全文获取类型
收费全文 | 2481篇 |
免费 | 109篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 31篇 |
综合类 | 8篇 |
化学工业 | 623篇 |
金属工艺 | 44篇 |
机械仪表 | 25篇 |
建筑科学 | 170篇 |
矿业工程 | 6篇 |
能源动力 | 71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 | 485篇 |
冶金工业 | 231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 | 103篇 |
2020年 | 54篇 |
2019年 | 57篇 |
2018年 | 58篇 |
2017年 | 56篇 |
2016年 | 85篇 |
2015年 | 67篇 |
2014年 | 119篇 |
2013年 | 136篇 |
2012年 | 154篇 |
2011年 | 185篇 |
2010年 | 112篇 |
2009年 | 115篇 |
2008年 | 130篇 |
2007年 | 120篇 |
2006年 | 116篇 |
2005年 | 104篇 |
2004年 | 82篇 |
2003年 | 55篇 |
2002年 | 55篇 |
2001年 | 29篇 |
2000年 | 46篇 |
1999年 | 37篇 |
1998年 | 55篇 |
1997年 | 43篇 |
1996年 | 45篇 |
1995年 | 34篇 |
1994年 | 34篇 |
1993年 | 20篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 9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2593条查询结果,搜索用时 15 毫秒
31.
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
32.
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
33.
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
34.
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
35.
36.
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
37.
38.
R. Krauss J. Luettmer-Strathmann J. V. Sengers K. Stephan 《International Journal of Thermophysics》1993,14(4):951-988
New equations for the thermal conductivity and the viscosity of R134a that are valid in a wide range of pressures and temperatures are presented. They were obtained through a theoretically based, critical evaluation of the available experimental data, which showed considerable inconsistencies between data sets, in particular in the vapor phase. In the critical region the observed enhancement in the thermal conductivity is well represented by a crossover model for the transport properties of fluids. Since thermodynamic properties enter into the calculation of the critical enhancement of the transport properties, a new fundamental equation for the critical region was developed also.Paper dedicated to Professor Joseph Kestin. 相似文献
39.
Stephan J. Maybank 《International Journal of Computer Vision》1995,16(1):5-33
The probability density function for the cross ratio is obtained under the hypothesis that the four image points have independent, identical, Gaussian distributions. The density function has six symmetries which are closely linked to the six different values of the cross ratio obtained by permuting the quadruple of points from which the cross ratio is calculated. The density function has logarithmic singularities corresponding to values of the cross ratio for which two of the four points are coincident. The cross ratio forms the basis of a simple system for recognising or classifying quadruples of collinear image points. The performance of the system depends on the choice of rule for deciding whether four image points have a given cross ratio . A rule is stated which is computationally straightforward and which takes into account the effects on the cross ratio of small errors in locating the image points. Two key properties of the rule are the probabilityR of rejection, and the probabilityF of a false alarm. The probabilitiesR andF depend on a thresholdt in the decision rule. There is a trade off betweenR andF obtained by varyingt. It is shown that the trade off is insensitive to the given cross ratio . LetF
w
=max
o
{F}. ThenR, F
w
are related approximately by
, provided –1
F
w
4. In the equation, is the accuracy with which image points can be located relative to the width of the image, andr
F
is a constant known as the normalised false alarm rate. In the range –1
F
w
4 the probabilitiesR andF
w
are related approximately by
. The value ofr
F
is 14.37. The consequences of these relations between R and Fw are discussed. It is conjectured that the above general form of the trade off betweenR andF
w
holds for a wide class of scalar invariants that could be used for model based object recognition. Invariants with the same type of trade off between the probability of rejection and the probability of false alarm are said to be nondegenerate for model based vision. 相似文献
40.
O. Lüning und Stephan Gerö 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1925,49(4):179-187
Ohne ZusammenfassungMitteilung aus der Nahrungsmittel-Untersuchungsstelle an der Technischen Hochschule in Braunschweig. 相似文献