全文获取类型
收费全文 | 20054篇 |
免费 | 2404篇 |
国内免费 | 1097篇 |
专业分类
电工技术 | 4239篇 |
综合类 | 1770篇 |
化学工业 | 1611篇 |
金属工艺 | 796篇 |
机械仪表 | 969篇 |
建筑科学 | 1413篇 |
矿业工程 | 310篇 |
能源动力 | 2427篇 |
轻工业 | 481篇 |
水利工程 | 389篇 |
石油天然气 | 562篇 |
武器工业 | 111篇 |
无线电 | 2791篇 |
一般工业技术 | 2235篇 |
冶金工业 | 551篇 |
原子能技术 | 388篇 |
自动化技术 | 2512篇 |
出版年
2024年 | 61篇 |
2023年 | 317篇 |
2022年 | 586篇 |
2021年 | 743篇 |
2020年 | 762篇 |
2019年 | 684篇 |
2018年 | 615篇 |
2017年 | 818篇 |
2016年 | 889篇 |
2015年 | 837篇 |
2014年 | 1338篇 |
2013年 | 1345篇 |
2012年 | 1416篇 |
2011年 | 1647篇 |
2010年 | 1141篇 |
2009年 | 1194篇 |
2008年 | 1101篇 |
2007年 | 1257篇 |
2006年 | 1108篇 |
2005年 | 973篇 |
2004年 | 793篇 |
2003年 | 673篇 |
2002年 | 612篇 |
2001年 | 505篇 |
2000年 | 391篇 |
1999年 | 329篇 |
1998年 | 234篇 |
1997年 | 212篇 |
1996年 | 195篇 |
1995年 | 165篇 |
1994年 | 127篇 |
1993年 | 91篇 |
1992年 | 71篇 |
1991年 | 58篇 |
1990年 | 43篇 |
1989年 | 51篇 |
1988年 | 28篇 |
1987年 | 27篇 |
1986年 | 18篇 |
1985年 | 17篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 18篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In this paper, the average stress method for the fatigue limit evaluation of stress raising geometrical features is revised and extended. In particular, an analytical close‐form approach was used and the linear elastic stress equations were modified by taking into account the effect of nominal stress on the local stress distribution. Hence, the average tangential stress was correctly evaluated over a distance of 2a0, where a0 was El Haddad's short crack constant, for long and small notches as well as for crack‐like notches. When this model is applied to a wide range of geometrical features subjected to mode I fatigue loading, the classical shape of the curves of the Kitagawa–Takahashi diagram was obtained for changes in crack‐like notch size. Similarly, notch sensitivity was estimated by reducing the notch tip radius. The accuracy of the proposed method in predicting fatigue limits was then checked by using experimental data taken from the literature and generated on testing specimens weakened by rounded and sharp notches as well as by small artificial defects. 相似文献
32.
SOPHO-S系列数字程控交换机是由飞利蒲公司生产的。本文分析了该系列交换机的总体结构,并了它的线路传输技术。 相似文献
33.
34.
In this paper,a sequential algorithm computing the aww vertex pair distance matrix D and the path matrix Pis given.On a PRAM EREW model with p,1≤p≤n^2,processors,a parallel version of the sequential algorithm is shown.This method can also be used to get a parallel algorithm to compute transitive closure array A^* of an undirected graph.The time complexity of the parallel algorithm is O(n^3/p).If D,P and A^* are known,it is shown that the problems to find all connected components,to compute the diameter of an undirected graph,to determine the center of a directed graph and to search for a directed cycle with the minimum(maximum)length in a directed graph can all be solved in O(n^2/p logp)time. 相似文献
35.
36.
The switchable optical properties of Pd-protected RCo2-type Ho0.6Mm0.4Co2 alloy thin films have been investigated in a KOH electrolyte. The reversible optical switching has been carried out simultaneously by measuring transmitted light through the thin film during electrochemical charging–discharging of hydrogen. The dependence of switching speed and cyclic durability of the film on the charging and discharging current density as well as concentration of KOH electrolyte has been studied. In addition, cyclic voltammetric measurements have been performed to examine the hydride formation and decomposition reactions. 相似文献
37.
Hydroprocessing catalysts based on Ni, Co, Mo and W are used in various refinery processing applications where several deactivation mechanisms become of importance (coke formation, active phase sintering, metals deposition, poisoning) in the catalyst's life cycle. The life cycle of commercial hydroprocessing catalysts is very complex and includes the catalyst production, sulfidation, use, oxidative regeneration followed by re-sulfidation and reuse or, if reuse is not possible, recycling or disposal. To understand the changes in catalyst properties taking place during a life cycle, the catalyst quality in the different stages can be best monitored by using advanced analytical techniques. The catalyst's life cycle is further complicated by numerous technical, environmental and organizational issues involved. In principle, different companies can be involved in each of the life cycle steps. Leading catalyst manufacturers, together with specialized firms, offer refineries a total catalyst management concept, starting with the purchase of the fresh catalyst and ending with its final recycling or disposal. Total catalyst management includes a broad range of services, ensuring optimal timing during the change-out process, reliable, smooth and safe operations, minimal downtime and maximum catalyst and unit performance. 相似文献
38.
High crude oil prices and pollution problems have drawn attention to alternative vehicle technologies and fuels for the transportation sector. The question is: What are the benefits/costs of these technologies for society? To answer this question in a quantitative way, a web-based model (http://vehiclesandfuels.memebot.com) has been developed to calculate the societal life cycle costs, the consumer life cycle costs and the tax for different vehicle technologies. By comparing these costs it is possible to draw conclusions about the social benefit and the related tax structure. The model should help to guide decisions toward optimality, which refers to maximum social benefit. The model was applied to the case of Thailand. The life cycle cost of 13 different alternative vehicle technologies in Thailand have been calculated and the tax structure analyzed. 相似文献
39.
Ahmadreza Momeni Amir G. Aghdam 《International Journal of Adaptive Control and Signal Processing》2007,21(10):885-910
Most of the existing switching control techniques are developed specifically for finite-dimensional linear time-invariant (LTI) systems. In many practical applications, however, it is essential to take time delay into consideration in the modelling as the control system can be highly sensitive to delay. In this paper, a multi-model switching control algorithm is proposed for retarded time-delay systems. It is assumed that the plant is represented by a family of known multi-input multi-output, observable, LTI models with multiple delays in the states, and that corresponding to each model in the known family, there exists a high-performance finite-dimensional LTI controller. In addition, it is supposed that a bound on the magnitude of the external inputs and disturbances is available. It is then shown that the proposed switching controller can stabilize the uncertain system, and that under some mild conditions, output tracking can be achieved in the given problem setting. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
40.
Four experiments investigated the effect of recent selective practice on the cost of switching between 2 tasks afforded by letter-digit pairs: alphabet arithmetic and shape comparison. Experiments 1 and 2 found a greater cost associated with switching to the more recently practiced task: evidence that task-set inertia contributes to switching costs. Experiment 3 found this effect to be limited to trials on which a recently trained stimulus followed another such stimulus: a result problematic for all current theories of task-set priming. Experiment 4 showed that the effect of recent practice was eliminated by active preparation for a task switch: It appears that endogenous task-set preparation reduces the effects of task-set inertia. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献