全文获取类型
收费全文 | 4497篇 |
免费 | 101篇 |
国内免费 | 124篇 |
专业分类
电工技术 | 243篇 |
综合类 | 187篇 |
化学工业 | 862篇 |
金属工艺 | 314篇 |
机械仪表 | 440篇 |
建筑科学 | 427篇 |
矿业工程 | 190篇 |
能源动力 | 384篇 |
轻工业 | 258篇 |
水利工程 | 22篇 |
石油天然气 | 114篇 |
武器工业 | 13篇 |
无线电 | 76篇 |
一般工业技术 | 609篇 |
冶金工业 | 266篇 |
原子能技术 | 23篇 |
自动化技术 | 294篇 |
出版年
2024年 | 1篇 |
2023年 | 33篇 |
2022年 | 68篇 |
2021年 | 83篇 |
2020年 | 75篇 |
2019年 | 55篇 |
2018年 | 81篇 |
2017年 | 78篇 |
2016年 | 112篇 |
2015年 | 170篇 |
2014年 | 228篇 |
2013年 | 232篇 |
2012年 | 281篇 |
2011年 | 297篇 |
2010年 | 199篇 |
2009年 | 242篇 |
2008年 | 175篇 |
2007年 | 237篇 |
2006年 | 244篇 |
2005年 | 257篇 |
2004年 | 242篇 |
2003年 | 218篇 |
2002年 | 173篇 |
2001年 | 135篇 |
2000年 | 131篇 |
1999年 | 154篇 |
1998年 | 125篇 |
1997年 | 102篇 |
1996年 | 64篇 |
1995年 | 62篇 |
1994年 | 57篇 |
1993年 | 31篇 |
1992年 | 22篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有4722条查询结果,搜索用时 15 毫秒
1.
Material removal and surface damage of Ti3SiC2 ceramic during electrical discharge machining (EDM) were investigated. Melting and decomposition were found to be the main material removal mechanisms during the machining process. Material removal rate was enhanced acceleratively with increasing discharge current, ie, working voltage, ui, but increased deceleratively with pulse duration, te. Microcracks in the surface and loose grains in the subsurface resulted from thermal shock were confirmed, and the surface damage in Ti3SiC2 ceramic led to a degradation of both strength and reliability. 相似文献
2.
闩体的刚度和强度必须满足设计要求。用有限元法对复杂结构件进行力学性能分析是非常有效的方法。采用ANSYS软件对闩体进行了刚度和强度分析,得出了有用的结论,可供相关设计借鉴。 相似文献
3.
4.
5.
F. Vodák 《Cement and Concrete Research》2005,35(7):1447-1451
Concrete applied for construction of nuclear power plant (NPP) Temelín (Czech Republic) has been exposed to γ-irradiation up to dose 6×105 Gy. Depending on the level of irradiation, changes in strength, porous structure and phase composition of the concrete have been studied. It is found that irradiation lowers both the strength of concrete (about 10%) and volume (resp. surface) of porous space. On the other hand, γ-irradiation increases the ratio of calcite, CaCO3, in the concrete. Observed effects are discussed with respect to safety of NPPs. 相似文献
6.
7.
《Ergonomics》2012,55(7):484-500
The effects of a pressurized suit on human performance were investigated. The suit is known as an Extra-Vehicular Mobility Unit (EMU) and is worn by astronauts while working outside their spacecraft in a low earth orbit. Isolated isokinetic joint torques of three female and three male subjects (all experienced users of the suit in 1G gravity) were measured while working at 100% and 80% of their maximum voluntary torque (MVT, which is synonymous with maximum voluntary contraction (MVC)). It was found that the average decrease in the total amount of work (the sum of the work in each repetition until fatigue) done when the subjects were wearing the EMU were 48% and 41% while working at 100% and 80% MVT, respectively. There is a clear relationship between the MVT and the time and amount of work done until fatigue. Here, the time to fatigue is defined as the ending time of the repetition for which the computed work done during that repetition dropped below 50% of the work done during the first repetition. In general the stronger joints took longer to fatigue and did more work than the weaker joints. It was found that the EMU decreases the work output at the wrist and shoulder joints the most, due to the EMU joint geometry. The EMU also decreased the joint range of motion. The average total amount of work done by the test subjects increased by 5.2% (20.4%) for the unsuited (suited) case, when the test subjects decreased the level of effort from 100% to 80% MVT. Also, the average time to fatigue increased by 9.2% (25.6%) for the unsuited (suited) case, when the test subjects decreased the level of effort from 100% to 80% MVT. It was also found that the experimentally measured torque decay could be predicted by a logarithmic equation. The absolute average errors in the predictions were found to be 18.3% and 18.9% for the unsuited and suited subjects, respectively, when working at 100% MVT, and 22.5% and 18.8% for the unsuited and suited subjects, respectively, when working at 80% MVT. These results could be very useful in the design of future EMU suits and the planning of Extra-Vehicular Activity (EVA) for the future International Space Station assembly operations. 相似文献
8.
对汽包双室平衡容器水位温压补偿控制系统进行了探讨和研究,根据温压补偿模型,分析了P L C系统难以独立实现的原因以及查表法的缺陷,提出了P L C系统与上位机系统相结合的水位温压实时连续补偿的综合控制策略,提出并分析比较了三种体系结构及其实现原理和技术,工程应用结果表明该控制系统提高了水位控制的实时性、稳定性、准确性和安全性。 相似文献
9.
Corrosion-resistant analogue of Hadfield steel 总被引:2,自引:0,他引:2
V.G. Gavriljuk A.I. Tyshchenko O.N. Razumov Yu.N. Petrov B.D. Shanina H. Berns 《Materials Science and Engineering: A》2006,420(1-2):47-54
The concept of alloying austenitic steels with carbon + nitrogen is used for the development of a corrosion-resistant austenitic CrMn steel having an impact wear resistance close to that of the Hadfield steel. A higher stabilization of the austenitic phase by C + N, as compared to carbon or nitrogen alone, is substantiated by ab initio calculation of the electron structure, measurements of the concentration of free electrons and calculations of the phase equilibrium. Based on these results, the compositions (mass%) Cr18Mn18C0.34N0.61 and Cr18Mn18C0.49N0.58 were melted and tested along with Hadfield steel Mn12C1.2. Mechanical tests have shown that, as compared to the Hadfield steel, the experimental steels possess a higher strength, plasticity, hardness and the same resistance to impact wear. TEM studies of the surface layer after impact treatment revealed a mixture of the amorphous phase, nanocrystals and fine-twinned austenite. At the same time, using Mössbauer spectroscopy of conversion electrons, the ferromagnetic ordering was found in the surface layer of up to 10 μm in depth, which is the sign of the strain-induced martensitic phase. The hypothesis of a transition from the low-spin to the high-spin state of the iron atoms within the thin twins in austenite was proposed in order to interpret the discrepancy between TEM and Mössbauer studies. Potentiodynamic measurements and immersion tests show that the CrMnCN steels possess a significantly higher pitting potential and resistance to general corrosion in comparison with Hadfield steel. 相似文献
10.
介绍了微机控制系统在卧式内燃湿背式三回程小型锅炉控制中的应用。主要阐述微机控制系统的系统组成、控制方式和主要功能。 相似文献