全文获取类型
收费全文 | 9471篇 |
免费 | 1592篇 |
国内免费 | 974篇 |
专业分类
电工技术 | 499篇 |
综合类 | 1180篇 |
化学工业 | 255篇 |
金属工艺 | 491篇 |
机械仪表 | 807篇 |
建筑科学 | 1321篇 |
矿业工程 | 430篇 |
能源动力 | 183篇 |
轻工业 | 159篇 |
水利工程 | 270篇 |
石油天然气 | 463篇 |
武器工业 | 81篇 |
无线电 | 1510篇 |
一般工业技术 | 1010篇 |
冶金工业 | 305篇 |
原子能技术 | 74篇 |
自动化技术 | 2999篇 |
出版年
2024年 | 34篇 |
2023年 | 209篇 |
2022年 | 428篇 |
2021年 | 472篇 |
2020年 | 471篇 |
2019年 | 318篇 |
2018年 | 249篇 |
2017年 | 333篇 |
2016年 | 344篇 |
2015年 | 416篇 |
2014年 | 635篇 |
2013年 | 578篇 |
2012年 | 819篇 |
2011年 | 877篇 |
2010年 | 694篇 |
2009年 | 707篇 |
2008年 | 662篇 |
2007年 | 686篇 |
2006年 | 565篇 |
2005年 | 490篇 |
2004年 | 385篇 |
2003年 | 347篇 |
2002年 | 257篇 |
2001年 | 194篇 |
2000年 | 164篇 |
1999年 | 150篇 |
1998年 | 117篇 |
1997年 | 82篇 |
1996年 | 76篇 |
1995年 | 58篇 |
1994年 | 48篇 |
1993年 | 37篇 |
1992年 | 19篇 |
1991年 | 12篇 |
1990年 | 23篇 |
1989年 | 16篇 |
1988年 | 13篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1975年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
为了研究组合梁对方钢管混凝土柱-组合梁框架抗连续倒塌性能的影响,设计了带有混凝土现浇楼板方钢管混凝土柱-组合梁框架(CFSTCBF)及不带楼板的方钢管混凝土柱-钢梁框架(CFSTSBF),采用拆除构件法对两个试件的抗连续倒塌性能进行竖向加载试验研究,对其在中柱失效工况下的破坏模式、受力机理以及主要的抗力机制进行分析,同时对现浇混凝土楼板和节点在连续倒塌过程中的性能进行探讨。研究表明:两个试件的破坏均是由正弯矩区钢梁破坏引起,结构的倒塌阶段可分为弹塑性阶段、塑性阶段、过渡阶段和悬链线阶段,压拱机制和悬链线机制均能改善结构的抗倒塌性能;混凝土楼板可以有效增强结构的承载能力,提高结构的初始转动刚度,但在改善结构变形能力方面的作用较弱。 相似文献
42.
浅埋隧道围岩的质量普遍较低,整体稳定性差,隧道震害表明强震作用下浅埋隧道极易发生震动破坏。通过开展V级围岩条件下浅埋隧道在小震下的震动响应和逐级加载下的震动垮塌振动台试验,研究了小震作用下围岩加速度沿地层的分布、衬砌结构的内力变化和围岩内部的水平位移变化规律,强震作用下衬砌结构裂缝开展和围岩震动垮塌。结果表明:围岩加速度随距地表距离的减小而增加,地表加速度约为拱顶处加速度的1.63倍,相同高度平面内靠近隧道的围岩振动具有一定的加强;隧道拱顶围岩内部的水平位移大约是拱腰围岩内部的1.23倍,围岩内部位移随着远离隧道而逐渐减小,随着震动烈度的增加而不断增加;隧道拱顶上方垮塌区形状近似漏斗,震动引起隧道衬砌结构拱脚处的轴力和弯矩变化最大,且拱肩和拱脚处裂缝分布最多,应加强拱肩和拱脚处结构的抗震性能。 相似文献
43.
In this paper, the effect of horizontal bracing on enhancing the resistance of steel moment frames against progressive collapse is investigated. Previously designed 6 bay by 3 bay 18‐story steel frame prototype building with 6 m bay span (namely, unbraced frame), which was susceptible to progressive collapse, is retrofitted by four types of horizontal bracing systems on the perimeter of the topmost story and analyzed using 3D nonlinear dynamic method. Six different cross‐sections for each bracing system type are considered, and the capacity curves for each model are obtained. Three column removal circumstances, namely, Edge Short Column, First Edge Long Column, and Edge Long Column are considered in this paper. The results imply that horizontal bracing would increase the resistance of moment frames against progressive collapse. However, one of the bracing types in which axial compressive force is created in braces is not appropriate for retrofitting. 相似文献
44.
Mark Grigorian Abdolreza S. Moghadam Mozhgan Kamizi 《The Structural Design of Tall and Special Buildings》2019,28(7)
Performance‐based seismic design, as an alternative to conventional methods of approach, has served engineers and the public rather well during the last two decades. Neither approach guaranties catastrophic collapse prevention nor post‐earthquake realignment and repairs (PERR) due to major seismic events. As a result, most code‐compliant buildings can be regarded as relatively safe but practically disposable. The paper presents a new philosophy that leads to sustainable design of new structures and the upgrading of existing earthquake resisting moment frames. Repairability‐based design (RBD) relies on softening and control rather than strength and resistance to elevate seismic performance to economically viable, physical collapse prevention, damage control, and post‐earthquake realignment and repairs. The new approach was inspired by design led analysis (DLA), performance control (PC), and recent developments in rocking core‐moment frame design. DLA is a displacement based method of analysis with built‐in results. PC is the ability to design a structure in such a way as to expect predetermined modes of response at certain stages of loading, extents of damage, and drift ratios. This paper advocates higher performance objectives than current codes of practice do. Several demonstrative examples have been provided. 相似文献
45.
Zheng He Xiaoying Ou Jiangwei Li Jinping Ou 《Structure and Infrastructure Engineering》2019,15(8):1025-1035
Considering residual service life, this paper presents a collapse safety margin-oriented seismic retrofit strategy for corroded reinforced concrete (RC) frames using fibre reinforced plastics (FRP). With the assumed uniform corrosion model, corrosion-induced initial damage combined with subsequent earthquake-induced damage is identified by the multi-mode-based global damage model developed previously. The collapse-level earthquake intensity determined by incremental dynamic analyses (IDA) with the damage model and the maximum considered earthquake (MCE)-level intensity considering residual service life are combined to generate the time-variant collapse safety margin assessment of corroded RC structures. Based on this assessment, the collapse safety margin-oriented FRP seismic retrofit strategy is proposed and demonstrated on a 4-storey frame. The damage model originally developed for earthquake scenarios has also exhibited its rationality for characterising corrosion-induced initial damage and its influence on coupled damage development with subsequent earthquake excitation. Seismic retrofitting with FRP composites should consider the effects of the corrosion development stage, target collapse safety margin and residual service life. FRP retrofits can cause decreases in the MCE-level collapse probability and increases in the collapse resistance of corroded RC structures. Retrofitting carried out at different times achieves different efficiencies and different time-variant collapse safety margins within the residual service life. 相似文献
46.
随着科学技术的发展,微小零件广泛应用于各个领域,而微细铣削技术变得越来越重要。在微细铣削中,对刀具磨损的研究占有重要地位。采用直径1 mm的TiAlN涂层平头铣刀,针对微细铣削黄铜H59时的刀具侧刃磨损进行试验研究。发现随着铣削长度的增加,侧刃磨损量呈上升趋势。切削长度为200 m时,两组试验的磨损带宽度变化由快变慢,出现变化临界点。对刀具磨损形式与机制进行分析,发现刀具出现涂层脱落、刀尖钝圆半径变大和微崩刃现象,分析其发生机制为磨粒磨损与粘结磨损。以侧刃后刀面磨损带宽度为试验指标进行正交试验,研究铣削参数对刀具侧刃后刀面磨损的影响主次顺序及最优参数组合。结果表明:每齿进给量、轴向切深、主轴转速和径向切深对刀具磨损的影响依次减少;试验所得最优参数组合为f_z=2μm/齿,a_p=0.3 mm,n=60 000 r/min,a_e=0.15 mm。 相似文献
47.
48.
49.
套管水泥环组合抗挤强度模型及其弹性分析 总被引:6,自引:2,他引:6
建立了套管水泥环组合抗挤强度模型,导出了管外水泥环对套管屈服抗挤强度的影响系数,提出了套管水泥环组合抗挤强度弹性概念;计算分析了管外水泥环的存在对套管屈服抗挤强度的影响程度,并对套管水泥环组合抗挤强度对套管水泥环参数变化的敏感性,即套管水泥环组合抗挤强度弹性进行了计算分析。 相似文献
50.