全文获取类型
收费全文 | 38280篇 |
免费 | 2184篇 |
国内免费 | 219篇 |
专业分类
电工技术 | 330篇 |
综合类 | 92篇 |
化学工业 | 5950篇 |
金属工艺 | 1070篇 |
机械仪表 | 726篇 |
建筑科学 | 1179篇 |
矿业工程 | 96篇 |
能源动力 | 595篇 |
轻工业 | 5543篇 |
水利工程 | 373篇 |
石油天然气 | 170篇 |
武器工业 | 2篇 |
无线电 | 1518篇 |
一般工业技术 | 4622篇 |
冶金工业 | 5779篇 |
原子能技术 | 163篇 |
自动化技术 | 12475篇 |
出版年
2024年 | 53篇 |
2023年 | 280篇 |
2022年 | 281篇 |
2021年 | 719篇 |
2020年 | 664篇 |
2019年 | 688篇 |
2018年 | 1250篇 |
2017年 | 1219篇 |
2016年 | 1275篇 |
2015年 | 976篇 |
2014年 | 1347篇 |
2013年 | 2585篇 |
2012年 | 2554篇 |
2011年 | 4677篇 |
2010年 | 2418篇 |
2009年 | 2105篇 |
2008年 | 1829篇 |
2007年 | 1639篇 |
2006年 | 1142篇 |
2005年 | 1175篇 |
2004年 | 1195篇 |
2003年 | 1220篇 |
2002年 | 803篇 |
2001年 | 650篇 |
2000年 | 513篇 |
1999年 | 397篇 |
1998年 | 2034篇 |
1997年 | 1263篇 |
1996年 | 779篇 |
1995年 | 477篇 |
1994年 | 356篇 |
1993年 | 335篇 |
1992年 | 101篇 |
1991年 | 86篇 |
1990年 | 81篇 |
1989年 | 102篇 |
1988年 | 100篇 |
1987年 | 93篇 |
1986年 | 82篇 |
1985年 | 89篇 |
1984年 | 101篇 |
1983年 | 54篇 |
1982年 | 48篇 |
1981年 | 72篇 |
1980年 | 71篇 |
1977年 | 116篇 |
1976年 | 220篇 |
1975年 | 42篇 |
1974年 | 43篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Martín A. Rodríguez Ricardo M. Carranza Raúl B. Rebak 《Metallurgical and Materials Transactions A》2005,36(5):1179-1185
Alloy 22 (N06022) is the current candidate alloy used to fabricate the external wall of the high-level nuclear waste containers
for the Yucca Mountain repository. It was of interest to study and compare the general and localized corrosion susceptibility
of Alloy 22 in fluoride and chloride solutions at 90 °C. Standard electrochemical tests such as cyclic potentiodynamic polarization,
amperometry, and electrochemical impedance spectroscopy were used. Studied variables included the solution pH and the alloy
microstructure (thermal aging). Results show that Alloy 22 is highly resistant to general corrosion in all the solutions tested.
Thermal aging is not detrimental and even seems to be slightly beneficial for general corrosion at the higher solution pHs.
Pitting corrosion was never observed. Crevice corrosion was found only for high chloride-containing solutions after anodic
polarization. The presence of fluoride ions together with chloride ions seems to increase the susceptibility of Alloy 22 to
crevice corrosion compared to pure chloride solutions.
This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste
Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion
and Environmental Effects and Nuclear Materials Committees. 相似文献
102.
The goal of face recognition is to distinguish persons via their facial images. Each person's images form a cluster, and a new image is recognized by assigning it to the correct cluster. Since the images are very high-dimensional, it is necessary to reduce their dimension. Linear discriminant analysis (LDA) has been shown to be effective at dimension reduction while preserving the cluster structure of the data. It is classically defined as an optimization problem involving covariance matrices that represent the scatter within and between clusters. The requirement that one of these matrices be nonsingular restricts its application to datasets in which the dimension of the data does not exceed the sample size. For face recognition, however, the dimension typically exceeds the number of images in the database, resulting in what is referred to as the small sample size problem. Recently, the applicability of LDA has been extended by using the generalized singular value decomposition (GSVD) to circumvent the nonsingularity requirement, thus making LDA directly applicable to face recognition data. Our experiments confirm that LDA/GSVD solves the small sample size problem very effectively as compared with other current methods. 相似文献
103.
104.
A stochastic realization problem of a stationary stochastic process is re-visited, and a new stochastically balanced realization algorithm is derived in a Hilbert space generated by second-order stationary processes. The present algorithm computes a stochastically balanced realization by means of the singular value decomposition of a weighted block Hankel matrix derived by a “block LQ decomposition”. Extension to a stochastic subspace identification method explains how the proposed abstract algorithm is implemented in system identification. 相似文献
105.
Sebastián López Gustavo M. Callicó Félix Tobajas Valentín de Armas José F. López Roberto Sarmiento 《ETRI Journal》2008,30(6):862-864
This letter presents a novel approach for organizing computational resources into groups within H.264/AVC motion estimation architectures, leading to reductions of up to 75% in the equivalent gate count with respect to state‐of‐the‐art designs. 相似文献
106.
107.
M Isabel Sánchez de Rojas Julián Rivera Moisés Frías Félix Marín 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):209-217
Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry 相似文献
108.
Joaquín Cortés Eliana Valencia Gonzalo Aguila Esteban Orellana Paulo Araya 《Catalysis Letters》2008,126(1-2):63-71
An experimental study is made of the time decay of activity of the CO–NO reaction on a Pd/Al2O3 looking at the effect on reaction order and apparent activation energy. The optimum kinetics parameters fitting the steady state data at moderate pressures are determined. The time decay curves are analyzed through various catalyst deactivation models. 相似文献
109.
In this paper, we analyze in some detail the manifold-mapping optimization technique introduced recently [Echeverría and Hemker in space mapping and defect correction. Comput Methods Appl Math 5(2): 107—136, 2005]. Manifold mapping aims at accelerating optimal design procedures that otherwise require many evaluations of time-expensive cost functions. We give a proof of convergence for the manifold-mapping iteration. By means of two simple optimization problems we illustrate the convergence results derived. Finally, the performances of several variants of the method are compared for some design problems from electromagnetics. 相似文献
110.
Reset controllers are linear controllers that reset some of their states to zero when their input is zero. We are interested in their feedback connection with linear plants, and in this paper we establish fundamental closed-loop properties including stability and asymptotic tracking. This paper considers more general reset structures than previously considered, allowing for higher-order controllers and partial-state resetting. It gives a testable necessary and sufficient condition for quadratic stability and links it to both uniform bounded-input bounded-state stability and steady-state performance. Unlike previous related research, which includes the study of impulsive differential equations, our stability results require no assumptions on the evolution of reset times. 相似文献