全文获取类型
收费全文 | 781篇 |
免费 | 28篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 151篇 |
金属工艺 | 33篇 |
机械仪表 | 26篇 |
建筑科学 | 4篇 |
矿业工程 | 4篇 |
能源动力 | 35篇 |
轻工业 | 13篇 |
水利工程 | 1篇 |
石油天然气 | 17篇 |
无线电 | 70篇 |
一般工业技术 | 178篇 |
冶金工业 | 43篇 |
原子能技术 | 31篇 |
自动化技术 | 198篇 |
出版年
2023年 | 4篇 |
2022年 | 26篇 |
2021年 | 28篇 |
2020年 | 15篇 |
2019年 | 11篇 |
2018年 | 29篇 |
2017年 | 21篇 |
2016年 | 25篇 |
2015年 | 14篇 |
2014年 | 29篇 |
2013年 | 68篇 |
2012年 | 46篇 |
2011年 | 63篇 |
2010年 | 48篇 |
2009年 | 41篇 |
2008年 | 41篇 |
2007年 | 37篇 |
2006年 | 24篇 |
2005年 | 28篇 |
2004年 | 26篇 |
2003年 | 28篇 |
2002年 | 21篇 |
2001年 | 15篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 17篇 |
1997年 | 6篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有809条查询结果,搜索用时 0 毫秒
41.
42.
A liquid-cell shearing interferometer was developed to measure refractive-index variations (delta n) in transparent materials. The cell was filled with a liquid having a matched refractive index. The achieved resolution was better than 1/1000 of a fringe shift and resulted in a delta n measurement sensitivity down to 10(-7) for 1-mm-thick samples. A refractive-index increment in photothermorefractive glass of up to 5 x 10(-6) was observed after UV exposure at 325 nm. A refractive-index decrement of up to 1 x 10(-3) was observed after thermal development of the exposed sample. It was proved that photothermorefractive glass obeys the reciprocity law; i.e., delta n depends on the UV dosage but does not depend on the irradiance. 相似文献
43.
44.
The near-normal-incidence efficiencies of a 2400-groove/mm holographic master grating, a replica grating, and a multilayer grating are modeled in the soft-x-ray-extreme-ultraviolet (EUV) regions and are compared with efficiencies that are measured with synchrotron radiation. The efficiencies are calculated by the computer program PCGrate, which is based on a rigorous modified integral method. The theory of our integral method is described both for monolayer and multilayer gratings designated for the soft-x-ray-EUV-wavelength range. The calculations account for the groove profile as determined from atomic force microscopy with a depth scaling in the case of the multilayer grating and an average random microroughness (0.7 nm) for the short wavelengths. The refractive indices of the grating substrate and coatings have been taken from different sources because of the wide range of the wavelengths (4.5-50 nm). The measured peak absolute efficiency of 10.4% in the second diffraction order at a wavelength of 11.4 nm is achieved for the multilayer grating and is in good agreement with a computed value of approximately 11.5%. Rigorous modeling of the efficiencies of three similar gratings is in good overall agreement with the measured efficiency over a wide wavelength region. Additional calculations have indicated that relatively high normal incidence efficiency (of at least several percent) and large angular dispersion in the higher orders can be achieved in the 4.5-10.5-nm range by application of various multilayer coatings. 相似文献
45.
A vector (multicriterion) problem of integer linear programming is considered on a finite set of feasible solutions. A metric
lp, 1 ≤ p ≤ ∞, is defined on the parameter space of the problem. A formula of the maximum permissible level of perturbations
is obtained for the parameters that preserve the efficiency (Pareto optimality) of a given solution. Necessary and sufficient
conditions of two types of stability of the problem are obtained as corollaries.
This work has been carried out with financial support from the Belgosuniversity within the framework of the Intercollegiate
Program “Fundamental and Applied Investigations” (project No. 492/28).
__________
Translated from Kibernetika I Sistemnyi Analiz, No. 4, pp. 175–181, July–August 2006. 相似文献
46.
Sigal L Sclaroff S Athitsos V 《IEEE transactions on pattern analysis and machine intelligence》2004,26(7):862-877
A novel approach for real-time skin segmentation in video sequences is described. The approach enables reliable skin segmentation despite wide variation in illumination during tracking. An explicit second order Markov model is used to predict evolution of the skin-color (HSV) histogram over time. Histograms are dynamically updated based on feedback from the current segmentation and predictions of the Markov model. The evolution of the skin-color distribution at each frame is parameterized by translation, scaling, and rotation in color space. Consequent changes in geometric parameterization of the distribution are propagated by warping and resampling the histogram. The parameters of the discrete-time dynamic Markov model are estimated using Maximum Likelihood Estimation and also evolve over time. The accuracy of the new dynamic skin color segmentation algorithm is compared to that obtained via a static color model. Segmentation accuracy is evaluated using labeled ground-truth video sequences taken from staged experiments and popular movies. An overall increase in segmentation accuracy of up to 24 percent is observed in 17 out of 21 test sequences. In all but one case, the skin-color classification rates for our system were higher, with background classification rates comparable to those of the static segmentation. 相似文献
47.
The influence of red blood cell (RBC) aggregation on transparency of blood in the red-near infrared spectral range is investigated. We argue that for relatively thin blood layers the light diffraction on aggregates becomes the dominant phenomenon. The nature of pulsatile changes of blood transparency is explained by pulsations of RBC aggregate size. For another case of over-systolic vessel occlusion the following time evolution of blood transparency strongly depends on light wavelength. This dependence may serve as a basis for an alternative approach to noninvasive blood tests: occlusion spectroscopy. Theoretical results well correspond to both in vivo and in vitro measurements reproducing pulsatile blood flow and long occlusion as well. 相似文献
48.
We consider output feedback stabilization of uniformly observable uncertain nonlinear systems when the uncertain parameters belong to a known but comparably large compact set. In a previous paper, we proposed a new logic-based switching control to improve the performance of continuous high-gain-observer-based sliding mode controllers. Our main goal here is to show that similar techniques can be exploited for solving challenging control problems for a more general class of uncertain nonlinear systems. We require neither the sign of the high-frequency gain to be known nor the system to be minimum-phase. The key idea is to split the set of parameters into smaller subsets, design a controller for each of them, and switch the controller if, after a dwell-time period, the derivative of the Lyapunov function does not satisfy a certain inequality. A high-gain observer is used to estimate the derivatives of the output as well as the derivative of the Lyapunov function. Another goal of this paper is to introduce a switching strategy that uses on-line information to decide on the controller to switch to, instead of using a pre-sorted list as in our previous work. The new strategy can improve the transient performance of the system. 相似文献
49.
Atıcı Ramazan Sağır Selçuk Emelyanov Leonid Ya Lyashenko Mykhaylo 《Wireless Personal Communications》2021,118(4):2239-2251
Wireless Personal Communications - In the present study, the results obtained by incoherent scatter radar (ISR) and empirical models (NeQuick2 and IRI-2016) of the variations in mid-latitude... 相似文献
50.
Michael Ryvkin Moshe B. Fuchs Fabian Lipperman Leonid Kucherov 《International Journal of Fracture》2004,128(1-4):215-221
The periodic structure of some natural and especially man-made materials can be manifested not only on an atomic but also on a larger scale. Investigation of mechanical properties of these materials usually hinges on well-developed homogenization methods. On the other hand, these methods are not suitable for fracture analysis where the knowledge of the local stress-strain fields near a flaw (a crack) is required. The result is obtained by the use of the representative cell method based on the discrete Fourier transform. This method enables one to determine the exact stress distribution in a periodic structure subjected to arbitrary loading. Direct application of the method is impossible since the crack violates the translational symmetry defined by the material microstructure. This obstacle is overcome by application of the fictitious loading to the uncracked body at the line where the crack is to be located. The amplitude of the loading is adjusted in order to fulfill the boundary conditions imposed on the crack faces. The compatibility equation for deriving this amplitude is obtained by the use of the corresponding Green function, which is found in a closed form. Fracture problems for the two types of materials with a periodic microstructure are considered. The first one is a composite material consisting of dissimilar isotropic elastic layers arranged periodically. The second periodic microstructure is a 2D infinite beam lattice modeling a cellular material. The analysis of the failure process in the latter case shows that in contrast to the case of homogeneous material, the crack propagation path is not defined by the condition of zero Mode II stress intensity factor. 相似文献