全文获取类型
收费全文 | 47866篇 |
免费 | 3194篇 |
国内免费 | 1103篇 |
专业分类
电工技术 | 578篇 |
综合类 | 6476篇 |
化学工业 | 3435篇 |
金属工艺 | 2480篇 |
机械仪表 | 817篇 |
建筑科学 | 25892篇 |
矿业工程 | 934篇 |
能源动力 | 530篇 |
轻工业 | 557篇 |
水利工程 | 4805篇 |
石油天然气 | 177篇 |
武器工业 | 154篇 |
无线电 | 146篇 |
一般工业技术 | 3255篇 |
冶金工业 | 1459篇 |
原子能技术 | 75篇 |
自动化技术 | 393篇 |
出版年
2024年 | 123篇 |
2023年 | 317篇 |
2022年 | 907篇 |
2021年 | 1054篇 |
2020年 | 1089篇 |
2019年 | 703篇 |
2018年 | 838篇 |
2017年 | 1102篇 |
2016年 | 1229篇 |
2015年 | 1511篇 |
2014年 | 3129篇 |
2013年 | 2124篇 |
2012年 | 3346篇 |
2011年 | 3633篇 |
2010年 | 2876篇 |
2009年 | 3529篇 |
2008年 | 3352篇 |
2007年 | 4005篇 |
2006年 | 3273篇 |
2005年 | 2831篇 |
2004年 | 2096篇 |
2003年 | 1882篇 |
2002年 | 1633篇 |
2001年 | 1307篇 |
2000年 | 1091篇 |
1999年 | 817篇 |
1998年 | 531篇 |
1997年 | 451篇 |
1996年 | 343篇 |
1995年 | 253篇 |
1994年 | 211篇 |
1993年 | 144篇 |
1992年 | 118篇 |
1991年 | 77篇 |
1990年 | 56篇 |
1989年 | 47篇 |
1988年 | 34篇 |
1987年 | 27篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1980年 | 24篇 |
1979年 | 2篇 |
1975年 | 2篇 |
1967年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
The main subject of this paper is to demonstrate the response of structural concrete to different imposed strain rates. Attention is focused on the strain rate about 10-2 s -1>, where some technical difficulties are experienced when an exact determination of mechanical properties for quasi-brittle materials is attempted. The design of a measurement system, which realizes computer acquisition, analysis, and graphic representation of data, is also presented. 相似文献
24.
25.
Different qualities of concrete have been fire tested using different geometries of the specimens as well as different load levels and load configurations. The main objective with the study was to examine a test methodology consisting of a full‐scale test and different small scale‐tests for determining the probability of spalling and the amount of spalling of fire exposed concrete structures. A reference specimen was defined as a one‐sided fire exposed slab with the dimensions 1800 × 1200 mm2 giving an exposed area of 1500 × 1200 mm2. A number of concrete qualities with different probabilities for spalling, were tested using the reference specimen. These tests showed that the reference specimens worked well giving the expected test results. Small specimens were manufactured in different shapes with the same concrete as the one used in the reference tests. These small specimens were tested either at the same time as the reference specimens in the large furnace or afterwards on a small‐scale furnace where the fire exposed surface was 450 × 360 mm2. The test results clearly show the increased probability and the increased amount of spalling by using external compressive loading. The results also show that by using pre‐stress through bars or wires the load can be lost due to heating of the bars/wires which results in a decreased amount of spalling. The boundary of the specimen also affects the amount of spalling. The spalling around the edges was in all tests less than the spalling on the central parts of the exposed area. It could also be noted that the spalling did not pass completely through any of the specimens. The reason for this is probably that the water/vapour could migrate out from the unexposed surface of the specimen. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
26.
An incremental iterative process based on direct energy minimization is presented for a limit analysis of nonlinear elastic lateral displacements and twists of reinforced and prestressed beams. Problems encountered with the constitutive relations are discussed and two possible material models are presented. 相似文献
27.
In wintertime, the use of studded tyres is common in the Nordic countries, steeply in creasing road wear. Apart from reducing surface quality and durability, the airborne dust presents a potential health hazard. To reduce road wear and dust release, there is a tendency to use harder and more wear-resistant aggregate materials.On the roads in and around Trondheim, mid-Norway, three types of aggregate material are common: greenstone, jasper and ‘mylonite’, in fact a cataclasite. Extensive laboratory testing suggests that cataclasite aggregate has better wear resistance than greenstone, but less than jasper [Erichsen E, Schiellerup H, Gautneb, H, Ottesen RT, Broekmans M. Road dust in Trondheim — analysis of the mineral content of airborne dust. (In Norwegian.) Geological Survey of Norway, NGU-report 2004. 037; 2004. p. 73]. However , observations on fluorescence-impregnated plane and thin sections demonstrate that in practice, cataclasite wears faster than greenstone, which may be attributed to its oriented fabric, as opposed to the random fabric in greenstone and jasper. The original article by Rosiwal from 1896 [Rosiwal A. Neue Untersuchungser gebnisse über die Härte von Mineralien und Gesteine. Verhandlungen der kaiserlich-königlichen geologischen Reichsanstalt, vol. 17/18; 1896. p. 475–491] on abrasion hardness and anisotropy provides an elegant explanation for the field observations. 相似文献
28.
冲切成槽法施工薄壁砼防渗墙,是一种新型防渗墙施工方法,它是利用特制的扁钻头对风化基岩或卵石层进行冲切成槽的施工方法,在工艺上有着较强的优越性. 相似文献
29.
混凝土输送泵的常见故障及排除 总被引:1,自引:0,他引:1
介绍了混凝土输送泵的常见故障,阐述了混凝土输送泵墙管的排除方法,指出只有认真分析造成故障的各种原因,才能按照先外后内、先易后难的原则进行故障处理。 相似文献
30.