全文获取类型
收费全文 | 6380篇 |
免费 | 350篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 103篇 |
综合类 | 21篇 |
化学工业 | 1338篇 |
金属工艺 | 131篇 |
机械仪表 | 122篇 |
建筑科学 | 365篇 |
矿业工程 | 29篇 |
能源动力 | 143篇 |
轻工业 | 642篇 |
水利工程 | 48篇 |
石油天然气 | 9篇 |
无线电 | 510篇 |
一般工业技术 | 1165篇 |
冶金工业 | 1044篇 |
原子能技术 | 50篇 |
自动化技术 | 1014篇 |
出版年
2023年 | 66篇 |
2022年 | 118篇 |
2021年 | 183篇 |
2020年 | 137篇 |
2019年 | 126篇 |
2018年 | 144篇 |
2017年 | 143篇 |
2016年 | 209篇 |
2015年 | 204篇 |
2014年 | 240篇 |
2013年 | 331篇 |
2012年 | 311篇 |
2011年 | 401篇 |
2010年 | 339篇 |
2009年 | 281篇 |
2008年 | 300篇 |
2007年 | 295篇 |
2006年 | 213篇 |
2005年 | 214篇 |
2004年 | 151篇 |
2003年 | 146篇 |
2002年 | 136篇 |
2001年 | 97篇 |
2000年 | 94篇 |
1999年 | 121篇 |
1998年 | 241篇 |
1997年 | 162篇 |
1996年 | 159篇 |
1995年 | 114篇 |
1994年 | 83篇 |
1993年 | 90篇 |
1992年 | 50篇 |
1991年 | 36篇 |
1990年 | 40篇 |
1989年 | 38篇 |
1988年 | 28篇 |
1987年 | 25篇 |
1986年 | 37篇 |
1985年 | 47篇 |
1984年 | 31篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1979年 | 22篇 |
1978年 | 22篇 |
1977年 | 44篇 |
1976年 | 48篇 |
1975年 | 26篇 |
1972年 | 29篇 |
1971年 | 22篇 |
1970年 | 28篇 |
排序方式: 共有6734条查询结果,搜索用时 31 毫秒
121.
Max-SAT-CC is the following optimization problem: Given a formula in CNF and a bound k, find an assignment with at most k variables being set to true that maximizes the number of satisfied clauses among all such assignments. If each clause is restricted to have at most ? literals, we obtain the problem Max-?SAT-CC. Sviridenko [Algorithmica 30 (3) (2001) 398-405] designed a (1−e−1)-approximation algorithm for Max-SAT-CC. This result is tight unless P=NP [U. Feige, J. ACM 45 (4) (1998) 634-652]. Sviridenko asked if it is possible to achieve a better approximation ratio in the case of Max-?SAT-CC. We answer this question in the affirmative by presenting a randomized approximation algorithm whose approximation ratio is . To do this, we develop a general technique for adding a cardinality constraint to certain integer programs. Our algorithm can be derandomized using pairwise independent random variables with small probability space. 相似文献
122.
Numerous single-unit recording studies have found mammalian hippocampal neurons that fire selectively for the animal's location in space, independent of its orientation. The population of such neurons, commonly known as place cells, is thought to maintain an allocentric, or orientation-independent, internal representation of the animal's location in space, as well as mediating long-term storage of spatial memories. The fact that spatial information from the environment must reach the brain via sensory receptors in an inherently egocentric, or viewpoint-dependent, fashion leads to the question of how the brain learns to transform egocentric sensory representations into allocentric ones for long-term memory storage. Additionally, if these long-term memory representations of space are to be useful in guiding motor behavior, then the reverse transformation, from allocentric to egocentric coordinates, must also be learned. We propose that orientation-invariant representations can be learned by neural circuits that follow two learning principles: minimization of reconstruction error and maximization of representational temporal inertia. Two different neural network models are presented that adhere to these learning principles, the first by direct optimization through gradient descent and the second using a more biologically realistic circuit based on the restricted Boltzmann machine (Hinton, 2002; Smolensky, 1986). Both models lead to orientation-invariant representations, with the latter demonstrating place-cell-like responses when trained on a linear track environment. 相似文献
123.
Dr. Jan U. Becker Prof. Dr. Michel Clement Dipl.-Kffr. Ute Schaedel 《WIRTSCHAFTSINFORMATIK》2008,50(6):482-488
Shared WiFi-Communities emerge when users share their private Wireless Fidelity with others and in return get free internet access via community members’ internet connection. Supply of wireless capacity and demand for WLAN usually are coordinated by a central authority therewith users can find specific hosts within the community. Initial players that conduct commercial WiFi-Communities established their position in the market. The international market leader with 170,000 hotspots worldwide is FON. The commercial success of shared WiFi-communities (e.g. FON) depends on the adoption of a special router or modifications of the existing WLAN-infrastructure. More importantly it is essential that users permanently offer broadband capacity to the community. Only then net effects can durably generate enhanced usage benefits. A survey of 268 German FON users reveals that the community shows a high level of cohesion. Users barely vary from the default setting concerning shared bandwidth of the router. Additionally most interviewees offer their WLAN 24 hours a day. Despite the possibility of earning money with the wireless capacity most users do not offer bandwidth with a purely economic ambition. Although the market potential of shared WiFi communities appears tremendous legal obstructions and technical restraints exacerbate penetration. 相似文献
124.
Markus Hinkelmann Andreas Jakoby and Peer Stechert Institut für Theoretische Informatik Universitt zu Lübeck Germany Fachgruppe Didaktik der Informatik und E-Learning Universitt Siegen Germany 《计算机科学技术学报》2008,23(5)
In most of the auction systems the values of bids are known to the auctioneer. This allows him to manipulate the outcome of the auction. Hence, one might be interested in hiding these values. Some cryptographically secure protocols for electronic auctions have been presented in the last decade. Our work extends these protocols in several ways. On the basis of garbled circuits, i.e., encrypted circuits, we present protocols for sealed-bid auctions that fulfill the following requirements: 1) protocols are information-theoretically t-private for honest but curious parties; 2) the number of bits that can be learned by malicious adversaries is bounded by the output length of the auction; 3) the computational requirements for participating parties are very low: only random bit choices and bitwise computation of the XOR-function are necessary. Note that one can distinguish between the protocol that generates a garbled circuit for an auction and the protocol to evaluate the auction. In this paper we address both problems. We will present a t-private protocol for the construction of a garbled circuit that reaches the lower bound of 2t 1 parties, and a more randomness effcient protocol for (t 1)2 parties. Finally, we address the problem of bid changes in an auction. 相似文献
125.
Michael E. Becker 《Journal of the Society for Information Display》2009,17(3):229-238
Abstract— A method for evaluation of the contrast of moving step‐grating patterns under smooth‐pursuit eye‐tracking conditions without imaging data acquisition and image analysis is introduced. Periodic optical responses of the display to a set of simple driving signals have been recorded at a fixed location, and the luminance vs. time data has been evaluated to obtain two types of contrast for characterization of the dynamical performance of the display under test: the frame‐convoluted contrast and the frame‐integrated contrast. The relation of this characterization with respect to modulation transfer functions from impulse responses and to the dynamic modulation transfer function from sine‐gratings is explained and discussed. The approach described here provides a detailed and comprehensive characterization of the dynamical properties of electronic displays including both extreme cases of step‐response and impulse‐response with quantities that are related to visual perception. With this type of evaluation, the visual resolution of displays can be described by the same characteristics in the static and the dynamic case. The method is attractive due to limited instrumental efforts and the transparent method of evaluation. 相似文献
126.
van Oostrum J Calonder C Rechsteiner D Ehrat M Mestan J Fabbro D Voshol H 《Proteomics. Clinical applications》2009,3(4):412-422
Controlling aberrant protein kinase activity is a promising strategy for a variety of diseases, particularly cancer. Hence, the development of kinase inhibitors is currently a focal point for pharmaceutical research. In this study we utilize a chip-based reverse phase protein array (RPA) platform for profiling of kinase inhibitors in cell-based assays. In combination with the planar wave-guide technology the assay system has an absolute LOD down to the low zeptomole range. A431 cell lysates were analyzed for the activation state of key effectors in the epidermal growth factor (EGF) and insulin signaling pathways to validate this model for compound screening. A microtiter-plate format for growing, treating, and lysing cells was shown to be suitable for this approach, establishing the value of the technology as a screening tool for characterization of large numbers of kinase inhibitors against a wide variety of cellular signaling pathways. Moreover, the reverse array format allows rapid development of site-specific phosphorylation assays, since in contrast to ELISA type systems only a single antigen-specific antibody is required. 相似文献
127.
Ludovit Markus 《Journal of Intelligent and Robotic Systems》1994,11(1-2):109-116
A general method for solving the robot inverse kinematics problem is presented. The method is based upon the general elimination method to obtain the equivalent system of equations which are triangularized and the solutions of the inverse kinematics problem can be solved by backsubstitutions. 相似文献
128.
Hemminki Ari; Hoffren Anna-Marja; Takkinen Kristiina; Vehniainen Markus; Makinen Maija-Liisa; Pettersson Kim; Teleman Olle; Soderlund Hans; Teeri Tuula T. 《Protein engineering, design & selection : PEDS》1995,8(2):185-191
Europium chelates provide a non-radioactive alternative forsensitive labelling of antibodies for diagnostic immunoassays.Lysine residues at antibody surfaces are ready targets for labellingby an isothiocyanate derivative of the europium chelate (Eu3+).Here the labelling efficiency of a recombinant anti-human -fetoprotein(hAFP) Fab fragment has been improved by increasing its lysinecontent by protein engineering. Molecular modelling was usedto identify three light chain constant domain surface arginineresidues, R154, R187 and R210, which were mutated to lysineresidues. The mutations did not influence the affinity of thelysine-enriched Fab fragment and its labelling efficiency wasfound to be 40% higher than that of the wildtype Fab fragmentWith low degree of labelling, the affinities of the two Fabfragments were identical and comparable with that of the originalmonoclonal anti-hAFP IgG. With a higher degree of labellingthe affinities of both Fab fragments decreased more than thatof the intact IgG since more lysine residues are available forlabelling in the additional heavy chain constant domains ofthe larger molecule. Electrostatic adsorption and covalent immobilizationof the Fab fragments were characterized by BIAcoreTM and thelysine-enriched Fab fragment was found to be more efficientlyimmobilized to an activated carboxymethyl surface. 相似文献
129.
Erik Valentine Bachtiar Markus Rüggeberg Stefan Hering Michael Kaliske Peter Niemz 《Materials and Structures》2017,50(6):248
In this study, several theoretical models to numerically estimate shear properties of orthotropic materials are introduced. These approaches are based on the combination of Hankinson’s empirically derived formula with other empirical and analytical calculations. Next to shear moduli, which are estimated from the elastic moduli and Poisson’s ratios, shear strengths are also estimated from the in-axis strengths. The models are validated by mechanical tests on walnut wood (Juglans regia L.), for which a sufficient data set can be found in literature. The Arcan test is used to estimate the shear moduli, while the shear block test is used to estimate the shear strengths. The results show that the model, which is based on a combined use of Hankinson’s formula and tensor rotation, gives the best estimation of shear moduli as evaluated by the minimum differences to the experimentally obtained results. For the shear strengths, a combination of Hankinson’s formula and Norris’ failure criterion shows the best agreement in comparison to the experimental data. The theoretical calculations may be used for a time efficient estimation of shear modulus and strength in comparison to the very time-consuming experimental estimation. 相似文献