全文获取类型
收费全文 | 759篇 |
免费 | 43篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 17篇 |
综合类 | 1篇 |
化学工业 | 157篇 |
金属工艺 | 48篇 |
机械仪表 | 15篇 |
建筑科学 | 4篇 |
矿业工程 | 2篇 |
能源动力 | 47篇 |
轻工业 | 47篇 |
水利工程 | 8篇 |
石油天然气 | 2篇 |
无线电 | 97篇 |
一般工业技术 | 177篇 |
冶金工业 | 78篇 |
原子能技术 | 6篇 |
自动化技术 | 99篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 16篇 |
2021年 | 33篇 |
2020年 | 21篇 |
2019年 | 23篇 |
2018年 | 24篇 |
2017年 | 34篇 |
2016年 | 37篇 |
2015年 | 24篇 |
2014年 | 25篇 |
2013年 | 50篇 |
2012年 | 41篇 |
2011年 | 51篇 |
2010年 | 40篇 |
2009年 | 31篇 |
2008年 | 48篇 |
2007年 | 31篇 |
2006年 | 31篇 |
2005年 | 18篇 |
2004年 | 16篇 |
2003年 | 19篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 17篇 |
1997年 | 21篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1985年 | 11篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1972年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有805条查询结果,搜索用时 359 毫秒
41.
No cloning theorem is a very fundamental issue in quantum mechanics. But the issue is much more involved if we consider quantum
state shared among two or more than two parties and allow only local operation and classical communication. In the context
of the fact that no known bipartite entangled state can be cloned by local operation and classical communication (LOCC) without
assistance of extra entangled state, the cloning of unknown orthogonal entangled state becomes meaningful when there is some
supply of free entanglement. With restriction on supply of free entanglement, various cases have been studied. In this paper,
we try to give an overview of the subject and results that have been obtained across the literature along with a new result
on probabilistic LOCC cloning of four Bell states. 相似文献
42.
L. E. Kar’kina I. L. Yakovleva V. M. Schastlivtsev 《Russian Metallurgy (Metally)》2011,2011(4):303-306
Transmission electron microscopy is used to analyze the evolution of the microstructure of steel 120G4 after complete and partial pearlitic transformation and subsequent heating to 680–1200°C. It is found that, as the heating temperature increases, the fraction of a carbide phase decreases and the character of an austenitic defect structure changes from microtwins and stacking faults to dislocations. 相似文献
43.
L. E. Kar’kina I. N. Kar’kin Yu. N. Gornostyrev 《The Physics of Metals and Metallography》2010,109(3):211-219
The process of formation of facets (faceting) in Ni, Al, and Au nanoparticles has been investigated by the molecular-dynamics
method. It has been established that the surface of nanoparticles of fcc metals with attainment of a low-energy habit can
be transformed via correlated displacements of atomic groups of the facet in the octahedral plane. It has been shown that
such a process is similar to the surface diffusion of atomic n-mers with the activation energy depending on the facet size, and for particles with a diameter d < 3.0 nm the correlated displacement of atomic layers proves to be the dominant mechanism of faceting. 相似文献
44.
Rapid synthesis of long calcium copper titanate (CCTO) nanorods was carried out by sequential annealing. CCTO thin films have been deposited on p-Si substrate by RF sputtering technique and afterwards, the samples were thermally treated using a preheated furnace by varying the annealing temperature from 850 °C to 1100 °C. CCTO nanorods of 12 µm lengths and 400–600 nm diameters were synthesized at 1100 °C. Based on the FESEM observations, a plausible growth mechanism has been proposed to explain the formation of nanorods. The (220) XRD peak of the CCTO film became prominent for the annealing temperature of 950 °C. The presence of nanoscale crystals in amorphous matrix has been observed by HRTEM studies. The elemental mapping of CCTO nanorod has shown a spatial variation of elements throughout the nanorod. The oxide and interface charge density was found to be increased with the rise in annealing temperature. 相似文献
45.
We have investigated laser action in a binary mixture of dyes, Rh-6G and DCM, resulting in tunable laser emission over an extended frequency region. The two dyes absorb the same pump radiation but fluoresce over frequency ranges that are shifted with respect to each other, thereby resulting in extended tunability. Following a time-dependent analysis of a rate-equation model that describe the operation of such a laser, theoretical estimates for optimum dye concentrations and the corresponding extension of the laser tuning range have been obtained. 相似文献
46.
Partition coefficients of phenol, salicylic acid, and several environmentally important chloro- and nitrophenols in a supercritical CO2-water system were measured using direct cocurrent extraction of aqueous solutions of the individual solutes with CO2. Partitioning data on the nitrophenols and salicylic acid were obtained for the first time. To bypass the troublesome and error-prone analysis of the CO2-rich phase, the present method employed only the solute concentrations in the aqueous phase before and after extraction to determine the partition coefficient. Unlike most previous engineering studies of phenol partitioning in a CO2-water system, the concentrations of phenolic solutes approached infinite dilution in both phases. This makes the results relevant to analytical-scale SFE of environmental water samples with CO2. Because of effective infinite dilution of the solutes, the partition coefficients provide a direct measure of relative CO2-philicity/hydrophilicity of the individual phenols. Compared to the octanol-water partition coefficients of substituted phenols, the CO2-water partition coefficients are more sensitive to substitution in the position neighboring the hydroxyl group. 相似文献
47.
Nearest and reverse nearest neighbor queries for moving objects 总被引:4,自引:0,他引:4
Rimantas Benetis Christian S. Jensen Gytis Karĉiauskas Simonas Ŝaltenis 《The VLDB Journal The International Journal on Very Large Data Bases》2006,15(3):229-249
With the continued proliferation of wireless communications and advances in positioning technologies, algorithms for efficiently
answering queries about large populations of moving objects are gaining interest. This paper proposes algorithms for k nearest and reverse k nearest neighbor queries on the current and anticipated future positions of points moving continuously in the plane. The
former type of query returns k objects nearest to a query object for each time point during a time interval, while the latter returns the objects that have
a specified query object as one of their k closest neighbors, again for each time point during a time interval. In addition, algorithms for so-called persistent and
continuous variants of these queries are provided. The algorithms are based on the indexing of object positions represented
as linear functions of time. The results of empirical performance experiments are reported. 相似文献
48.
Joseph Sam Armijo Piyush Kar Manoranjan Misra 《Nuclear Engineering and Design》2006,236(24):2589-2598
The reference waste package design and operating mode to be used in the Yucca Mountain Repository is reviewed. An alternate (second generation) operating concept and waste package design is proposed to reduce the risk of localized corrosion of waste packages and to reduce repository costs. The second generation waste package design and storage concept is proposed for implementation after the initial licensing and operation of the reference repository design. Implementation of the second generation concept at Yucca Mountain would follow regulatory processes analogous to those used successfully to extend the design life and uprate the power of commercial light water nuclear reactors in the United States. The second generation concept utilizes the benefits of hot dry storage to minimize the potential for localized corrosion of the waste package by liquid electrolytes. The second generation concept permits major reductions in repository costs by increasing the number of fuel assemblies stored in each waste package, by eliminating the need for titanium drip shields and by fabricating the outer container from corrosion resistant low alloy carbon steel. 相似文献
49.
A. Rastelli M. Stoffel G. Katsaros J. Tersoff U. Denker T. Merdzhanova G.S. Kar G. Costantini K. Kern H. von Knel O.G. Schmidt 《Microelectronics Journal》2006,37(12):1471-1476
We report on recent advances in the understanding of surface processes occurring during growth and post-growth annealing of strained islands which may find application as self-assembled quantum dots. We investigate the model system SiGe/Si(0 0 1) by a new approach based on “reading the footprints” which islands leave on the substrate during their growth and evolution. Such footprints consist of trenches carved in the Si substrate. We distinguish between surface footprints and footprints buried below the islands. The former allow us to discriminate islands which are in the process of growing from those which are shrinking. Islands with steep morphologies grow at the expense of smaller and shallower islands, consistent with the kinetics of anomalous coarsening. While shrinking, islands change their shape according to thermodynamic predictions. Buried footprints are investigated by removing the SiGe epilayer by means of selective wet chemical etching. Their reading shows that: (i) during post-growth annealing islands move laterally because of surface-mediated Si–Ge intermixing; (ii) a tree-ring structure of trenches is created by dislocated islands during their “cyclic” growth. This allows us to distinguish coherent from dislocated islands and to establish whether the latter are the result of island coalescence. 相似文献
50.
Bharadwaj Veeravalli Long Chen Hun Yen Kwoon Goh Kar Whee See Ying Lai Lim Peng Hian Ho Chin Chow 《Multimedia Tools and Applications》2006,28(1):89-118
The problem of employing multiple servers to serve a pool of clients on a network based multimedia service is addressed. We
have designed and practically implemented a prototype system employing multiple servers to render a long duration movie to
the customers. We have employed a multiple server retrieval strategy proposed in the literature [39] to realize this system.
In the system, server coordination, client behavior and service facilities are completely controlled by an Agent based approach
in which we have used the recent Jini technology. Several issues, ranging from data retrieval from individual server, behavior
of the underlying network infrastructure, to client management and resource (client buffers) management, are considered in
this implementation. We describe in detail our experiences in this complete design process of every module in the software
architecture, its purpose, and working style. Further, the system is shown to be robust amidst unpredictable failures, i.e.,
in the event of server crashes. The load balancing capability is built-in as a safe guard measure to assure a continuous presentation.
We present a comprehensive discussion on the software architecture to realize this working system and present our experiences.
A system comprising a series of Pentium III PCs on a fast Ethernet network is built as a test-bed. Through this prototype,
a wider scope of research challenges ahead are highlighted as possible extensions.
Bharadwaj Veeravalli Member, IEEE & IEEE-CS, received his BSc in Physics, from Madurai-Kamaraj Uiversity, India in 1987, Master's in Electrical
Communication Engineering from Indian Institute of Science, Bangalore, India in 1991 and PhD from Department of Aerospace
Engineering, Indian Institute of Science, Bangalore, India in 1994. He did his post-doctoral research in the Department of
Computer Science, Concordia University, Montreal, Canada, in 1996. He is currently with the Department of Electrical and Computer
Engineering, Computer and Information Engineering (CIE) division, at The National University of Singapore, Singapore, as a
tenured Associate Professor. His main stream research interests include, Multiprocessor systems, Cluster/Grid computing, Scheduling
in parallel and distributed systems, Bioinformatics & Computational Biology, and Multimedia computing. He is one of the earliest
researchers in the field of divisible load theory. He has published over 75 papers in high-quality International Journals
and Conferences. He had secured several externally funded projects. He has co-authored three research monographs in the areas
of Parallel and Distributed Systems, Distributed Databases, and Multimedia systems, in the years 1996, 2003, and 2005, respectively.
He had guest edited a special issue on Cluster/Grid Computing for IJCA, USA journal in 2004. He has been recently invited
to contribute to Multimedia Encyclopedia, Kluwer Academic Publishers, 2005. He is currently serving the Editorial Board of
IEEE Transactions on Computers, IEEE Transactions on SMC-A and International Journal of Computers & Applications, USA, as an Associate Editor. He had served as a program committee member and as a session chair in several International Conferences.
Long Chen received the B.E. degree in Electrical Engineering and M.E. degree in Electrical Engineering from the Northwestern Polytechnic
University, P. R. China, in 1998 and 2001, respectively, and the M.E. degree in Computer Engineering from the National University
of Singapore, Singapore, in 2004. He is currently a Ph.D. candidate at the Department of Electrical and Computer Engineering,
the University of Delaware, United States. His research interests include multimedia systems, distributed system, network
security, and computer architecture. 相似文献