全文获取类型
收费全文 | 547篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 153篇 |
金属工艺 | 3篇 |
机械仪表 | 10篇 |
建筑科学 | 19篇 |
能源动力 | 13篇 |
轻工业 | 89篇 |
石油天然气 | 1篇 |
无线电 | 30篇 |
一般工业技术 | 111篇 |
冶金工业 | 20篇 |
原子能技术 | 6篇 |
自动化技术 | 114篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 20篇 |
2021年 | 21篇 |
2020年 | 14篇 |
2019年 | 11篇 |
2018年 | 18篇 |
2017年 | 11篇 |
2016年 | 26篇 |
2015年 | 18篇 |
2014年 | 20篇 |
2013年 | 34篇 |
2012年 | 42篇 |
2011年 | 40篇 |
2010年 | 34篇 |
2009年 | 29篇 |
2008年 | 28篇 |
2007年 | 39篇 |
2006年 | 16篇 |
2005年 | 15篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 11篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有579条查询结果,搜索用时 15 毫秒
31.
Giancarlo Fortino Giuseppe Di Fatta Mukaddim Pathan Athanasios V. Vasilakos 《Wireless Networks》2014,20(7):1925-1938
Body area networks (BANs) are emerging as enabling technology for many human-centered application domains such as health-care, sport, fitness, wellness, ergonomics, emergency, safety, security, and sociality. A BAN, which basically consists of wireless wearable sensor nodes usually coordinated by a static or mobile device, is mainly exploited to monitor single assisted livings. Data generated by a BAN can be processed in real-time by the BAN coordinator and/or transmitted to a server-side for online/offline processing and long-term storing. A network of BANs worn by a community of people produces large amount of contextual data that require a scalable and efficient approach for elaboration and storage. Cloud computing can provide a flexible storage and processing infrastructure to perform both online and offline analysis of body sensor data streams. In this paper, we motivate the introduction of Cloud-assisted BANs along with the main challenges that need to be addressed for their development and management. The current state-of-the-art is overviewed and framed according to the main requirements for effective Cloud-assisted BAN architectures. Finally, relevant open research issues in terms of efficiency, scalability, security, interoperability, prototyping, dynamic deployment and management, are discussed. 相似文献
32.
Amédée Djemai Etienne Balan Guillaume Morin Giancarlo Hernandez Jean Claude Labbe Jean Pierre Muller 《Journal of the American Ceramic Society》2001,84(5):1017-1024
Kaolinites with various degrees of structural order and iron content were heated and subsequently analyzed via electron paramagnetic resonance. Iron was present in two different states in the heated materials, either as dilute structural Fe3+ ions or in concentrated Fe3+ phases. During metakaolinization, the environment of dilute Fe3+ ions changed, following modifications of the Al3+ coordination, and the Fe3+ concentration increased. With the breakdown of metakaolinite, the diffusion of Fe3+ ions induced their exsolution in superparamagnetic iron-rich domains (Fe3+ clusters in γ-Al2 O3 and/or Fe3+ oxide nanophases), which produced a decrease in the dilute Fe3+ concentration. The subsequent breakdown of γ-Al2 O3 and the formation of mullite made the dilute Fe3+ concentration increase again, because of the incorporation of Fe3+ ions in the mullite structure. 相似文献
33.
Paola Bonizzoni Gianluca Della Vedova Riccardo Dondi Giancarlo Mauri 《Algorithmica》2010,58(2):282-303
The problem of clustering fingerprint vectors with missing values is an interesting problem in Computational Biology that
has been proposed in Figueroa et al. (J. Comput. Biol. 11(5):887–901, 2004). In this paper we show some improvements in closing the gaps between the known lower bounds and upper bounds on the approximability
of variants of the biological problem. Moreover, we have studied two additional variants of the original problem proposed
in Figueroa et al. (Proc. 11th Computing: The Australasian Theory Symposium (CATS), CRPIT, vol. 41, pp. 57–60, 2005). We prove that all such problems are APX-hard even when each fingerprint contains only two unknown positions and we present
a greedy algorithm that has constant approximation factors for these variants. Despite the hardness of these restricted versions
of the problem, we show that the general clustering problem on an unbounded number of missing values such that they occur
for every fixed position of an input vector in at most one fingerprint is polynomial time solvable. 相似文献
34.
Microbial succession during ripening of Naples-type salami, a southern Italian fermented sausage 总被引:6,自引:0,他引:6
Studies were carried out on the microbiological and physico-chemical changes which occurred during the ripening of five batches of Naples-type salami, manufactured without starter cultures. Salami were sampled internally and externally, and the following microbial groups were studied: lactic acid bacteria, Micrococcaceae and yeasts. The results obtained indicated that lactobacilli constituted the predominant flora, both on the surface and in the interior of the pieces throughout the ripening period. Micrococcaceae and yeasts were also found in considerable number in both locations. Characterisation of 191 lactic isolates indicated that the salami microflora was dominated by homofermentative lactobacilli; approximately 63% of them could be identified as Lactobacillus sake; 40% showing the traits of a racemase negative variant of this species, once referred to Lactobacillus bavaricus. Yeast population mainly comprised Debaryomyces strains. All the colonies grown on mannitol salt and Kranep agar were catalase-positive cocci; novobiocin-resistant staphylococci were the only Micrococcaceae found. The API Staph identification system did not prove to be reliable: 82% of the isolates remained unidentified. To achieve improved characterisation, cluster analysis was subsequently performed on this group, corroborating the existence of a fairly homogeneous group representing an intermediate variety between Staphylococcus xylosus and Staphylococcus saprophyticus that was isolated during the whole ripening process. 相似文献
35.
Giancarlo Razzini 《Journal of power sources》1982,7(3):275-280
The photocatalytic activity of the surface of n-MoSe2 crystals for localized oxidation of iodide ions has been examined in a typical photo-electrochemical cell structure by direct microscopic observation and by output performance measurements under spot illumination.The results demonstrate the presence on the semiconductor surface of ‘active’ and ‘non active’ areas. This drastic difference in the catalytic properties of superficial points in the same semiconductor sample may explain the unique role of the I?, I2 redox couple in the behaviour of layer-type semiconductor photoelectrochemical solar cells, as well as the different response to selective superficial chemical agents presented by layered semiconductor crystals of apparently comparable surface morphology. 相似文献
36.
Rate models are often used to study the behavior of large networks of spiking neurons. Here we propose a procedure to derive rate models that take into account the fluctuations of the input current and firing-rate adaptation, two ubiquitous features in the central nervous system that have been previously overlooked in constructing rate models. The procedure is general and applies to any model of firing unit. As examples, we apply it to the leaky integrate-and-fire (IF) neuron, the leaky IF neuron with reversal potentials, and to the quadratic IF neuron. Two mechanisms of adaptation are considered, one due to an afterhyperpolarization current and the other to an adapting threshold for spike emission. The parameters of these simple models can be tuned to match experimental data obtained from neocortical pyramidal neurons. Finally, we show how the stationary model can be used to predict the time-varying activity of a large population of adapting neurons. 相似文献
37.
38.
De Luca S Ragone R Bracco C Digilio G Aloj L Tesauro D Saviano M Pedone C Morelli G 《Chembiochem : a European journal of chemical biology》2003,4(11):1176-1187
A cyclic CCK8 analogue, cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 (Dpr=L-2,3-diaminopropionic acid), has been designed on the basis of the NMR structure of the bimolecular complex between the N-terminal fragment of the CCK(A) receptor and its natural ligand CCK8. The conformational features of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 have been determined by NMR spectroscopy in aqueous solution and in water containing DPC-d(38) micelles (DPC=dodecylphosphocholine). The structure of the cyclic peptide in aqueous solution is found to be in a relaxed conformation, with the backbone and Dpr29 side chain atoms making a planar ring and the N-terminal tripeptide extending approximately along the plane of this ring. In DPC/water, the cyclic peptide adopts a "boat-shaped" conformation, which is more compact than that found in aqueous solution. The cyclic constraint between the Dpr29 side chain and the CCK8 carboxyl terminus (Lys34) introduces a restriction in the backbone conformational freedom. However, the interaction of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 with the micelles still plays an important role in the stabilisation of the bioactive conformation. A careful comparison of the NMR structure of the cyclic peptide in a DPC micelle aqueous solution with the structure of the rationally designed model underlines that the turn-like conformation in the Trp30-Met31 region is preserved, such that the Trp30 and Met31 side chains can adopt the proper spatial orientation to interact with the CCK(A) receptor. The binding properties of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 to the N-terminal receptor fragment have been investigated by fluorescence spectroscopy in a micellar environment. Estimates of the apparent dissociation constant, K(d), were in the range of 70-150 nM, with a mean value of 120+/-27 nM. Preliminary nuclear medicine studies on cell lines transfected with the CCK(A) receptor indicate that the sulfated-Tyr derivative of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 displaces the natural ligand with an IC(50) value of 15 microM. 相似文献
39.
The two-dimensional suffix tree of an n × n square matrix A is a compacted trie that represents all square submatrices of
A[11]. For the off-line case, i.e., A is given in advance to the algorithm, it is known how to build it in optimal time, for
any type of alphabet size [11],[18]. Motivated by applications in Image Compression[22[, Giancarlo and Guaiana [14] considered
the on-line version of the two-dimensional suffix tree and presented an O(n2 log2 n)-time algorithm, which we refer to as GG. That algorithm is a nontrivial generalization of Ukkonen's on-line algorithm
for standard suffix trees [23]. The main contribution in this paper is an O(log n) factor improvement in the time complexity
of the GG algorithm, making it optimal for unbounded alphabets [9]. Moreover, the ideas presented here also lead to a major
simplification of the GG algorithm. Technically, we are able to preserve most of the structure of the original GG algorithm,
by reducing a computational bottleneck to a primitive operation, i.e., comparison of Lcharacters, which is here implemented
in constant time rather than O(log n) time as in GG. However, preserving that structure comes at a price. Indeed, in order
to make everything work, we need a careful reorganization of another fundamental algorithm: Weiner's algorithm for the construction
of standard suffix trees [24]. Specifically, here we provide a version of that algorithm which takes linear time and works
on-line and concurrently over a set of strings. 相似文献
40.
Tommaso Del Rosso Giancarlo Margheri Stefano Sottini Silvana Trigari Marco De Sario Francesco Prudenzano Daniela Grando 《IEEE sensors journal》2007,7(3):417-425
Optical thermometers have been widely investigated. Here, the temperature behavior of second harmonic generation (SHG) in periodically poled lithium niobate (PPLN) substrates is analyzed; indeed, the QPM tuning in PPLN devices and the obtained SHG efficiency depend on the crystal thermal expansion and dispersion, particularly in the case of guided propagation. Therefore, such devices are suitable to realize optical thermometers for demanding applications. This investigation originated with the request of a thermometer to be installed on the pantographs of high-speed trains. Therefore, it must be sturdy and reliable, but it has even to work in an EMD environment. The temperature behavior of the SHG was theoretically modeled and experimentally validated at 1550 nm, in both bulk propagation and APE channel waveguides. In the first case, by using a 10-mW source, which was obtained from a laser diode and a fiber amplifier, an accuracy of 0.3 degC was found. The pump power was about three orders of magnitude smaller in guided propagation. In view of testing on the trains, our investigation resulted in the design of a device without mechanical contacts with the input and output fibers. Since it works in free propagation, there are no serious alignment and packaging problems. The performances, which are expected to be the same of our tests, widely satisfy all the requirements for working effectively in a strongly hostile and EMD environment and for giving accurate measurements on a wide range of temperatures 相似文献