | 232篇 |
原子能技术 | 15篇 |
自动化技术 | 414篇 |
出版年
2023年 | 40篇 |
2022年 | 49篇 |
2021年 | 104篇 |
2020年 | 55篇 |
2019年 | 58篇 |
2018年 | 59篇 |
2017年 | 57篇 |
2016年 | 86篇 |
2015年 | 68篇 |
2014年 | 119篇 |
2013年 | 138篇 |
2012年 | 156篇 |
2011年 | 187篇 |
2010年 | 113篇 |
2009年 | 120篇 |
2008年 | 134篇 |
2007年 | 125篇 |
2006年 | 117篇 |
2005年 | 104篇 |
2004年 | 82篇 |
2003年 | 60篇 |
2002年 | 58篇 |
2001年 | 29篇 |
2000年 | 46篇 |
1999年 | 39篇 |
1998年 | 55篇 |
1997年 | 43篇 |
1996年 | 46篇 |
1995年 | 34篇 |
1994年 | 34篇 |
1993年 | 22篇 |
1992年 | 15篇 |
1991年 | 18篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1973年 | 5篇 |
1916年 | 4篇 |
排序方式: 共有2647条查询结果,搜索用时 15 毫秒
31.
OBJECTIVE: This study examined the way in which the type and preexisting strength of association between an auditory icon and a warning event affects the ease with which the icon/event pairing can be learned and retained. BACKGROUND: To be effective, an auditory warning must be audible, identifiable, interpretable, and heeded. Warnings consisting of familiar environmental sounds, or auditory icons, have potential to facilitate identification and interpretation. The ease with which pairings between auditory icons and warning events can be learned and retained is likely to depend on the type and strength of the preexisting icon/event association. METHOD: Sixty-three participants each learned eight auditory-icon/denotative-referent pairings and attempted to recall them 4 weeks later. Three icon/denotative-referent association types (direct, related, and unrelated) were employed. Participants rated the strength of the association for each pairing on a 7-point scale. RESULTS: The number of errors made while learning pairings was greater for unrelated than for either related or direct associations, whereas the number of errors made while attempting to recall pairings 4 weeks later was greater for unrelated than for related associations and for related than for direct associations. Irrespective of association type, both learning and retention performance remained at very high levels, provided the strength of the association was rated greater than 5. CONCLUSION: This suggests that strong preexisting associations are used to facilitate learning and retention of icon/denotative-referent pairings. APPLICATION: The practical implication of this study is that auditory icons having either direct or strong, indirect associations with warning events should be preferred. 相似文献
32.
33.
Gietzelt M Schnabel S Wolf KH Büsching F Song B Rust S Marschollek M 《Computer methods and programs in biomedicine》2012,106(2):97-103
One of the key problems in accelerometry based gait analyses is that it may not be possible to attach an accelerometer to the lower trunk so that its axes are perfectly aligned to the axes of the subject. In this paper we will present an algorithm that was designed to virtually align the axes of the accelerometer to the axes of the subject during walking sections. This algorithm is based on a physically reasonable approach and built for measurements in unsupervised settings, where the test persons are applying the sensors by themselves. For evaluation purposes we conducted a study with 6 healthy subjects and measured their gait with a manually aligned and a skewed accelerometer attached to the subject's lower trunk. After applying the algorithm the intra-axis correlation of both sensors was on average 0.89±0.1 with a mean absolute error of 0.05g. We concluded that the algorithm was able to adjust the skewed sensor node virtually to the coordinate system of the subject. 相似文献
34.
One of the side-effects of the climate changes that are upon us is that infectious diseases are adapting, evolving and spreading to new geographic regions. It is, therefore, imperious to develop epidemic models that shed light on the interplay between the dynamics of the spread of infectious diseases and the combined effects of various vaccination and prevention regimens. With this in mind, in this work we propose a epidemic model operating on a large population; we restrict our attention to strains of infectious diseases that resist treatment. The time-dependent epidemic accounts, among others, for the effects of improved sanitation, education and vaccination. Our first main contribution is to derive the time-dependent probability mass function of the number of infected individuals in such a system. Our derivation does not use probability generating functions and partial differential equations. Instead, we develop an iterative solution that is conceptually simple and easy to implement. Somewhat surprisingly, the epidemic model also provides insight into various stochastic phenomena noticed in sociology, macroeconomics, marketing, transportation and computer science. Our second main contribution is to show, by extensive simulations, that suitably instantiated, our epidemic model be used to model phenomena describing the adoption of durable consumer goods, the spread of AIDS and the dissemination of mobile worm spread. 相似文献
35.
Photocatalytic degradation of a phenylurea, chlortoluron, in water using an industrial titanium dioxide coated media 总被引:1,自引:0,他引:1
Ludovic Lhomme Stephan Brosillon Dominique Wolbert Joseph Dussaud 《Applied catalysis. B, Environmental》2005,61(3-4):227-235
The degradation of an herbicide, chlortoluron, by UV/TiO2 photocatalysis in water using industrial titanium dioxide coated non-woven paper was studied. The influence of parameters such as adsorption capacity, initial concentration and TiO2 implementation (coated or in suspension) was investigated. The results emphasize the importance of operational conditions and reactor geometry on the kinetic degradation rate. The analysis of the first organic by-products suggests that a hydroxyl radical attack occurs on the phenyl ring and methyl groups of the chlortoluron before the opening of the aromatic ring. The fate of hetero-atoms has been investigated. The fates of the two nitrogen atoms in the molecule are different, not only did it depend on their initial oxidation degree, as both had the same oxidation degree, but also on the initial oxidation state of neighboring carbons. The chlorine atoms were completely released as chloride ions. The study of the influence of the oxygen concentration showed the importance of the oxygen mass transfer when designing an industrial photocatalytic reactor. An original calculation process was carried out to evaluate the adsorption constant of oxygen over the whole photocatalysis period and not only in the initial conditions as previously provided. This work points out the necessity of extending the understanding of the efficiency of chlortoluron removal or of the removal of various complex pesticide mixtures found in agricultural wastewater, using alternative, more industrially realistic, reactors. 相似文献
36.
Frank Schilder Werner Vogt Stephan Schreiber Hinke M. Osinga 《International journal for numerical methods in engineering》2006,67(5):629-671
Quasi‐periodic oscillations and invariant tori play an important role in the study of forced or coupled oscillators. This paper presents two new numerical methods for the investigation of quasi‐periodic oscillations. Both algorithms can be regarded as generalizations of the averaging and the harmonic (spectral) balance methods. The algorithms are easy to implement and require only minimal a priori knowledge of the system. Most importantly, the methods do not depend on an a priori co‐ordinate transformation. The methods are applied to a number of illustrative examples from non‐linear electrical engineering and the results show that the methods are efficient and reliable. In addition, these examples show that the presented algorithms can also continue through regions of sub‐harmonic (phase‐locked) resonance even though they are designed only for the quasi‐periodic case. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
37.
38.
Gold introduced the notion of learning in the limit where a class S is learnable iff there is a recursive machine M which reads the course of values of a function f and converges to a program for f whenever f is in S. An important measure for the speed of convergence in this model is the quantity of mind changes before the onset of convergence. The oldest model is to consider a constant bound on the number of mind changes M makes on any input function; such a bound is referred here as type 1. Later this was generalized to a bound of type 2 where a counter ranges over constructive ordinals and is counted down at every mind change. Although ordinal bounds permit the inference of richer concept classes than constant bounds, they still are a severe restriction. Therefore the present work introduces two more general approaches to bounding mind changes. These are based on counting by going down in a linearly ordered set (type 3) and on counting by going down in a partially ordered set (type 4). In both cases the set must not contain infinite descending recursive sequences. These four types of mind changes yield a hierarchy and there are identifiable classes that cannot be learned with the most general mind change bound of type 4. It is shown that existence of type 2 bound is equivalent to the existence of a learning algorithm which converges on every (also nonrecursive) input function and the existence of type 4 is shown to be equivalent to the existence of a learning algorithm which converges on every recursive function. A partial characterization of type 3 yields a result of independent interest in recursion theory. The interplay between mind change complexity and choice of hypothesis space is investigated. It is established that for certain concept classes, a more expressive hypothesis space can sometimes reduce mind change complexity of learning these classes. The notion of mind change bound for behaviourally correct learning is indirectly addressed by employing the above four types to restrict the number of predictive errors of commission in finite error next value learning (NV′′)—a model equivalent to behaviourally correct learning. Again, natural characterizations for type 2 and type 4 bounds are derived. Their naturalness is further illustrated by characterizing them in terms of branches of uniformly recursive families of binary trees. 相似文献
39.
40.