全文获取类型
收费全文 | 45577篇 |
免费 | 5579篇 |
国内免费 | 4142篇 |
专业分类
电工技术 | 5247篇 |
技术理论 | 2篇 |
综合类 | 7142篇 |
化学工业 | 2868篇 |
金属工艺 | 1682篇 |
机械仪表 | 2920篇 |
建筑科学 | 2795篇 |
矿业工程 | 852篇 |
能源动力 | 1260篇 |
轻工业 | 2484篇 |
水利工程 | 1081篇 |
石油天然气 | 1270篇 |
武器工业 | 528篇 |
无线电 | 6393篇 |
一般工业技术 | 4559篇 |
冶金工业 | 986篇 |
原子能技术 | 549篇 |
自动化技术 | 12680篇 |
出版年
2024年 | 209篇 |
2023年 | 659篇 |
2022年 | 1133篇 |
2021年 | 1229篇 |
2020年 | 1318篇 |
2019年 | 1214篇 |
2018年 | 1217篇 |
2017年 | 1496篇 |
2016年 | 1628篇 |
2015年 | 1683篇 |
2014年 | 2456篇 |
2013年 | 2704篇 |
2012年 | 3175篇 |
2011年 | 3547篇 |
2010年 | 2761篇 |
2009年 | 2923篇 |
2008年 | 3034篇 |
2007年 | 3456篇 |
2006年 | 3063篇 |
2005年 | 2627篇 |
2004年 | 2269篇 |
2003年 | 1862篇 |
2002年 | 1557篇 |
2001年 | 1300篇 |
2000年 | 1142篇 |
1999年 | 942篇 |
1998年 | 763篇 |
1997年 | 667篇 |
1996年 | 587篇 |
1995年 | 529篇 |
1994年 | 453篇 |
1993年 | 330篇 |
1992年 | 298篇 |
1991年 | 239篇 |
1990年 | 209篇 |
1989年 | 182篇 |
1988年 | 123篇 |
1987年 | 77篇 |
1986年 | 39篇 |
1985年 | 35篇 |
1984年 | 27篇 |
1983年 | 33篇 |
1982年 | 24篇 |
1981年 | 12篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1965年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
31.
A method is considered to solve a conditional optimization problem with a linear-fractional objective function over permutations.
The performance of sub algorithms to solve this problem is evaluated. The practical efficiency of the algorithm is analyzed
by conducting numerical experiments.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 4, pp. 133–146, July–August 2007. 相似文献
32.
We propose a general modeling framework to evaluate the performance of cache consistency algorithms. In addition to the usual hit rate, we introduce the hit* rate as a consistency measure, which captures the fraction of non-stale downloads from the cache. We apply these ideas to the analysis of the fixed TTL consistency algorithm in the presence of network delays. The hit and hit* rates are evaluated when requests and updates are modeled by renewal processes. Classical results on the renewal function lead to various bounds. 相似文献
33.
The breakdown processes of oil films under quasi-static loading have been investigated by using a newly developed steel-oil-mercury system. The relationship between the thickness and breakdown ratio of a hexadecane film is represented by a single master curve independently of the indentation speed, indentation load, and temperature. The master curve shows that the breakdown process of hexadecane includes two stages; one is the decrement of the thickness without breakdown and the other is the decrement of the thickness with a drastic progress of breakdown. By solving a small amount of fatty acid in hexadecane, the thickness increases and the breakdown ratio decreases noticeably; a multilayer residual film supporting normal load is formed between two metal surfaces. Experiments at different temperatures reveal a negative relationship between the temperature and thickness of residual film, which indicates that the residual film is organized by physical interaction rather than chemical interaction. At least under a lower concentration, the residual film appears to consist of not only fatty acid molecules but also hexadecane molecules. 相似文献
34.
L. M. CRUZ-ORIVE 《Journal of microscopy》2005,219(1):18-28
A new principle is presented to generate isotropic uniform random (IUR) test lines hitting a geometric structure in three-dimensional space (3D). The principle therefore concerns the estimation of surface area, volume, membrane thickness, etc., of arbitrary structures with piecewise smooth boundary. The principle states that a point-sampled test line on an isotropic plane through a fixed point in 3D is effectively an invariant test line in 3D. Particular attention is devoted to the stereology of particles, where an alternative to the surfactor method is obtained to estimate surface area. An interesting case arises when the particle is convex. The methods are illustrated with synthetic examples. 相似文献
35.
Gabriel Nivasch 《Information Processing Letters》2004,90(3):135-140
We present an algorithm for detecting periodicity in sequences produced by repeated application of a given function. Our algorithm uses logarithmic memory with high probability, runs in linear time, and is guaranteed to stop within the second loop through the cycle. We also present a partitioning technique that offers a time/memory tradeoff. Our algorithm is especially well suited for sequences where the cycle length is typically small compared to the length of the acyclic prefix. 相似文献
36.
37.
38.
Chouping Luo Marek Klisinski 《International journal for numerical methods in engineering》2004,61(2):159-188
The present study is a continuation of our previous work with the aim to reduce problems caused by standard higher order elements in contact problems. The difficulties can be attributed to the inherent property of the Galerkin method which gives uneven distributions of nodal forces resulting in oscillating contact pressures. The proposed remedy is use of piece‐wise linear weight functions. The methods to establish stiffness and/or mass matrix for 8‐node quadrilateral element in 2D are presented, i.e. the condensing and direct procedures. The energy and nodal displacement error norms are also checked to establish the convergence ratio. Interpretation of calculated contact pressures is discussed. Two new 2D 8‐node quadrilateral elements, QUAD8C and QUAD8D, are derived and tested in many examples, which show their good performance in contact problems. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
39.
40.
We introduce a new probabilistic approach to dealing with uncertainty, based on the observation that probability theory does not require that every event be assigned a probability. For a nonmeasurable event (one to which we do not assign a probability), we can talk about only the inner measure and outer measure of the event. In addition to removing the requirement that every event be assigned a probability, our approach circumvents other criticisms of probability-based approaches to uncertainty. For example, the measure of belief in an event turns out to be represented by an interval (defined by the inner and outer measures), rather than by a single number. Further, this approach allows us to assign a belief (inner measure) to an event E without committing to a belief about its negation -E (since the inner measure of an event plus the inner measure of its negation is not necessarily one). Interestingly enough, inner measures induced by probability measures turn out to correspond in a precise sense to Dempster-Shafer belief functions. Hence, in addition to providing promising new conceptual tools for dealing with uncertainty, our approach shows that a key part of the important Dempster-Shafer theory of evidence is firmly rooted in classical probability theory. Cet article présente une nouvelle approche probabiliste en ce qui concerne le traitement de l'incertitude; celle-ci est basée sur l'observation que la théorie des probabilityés n'exige pas qu'une probabilityé soit assignée à chaque événement. Dans le cas d'un événement non mesurable (un événement pour lequel on n'assigne aucune probabilityé), nous ne pouvons discuter que de la mesure intérieure et de la mesure extérieure de l'évenément. En plus d'éliminer la nécessité d'assigner une probabilityéà l'événement, cette nouvelle approche apporte une réponse aux autres critiques des approches à l'incertitude basées sur des probabilityés. Par exemple, la mesure de croyance dans un événement est représentée par un intervalle (défini par la mesure intérieure et extérieure) plutǒt que par un nombre unique. De plus, cette approche nous permet d'assigner une croyance (mesure intérieure) à un événement E sans se compromettre vers une croyance à propos de sa négation -E (puisque la mesure intérieure d'un événement et la mesure intérieure de sa négation ne sont pas nécessairement une seule et unique mesure). II est intéressant de noter que les mesures intérieures qui résultent des mesures de probabilityé correspondent d'une manière précise aux fonctions de croyance de Dempster-Shafer. En plus de constituer un nouvel outil conceptuel prometteur dans le traitement de l'incertitude, cette approche démontre qu'une partie importante de la théorie de l'évidence de Dempster-Shafer est fermement ancrée dans la theorie classique des probabilityés. 相似文献