全文获取类型
收费全文 | 6601篇 |
免费 | 1025篇 |
国内免费 | 576篇 |
专业分类
电工技术 | 1677篇 |
综合类 | 915篇 |
化学工业 | 243篇 |
金属工艺 | 297篇 |
机械仪表 | 446篇 |
建筑科学 | 1011篇 |
矿业工程 | 165篇 |
能源动力 | 290篇 |
轻工业 | 258篇 |
水利工程 | 256篇 |
石油天然气 | 224篇 |
武器工业 | 100篇 |
无线电 | 862篇 |
一般工业技术 | 682篇 |
冶金工业 | 137篇 |
原子能技术 | 170篇 |
自动化技术 | 469篇 |
出版年
2024年 | 37篇 |
2023年 | 100篇 |
2022年 | 179篇 |
2021年 | 228篇 |
2020年 | 225篇 |
2019年 | 204篇 |
2018年 | 200篇 |
2017年 | 304篇 |
2016年 | 366篇 |
2015年 | 357篇 |
2014年 | 384篇 |
2013年 | 406篇 |
2012年 | 568篇 |
2011年 | 576篇 |
2010年 | 400篇 |
2009年 | 392篇 |
2008年 | 397篇 |
2007年 | 430篇 |
2006年 | 414篇 |
2005年 | 351篇 |
2004年 | 279篇 |
2003年 | 243篇 |
2002年 | 193篇 |
2001年 | 154篇 |
2000年 | 130篇 |
1999年 | 133篇 |
1998年 | 85篇 |
1997年 | 71篇 |
1996年 | 79篇 |
1995年 | 58篇 |
1994年 | 60篇 |
1993年 | 35篇 |
1992年 | 44篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1980年 | 1篇 |
1979年 | 6篇 |
1959年 | 1篇 |
排序方式: 共有8202条查询结果,搜索用时 7 毫秒
1.
Mohammadmahdi Davoudi 《工程优选》2019,51(5):775-795
Although topology optimization is established for linear static problems, more effort is required for solving nonlinear plastic problems. A new topology optimization approach with equivalent static loads (ESLs) is suggested to find the optimum topologies and locations of plastic hinges of thin-walled crash boxes by considering crash-induced deformation, the main crash energy-absorbing mechanism. Together with finite element method crashworthiness analyses, considering all nonlinearities with rate-dependent plasticity, the method was developed using an appropriate time-incremental scheme of ESLs without removing any high values of loads. Analyses show that the crash boxes with optimum topologies have energy-absorbing capabilities equivalent to the original structure. The proposed method is evaluated for two crashes: a crash box at low speed and a double cell subjected to high-speed collision. The results indicate that this method captures nonlinear crushing behaviours and accurate locations of plastic hinges where, if proper reinforcements are made, energy absorption can be enhanced. 相似文献
2.
Longbang Qing Yuehua Cheng Ru Mu 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(11):2533-2543
Based on theoretical analysis and numerical simulation, the impact of steel fibres on the stress intensity factor (SIF) at the crack tip for cementitious composite was studied. The enhanced toughness of steel fibre reinforced cementitious composite (SFRC) in resisting cracks was explained by the decrement of SIF caused by steel fibre inclusions at the crack tip of the composite. The equivalent initial fracture toughness was used to characterize the crack initiation of SFRC. A simplified method for determining the of SFRC was proposed based on a linear regression method. Fracture tests were conducted on three‐point bending notched beams with different steel fibre volume fractions and specimen sizes to study the crack initiation behaviour of aligned steel fibre reinforced cementitious composite (ASFRC). of ASFRC was calculated, and the size effect of was analysed. The results showed that slightly increased with the steel fibre volume fraction and gradually became stable. For the tested specimens, whose heights varied between 40 and 100 mm, the specimen size had little impact on the . 相似文献
3.
4.
交通平衡分配下的公路桥收费策略 总被引:3,自引:0,他引:3
假定一个城市被一条河流分为两部分(如我国的武汉,重庆等市),河上至少架设了两座公路桥梁,本文研究在交通平衡状态下,怎样制定车辆过桥梁的收费水平,使获得的总收入最大,乘客的总行驶时间最少,对多车种问题,研究了等价的数学模型和算法。还对一个含两座桥梁与三种车型的简单算例,进行了计算与分析。 相似文献
5.
6.
碾压混凝土穿透型诱导缝不同扩展阶段的强度指标试验研究 总被引:2,自引:0,他引:2
在不同削弱度碾压混凝土轴拉试件的穿透型诱导缝周围粘贴了应变片,得到在不同应力状态下诱导缝应变发展规律为:在加载初期,离缝端不同距离的应变发展较为均匀,数值上相差不突出;随着荷载的增加,应变开始出现不均匀发展,离缝端越远,应变变化越缓慢;当接近最大荷载的阶段,缝端应变急速发展,试件瞬间断裂。应变从均匀发展变为不均匀发展,实质上隐含了诱导缝起裂、稳定发展、失稳断裂的整个过程,针对这一试验现象,结合断裂力学理论,建立了诱导缝不同开裂阶段的远场温度应力强度指标模型。 相似文献
7.
We obtain a necessary and sufficient condition for a discrete-time nonlinear system to be locally state equivalent to the nonlinear observer form. The result looks similar to the continuous counterpart except for the fact that Ad-operation is utilized instead of ad-operation. 相似文献
8.
The stress intensity factors for a short crack partially penetrating an inclusion of arbitrary shape
Some approximate solutions for predicting the stress intensity factor of a short crack penetrating an inclusion of arbitrary
shape have been developed under mode I and mode II loading conditions. The derivation of the fundamental formula is based
on the transformation toughening theory. The transformation strains in the inclusion are induced by the crack-tip field and
remotely applied stresses, and approximately evaluated by the Eshelby equivalent inclusion theory. As validated by detailed
finite element (FE) analyses, the developed solutions have good accuracy for different inclusion shape and for a wide range
of modulus ratio between inclusion and matrix material. 相似文献
9.
This research investigates the utility of passive microwave remote sensing instruments to accurately determine snow water equivalent (SWE) over large spatial extents. Three existing Special Sensor Microwave Imager (SSM/I) snow water equivalent algorithms produced by Chang, Tait and Goodison were evaluated for their ability to determine snow water equivalent in a snowpack containing substantial depth hoar, large faceted snow crystals. The Kuparuk River Watershed (8140 km2) test site on the North Slope of Alaska was chosen for its snowpack containing a think depth hoar layer and long history of ground truth data. A new regional snow water equivalent algorithm was developed to determine if it could produce better results than the existing algorithms in an area known to contain significant depth hoar. The four algorithms were tested to see how well they could determine snow water equivalent: (1) on a per pixel basis, (2) across swath-averaged spatial bands of approximately 850 km2, and (3) on a watershed scale. The algorithms were evaluated to see if they captured the annual spatial distribution in snow water equivalent over the watershed. Results show that the algorithms developed by Chang and from this research are generally within 3 cm of the spatially averaged snow water equivalents over the entire watershed. The algorithms produced by Chang, Tait, and in this research were able to predict the basin-wide ground measured snow water equivalent value within a percent error range from −32.4% to 24.4% in the years with a typical snowpack. None of the algorithms produce accurate results on a pixel-by-pixel scale, with errors ranging from −26% to 308%. 相似文献
10.