全文获取类型
收费全文 | 36658篇 |
免费 | 4330篇 |
国内免费 | 2044篇 |
专业分类
电工技术 | 3471篇 |
综合类 | 3933篇 |
化学工业 | 3648篇 |
金属工艺 | 1602篇 |
机械仪表 | 5895篇 |
建筑科学 | 3385篇 |
矿业工程 | 1626篇 |
能源动力 | 1500篇 |
轻工业 | 502篇 |
水利工程 | 1185篇 |
石油天然气 | 1182篇 |
武器工业 | 614篇 |
无线电 | 2967篇 |
一般工业技术 | 7886篇 |
冶金工业 | 857篇 |
原子能技术 | 315篇 |
自动化技术 | 2464篇 |
出版年
2024年 | 261篇 |
2023年 | 614篇 |
2022年 | 1205篇 |
2021年 | 1233篇 |
2020年 | 1409篇 |
2019年 | 1039篇 |
2018年 | 1069篇 |
2017年 | 1355篇 |
2016年 | 1442篇 |
2015年 | 1543篇 |
2014年 | 2187篇 |
2013年 | 2032篇 |
2012年 | 2885篇 |
2011年 | 2925篇 |
2010年 | 2097篇 |
2009年 | 2081篇 |
2008年 | 1840篇 |
2007年 | 2438篇 |
2006年 | 2164篇 |
2005年 | 1767篇 |
2004年 | 1462篇 |
2003年 | 1333篇 |
2002年 | 1045篇 |
2001年 | 966篇 |
2000年 | 847篇 |
1999年 | 708篇 |
1998年 | 551篇 |
1997年 | 489篇 |
1996年 | 403篇 |
1995年 | 347篇 |
1994年 | 305篇 |
1993年 | 202篇 |
1992年 | 183篇 |
1991年 | 149篇 |
1990年 | 111篇 |
1989年 | 122篇 |
1988年 | 87篇 |
1987年 | 40篇 |
1986年 | 14篇 |
1985年 | 8篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1965年 | 3篇 |
1959年 | 5篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A. Palmeri F. Ricciardelli G. Muscolino A. De Luca 《Canadian Metallurgical Quarterly》2004,130(9):1052-1061
The equation of motion of linear dynamic systems with viscoelastic memory is usually expressed in a integrodifferential form, and its numerical solution is computationally heavy. In two recent papers, the writers suggested that the system memory be accounted for through the introduction of a number of additional internal variables. Following this approach, the motion of the system is governed by a set of first-order, linear differential equations, whose solution is quite easy. In this paper, the approach is extended to single-degree-of-freedom systems subjected to random, nonstationary excitation. The equations governing the time variation of the second-order statistics are derived, and an effective step-by-step solution procedure is proposed. Numerical example shows the accuracy of the procedure for white and nonwhite excitations. 相似文献
62.
本文提出基于切削振动相关性识别刀具磨损状态的研究思想,建立了车削中刀杆双向横振动系统及其单输入双输出系统的数学模型。理论和实验均表明,刀杆双向横振动之加速度响应在固有基频处的相干函数与刀具磨损状态之间有很好的规律性,它反映了两者之间的本质机理,并提供了识别刀具磨损状态的新途径。 相似文献
63.
变速切削系统振动频率的变化特征 总被引:1,自引:0,他引:1
本文主要讨论变速切削系统中颤振频率随机床主轴转速变化的规律。理论分析和试验结果都证明在变速切削中颤振频率随转速呈分段线性锯齿状变化。试验在立式铣床和普通车床上进行。 相似文献
64.
该文介绍一种简单、可靠、小巧的转速传感器。它的特点是在强振环境下仍具有很高的可靠,可用于坦克底盘、重型工程机械,燃气轮机组等机械作为转速监测。 相似文献
65.
A separation distance between adjacent buildings is provided to reduce the risk of pounding of adjacent buildings under seismic excitations. It should be recognized that the evaluation of the critical separation distance is a one-sided barrier crossing problem while the problem of structural design under seismic excitations is a two-sided crossing problem. A procedure for assessing the required separation distance with or without considering possible uncertainty in structural properties was presented based on the reliability methods and random vibration theory. The procedure was used to carry out parametric analyses. It is shown that use of the complete quadratic combination (CQC) rule with the modal responses employed for designing structures may over- or underestimate the critical separation distance, depending on the damping ratios and the closeness of the natural vibration periods of adjacent buildings. This is due to not only one-sided versus two-sided crossing problem but also the approximation in the CQC rule. Further, the effect of the uncertainty in structural properties on the estimated separation is investigated. The results indicate that this uncertainty tends to increase the required critical separation distance. 相似文献
66.
67.
Influence of electroosmotic treatment on the hydro-mechanical behaviour of clayey silts: preliminary experimental results 总被引:1,自引:0,他引:1
Laura Gabrieli Cristina Jommi Guido Musso Enrique Romero 《Journal of Applied Electrochemistry》2008,38(7):1043-1051
Preliminary results of an investigation focused on the influence of electrokinetic treatment on the mechanical and hydraulic
behaviour of clayey soils are presented. The experimental programme aims at providing a contribution to the sustainability
of contaminant extraction or containment via electroosmosis. Changes in the hydraulic and mechanical properties of two illitic
clayey soils, subjected to a DC electric field, were investigated. Samples of the two soils were subjected to electrokinetic
filtration, for different periods of time, and under different constant loads. Afterwards, they were tested under one-dimensional
compression to detect changes in stiffness and hydraulic conductivity due to the electrical treatment. After the application
of a DC field for a few hours, a small reversible increment in the average soil stiffness was observed, with respect to the
untreated soil, while the hydraulic conductivity was not affected substantially. Dramatic changes of the mechanical and hydraulic
soil properties, correlated to changes of the soil pH, were observed following non-conditioned electrokinetic treatment with
duration of the order of days. 相似文献
68.
69.
High molecular weight, high functionality diamino telechelic polybutadienes (TPBs) were synthesized by ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene (COD) in the presence of a chain transfer agent, 1,8-dicyano-4-octene, followed by lithium aluminum hydride reduction. Melt coupling of diamino TPB with anhydride-terminated polystyrene (PS-anh) resulted in the formation of styrene-butadiene-styrene (SBS) triblock copolymers; ca. 80% maximum conversion of PS-anh was achieved within 30 s. The results from SAXS, TEM, and rheological measurements of the coupling products confirmed the formation of SBS triblock copolymers having lamellar morphology. A fluorescent-labeled PS-anh was used to study the coupling kinetics by diluting the reactants by the addition of non-functional PS. 相似文献
70.
初轧机主传动系统扭转自激振动的稳定性 总被引:1,自引:0,他引:1
用变量摄动法对初轧机主传动系统扭转自激振动的稳定性进行了初步研究,讨论了稳定性条件,为初轧机打滑状态的诊断、监测提供了参考依据。 相似文献