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排序方式: 共有1894条查询结果,搜索用时 15 毫秒
921.
A numerical study of methods to predict the capacity of multiple steel-timber dowel joints 总被引:2,自引:1,他引:1
In this study, two numerical methods are used to predict the load-bearing capacity of multiple steel-timber dowel joints loaded parallel to the grain. The aim was to show the possibility and the advantages of using numerical methods when designing multiple dowel-type joints. The results showed a good correlation to experimental results taken from the literature and to traditional joint calculations as given in Eurocode 5 (2004). The numerical methods are capable of predicting alternative dowel patterns that can be of great value, not only from a structural point of view, but also for aesthetical reasons. In addition, the numerical methods presented in this study can also be efficient tools for the structural engineer when considering complex loading situations in joints, i.e. in cases involving other loading situations than pure tension parallel to the grain. 相似文献
922.
Johan Hoffman Claes Johnson 《Computer Methods in Applied Mechanics and Engineering》2005,194(1):19-44
In this paper we propose and study a subgrid model for linear convection-diffusion-reaction equations with fractal rough coefficients. The subgrid model is based on scale extrapolation of a modeling residual from coarser scales using a computed solution on a finest scale as reference. We show in experiments that a solution with subgrid model on a scale h in most cases corresponds to a solution without subgrid model on a scale less than h/4. We also present error estimates for the modeling error in terms of modeling residuals. 相似文献
923.
924.
Johan Liu Liqiang Cao Min Xie Thong-Ngee Goh Yong Tang 《Electronics Packaging Manufacturing, IEEE Transactions on》2005,28(4):322-327
In this paper, a generic four-parameter model has been developed and applied to the anisotropic conductive adhesive (ACA) flip-chip joining technology for electronics packaging applications. The model can also be used to predict any minimum failure cycles if the maximum acceptable failure criterion (in this case, a preset electrical resistance value) is set. The original reliability testing from which the test data was obtained was carried out on flip-chip anisotropically conductive adhesive joints on an FR-4 substrate. In the study, nine types of ACA and one nonconductive film (NCF) were used. In total, nearly 1000 single joints were subjected to reliability tests in terms of temperature cycling between -40/spl deg/C and 125/spl deg/C with a dwell time of 15 min and a ramp rate of 110/spl deg/C/min. The reliability was characterized by single contact resistance measured using the four-probe method during temperature cycling testing up to 3000 cycles. A single Weibull model is used for two failure definitions defined as larger than 50 m/spl Omega/ and larger than 100 m/spl Omega/ respectively using the in situ electrical resistance measurement technique. The failure criteria are incorporated into this Weibull model. This paper shows the flexibility and usefulness of Weibull distribution in this type of applications. 相似文献
925.
An experimental and numerical study of the effect of friction in single dowel joints 总被引:4,自引:3,他引:1
The effect of friction between the dowel and the surrounding timber was studied for single dowel-type joints. The joints tested were divided into two groups of joints, where the surface of the dowels differed. For the first group, the dowels had a smooth surface and for the second group the dowels had a rough surface. A contact-free measurement technique was used in the experimental investigation. In addition to that, numerical simulations were carried out aimed at predicting the load-bearing capacity of the joints tested as well as estimating the coefficient of friction between the dowel and the surrounding timber. Important conclusions from this study, which are supported by previous research, are that the load-bearing capacity of single dowel-type joints increases when the surface roughness of the dowel increases. A very small scatter in the results, in terms of the load-displacement behavior, was seen in the tests with rough surface dowels. For the joints with smooth surface dowels, the elastic response as well as the plastic response varied considerably between different tests. The current version of the European timber code EC5 does not explicitly take into account the effect of friction. In order to take the effect into account embedding tests have to be performed in order to be able to consider the benefits of using dowels with rough surface. 相似文献
926.
Johan van Benthem 《Journal of Logic, Language and Information》2005,14(3):263-279
Some initial motivations for the Guarded Fragment still seem of interest in carrying its program further. First, we stress the equivalence between two perspectives: (a) satisfiability on standard models for guarded first-order formulas, and (b) satisfiability on general assignment models for arbitrary first-order formulas. In particular, we give a new straightforward reduction from the former notion to the latter. We also show how a perspective shift to general assignment models provides a new look at the fixed-point extension LFP(FO) of first-order logic, making it decidable. Next, we relate guarded syntax to earlier quantifier restriction strategies for achieving effective axiomatizability in second-order logic – pointing at analogies with ‘persistent’ formulas, which are essentially in the Bounded Fragment of many-sorted first-order logic. Finally, we look at some further unexplored directions, including the systematic use of ‘quasi-models’ as a semantics by itself. 相似文献
927.
比利时高放废物处置库设计及与基岩和工程屏障体系的热-水-力性状的相关研究 总被引:4,自引:1,他引:3
在比利时,泥岩中地质处置是高放废物最终处置的首选,处置库在高放废物与生物圈之间的多重屏障基础上设计的,而Boom泥岩作为基岩的研究已有20多年历史,1980年比利时做出重大决定,建立名为HADES的地下研究机构,以研究Boom泥岩在地下223m处的力学性质,并调查和论证处置的可行性,为处置库屏障(天然和人工)提供可靠数据,在HADES的众多现场试验中很多试验用来对基岩和工程屏障体系(包括封口和回填的可行性)热-水-力性状进行研究,包括CACTUS,ATLAS,BACCHUS和RESEAL等项目。自1995年以来,研究开发计划向大型和示范性试验方向发展。最主要成果是运用工业技术建立地下研究设施(竖井和井巷)可行性得到了验证,且这种工业技术给研究提供一个较好机会,便于进一步认识基岩泥岩(CLIPEX方案)的水-力性状及了解隧道开挖工程(SELFRAC课题)对挖掘破坏区的影响,另一个重大成果是成功地实现对一种称为“OPHELE”的预掉膨润土(人工屏障材料)加热和水化地面大型试验。下一步工作内容包括实现大尺寸现场加热器试验(PRACLAY试验),此试验预计于2006年开始,并可持续10a之久,据此,首先简要描述比利时高效废物处置库设计,然后回顾Boom泥岩和工程屏障体系的热-水-力性状相关试验,最后介绍下一步大规模PRACLAY试验。 相似文献
928.
Bart De Win Riccardo Scandariato Koen Buyens Johan Grégoire Wouter Joosen 《Information and Software Technology》2009,51(7):1152-1171
Development processes for software construction are common knowledge and mainstream practice in most development organizations. Unfortunately, these processes offer little support in order to meet security requirements. Over the years, research efforts have been invested in specific methodologies and techniques for secure software engineering, yet dedicated processes have been proposed only recently.In this paper, three high-profile processes for the development of secure software, namely OWASP’s CLASP, Microsoft’s SDL and McGraw’s Touchpoints, are evaluated and compared in detail. The paper identifies the commonalities, discusses the specificity of each approach, and proposes suggestions for improvement. 相似文献
929.
930.
Johan Vinterbck 《Biomass & bioenergy》2004,27(6):513-520
Large-scale implementation of wood pellets as a solid biomass fuel represents a change in the energy system that will have both economic and environmental consequences. This article represents a summary of a state of the art conference, which was organised in Sweden in September 2002. The aim was to bring together people to create a network where industry, research, other expertise and decision makers meet to build a strong pellet industry for the future. The sum of the economic, technological and environmental evidence presented at this conference weighs very heavily in favour of the pellet option. 相似文献