全文获取类型
收费全文 | 720247篇 |
免费 | 9137篇 |
国内免费 | 2597篇 |
专业分类
电工技术 | 12911篇 |
综合类 | 1004篇 |
化学工业 | 106982篇 |
金属工艺 | 27663篇 |
机械仪表 | 20886篇 |
建筑科学 | 17392篇 |
矿业工程 | 3447篇 |
能源动力 | 19490篇 |
轻工业 | 61203篇 |
水利工程 | 7398篇 |
石油天然气 | 13616篇 |
武器工业 | 75篇 |
无线电 | 82670篇 |
一般工业技术 | 140656篇 |
冶金工业 | 140457篇 |
原子能技术 | 15587篇 |
自动化技术 | 60544篇 |
出版年
2021年 | 6349篇 |
2020年 | 4612篇 |
2019年 | 5914篇 |
2018年 | 10106篇 |
2017年 | 10002篇 |
2016年 | 10511篇 |
2015年 | 7206篇 |
2014年 | 12055篇 |
2013年 | 32581篇 |
2012年 | 19145篇 |
2011年 | 26546篇 |
2010年 | 20757篇 |
2009年 | 23575篇 |
2008年 | 24095篇 |
2007年 | 23833篇 |
2006年 | 20747篇 |
2005年 | 18927篇 |
2004年 | 18449篇 |
2003年 | 18193篇 |
2002年 | 17312篇 |
2001年 | 17453篇 |
2000年 | 16208篇 |
1999年 | 17179篇 |
1998年 | 44053篇 |
1997年 | 30930篇 |
1996年 | 23686篇 |
1995年 | 17813篇 |
1994年 | 15623篇 |
1993年 | 15421篇 |
1992年 | 11079篇 |
1991年 | 10490篇 |
1990年 | 10223篇 |
1989年 | 9964篇 |
1988年 | 9246篇 |
1987年 | 8316篇 |
1986年 | 8205篇 |
1985年 | 9058篇 |
1984年 | 8482篇 |
1983年 | 7598篇 |
1982年 | 7170篇 |
1981年 | 7248篇 |
1980年 | 7000篇 |
1979年 | 6728篇 |
1978年 | 6626篇 |
1977年 | 7725篇 |
1976年 | 10235篇 |
1975年 | 5655篇 |
1974年 | 5387篇 |
1973年 | 5521篇 |
1972年 | 4530篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
931.
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
932.
A membrane reactor containing different types of ZSM-5/porous SS membranes was used to perform the xylene isomerization reaction. The parent Na-ZSM-5 layer was synthesized by secondary growth on top of porous stainless steel tubes. The xylene isomerization reaction was carried out at different temperatures in the membrane reactor and in a fixed-bed reactor of identical geometry for comparison. Two different kinds of membranes were prepared by ion exchange: a Pt/H-ZSM-5 catalytic membrane and two Ba-ZSM-5 composites with different Ba2+ concentration. The p-xylene production using 100% exchanged Ba-membrane was about 28% higher than the fixed-bed reactor at 370 °C, when m-xylene was fed. 相似文献
933.
The photoelectric parameters of silicon solar cells degraded under the action of 60Co gamma-radiation can be partly restored using an ultrasonic treatment (UST). The growth of the maximum output power of solar cells after the UST is related to a redistribution of the radiation defects and an increase in the homogeneity of a semiconductor crystal structure. 相似文献
934.
Power distribution systems have been significantly affected by many outage-causing events. Good fault cause identification can help expedite the restoration procedure and improve the system reliability. However, the data imbalance issue in many real-world data sets often degrades the fault cause identification performance. In this paper, the E-algorithm, which is extended from the fuzzy classification algorithm by Ishibuchi to alleviate the effect of imbalanced data constitution, is applied to Duke Energy outage data for distribution fault cause identification. Three major outage causes (tree, animal, and lightning) are used as prototypes. The performance of E-algorithm on real-world imbalanced data is compared with artificial neural network. The results show that the E-algorithm can greatly improve the performance when the data are imbalanced 相似文献
935.
R. A. Borzooei M. Bakhshi M. Mashinchi 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2008,12(8):739-749
In this paper, we study the lattice structure of some fuzzy algebraic systems such as (G-)fuzzy groups, some fuzzy ordered
algebras and fuzzy hyperstructures. We prove that under suitable conditions, these structures form a distributive or modular
lattice.
This research partially is supported by the “ Fuzzy Systems and its Applications Center of Excelence, Shahid Bahonar University
of Kerman, Iran”. 相似文献
936.
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
937.
Electronic textiles, or e-textiles, are an increasingly important part of wearable computing, helping to make pervasive devices truly wearable. These soft, fabric-based computers can function as lovely embodiments of Mark Weiser's vision of ubiquitous computing: providing useful functionality while disappearing discreetly into the fabric of our clothing. E-textiles also give new, expressive materials to fashion designers, textile designers, and artists, and garments stemming from these disciplines usually employ technology in visible and dramatic style. Integrating computer science, electrical engineering, textile design, and fashion design, e-textiles cross unusual boundaries, appeal to a broad spectrum of people, and provide novel opportunities for creative experimentation both in engineering and design. Moreover, e-textiles are cutting- edge technologies that capture people's imagination in unusual ways. (What other emerging pervasive technology has Vogue magazine featured?) Our work aims to capitalize on these unique features by providing a toolkit that empowers novices to design, engineer, and build their own e-textiles. 相似文献
938.
Isler V. Magdon-Ismail M. 《Automation Science and Engineering, IEEE Transactions on》2008,5(4):651-660
We address the sensor selection problem which arises in tracking and localization applications. In sensor selection, the goal is to select a small number of sensors whose measurements provide a good estimate of a target's state (such as location). We focus on the bounded uncertainty sensing model where the target is a point in the d -dimensional Euclidean space. Each sensor measurement corresponds to a convex polyhedral subset of the space. The measurements are merged by intersecting corresponding sets. We show that, on the plane, four sensors are sufficient (and sometimes necessary) to obtain an estimate whose area is at most twice the area of the best possible estimate (obtained by intersecting all measurements). We also extend this result to arbitrary dimensions and show that a constant number of sensors suffice for a constant factor approximation in arbitrary dimensions. Both constants depend on the dimensionality of the space but are independent of the total number of sensors in the network. 相似文献
939.
Stevens M. Williams P.D. Peterson G.L. Kurkowski S.H. 《Computational Intelligence Magazine, IEEE》2008,3(2):65-68
This research supports the hypothesis that the Trust Vector model can be modified to fit the CyberCraft Initiative, and that there are limits to the utility of historical data. This research proposed some modifications and expansions to the Trust Model Vector, and identified areas for future research. 相似文献
940.
Evolving artificial neural network ensembles 总被引:3,自引:0,他引:3
Using a coordinated group of simple solvers to tackle a complex problem is not an entirely new idea. Its root could be traced back hundreds of years ago when ancient Chinese suggested a team approach to problem solving. For a long time, engineers have used the divide-and-conquer strategy to decompose a complex problem into simpler sub-problems and then solve them by a group of solvers. However, knowing the best way to divide a complex problem into simpler ones relies heavily on the available domain knowledge. It is often a manual process by an experienced engineer. There have been few automatic divide-and-conquer methods reported in the literature. Fortunately, evolutionary computation provides some of the interesting avenues to automatic divide-and-conquer methods. An in-depth study of such methods reveals that there is a deep underlying connection between evolutionary computation and ANN ensembles. Ideas in one area can be usefully transferred into another in producing effective algorithms. For example, using speciation to create and maintain diversity had inspired the development of negative correlation learning for ANN ensembles, and an in-depth study of diversity in ensembles. This paper will review some of the recent work in evolutionary approaches to designing ANN ensembles. 相似文献