全文获取类型
收费全文 | 8838篇 |
免费 | 417篇 |
国内免费 | 81篇 |
专业分类
电工技术 | 194篇 |
综合类 | 89篇 |
化学工业 | 1621篇 |
金属工艺 | 218篇 |
机械仪表 | 296篇 |
建筑科学 | 351篇 |
矿业工程 | 13篇 |
能源动力 | 279篇 |
轻工业 | 463篇 |
水利工程 | 38篇 |
石油天然气 | 44篇 |
武器工业 | 2篇 |
无线电 | 1759篇 |
一般工业技术 | 1594篇 |
冶金工业 | 1214篇 |
原子能技术 | 88篇 |
自动化技术 | 1073篇 |
出版年
2023年 | 94篇 |
2022年 | 136篇 |
2021年 | 192篇 |
2020年 | 147篇 |
2019年 | 131篇 |
2018年 | 193篇 |
2017年 | 192篇 |
2016年 | 192篇 |
2015年 | 195篇 |
2014年 | 289篇 |
2013年 | 536篇 |
2012年 | 445篇 |
2011年 | 484篇 |
2010年 | 385篇 |
2009年 | 446篇 |
2008年 | 450篇 |
2007年 | 409篇 |
2006年 | 374篇 |
2005年 | 319篇 |
2004年 | 301篇 |
2003年 | 304篇 |
2002年 | 255篇 |
2001年 | 230篇 |
2000年 | 212篇 |
1999年 | 197篇 |
1998年 | 469篇 |
1997年 | 314篇 |
1996年 | 218篇 |
1995年 | 144篇 |
1994年 | 125篇 |
1993年 | 146篇 |
1992年 | 82篇 |
1991年 | 79篇 |
1990年 | 70篇 |
1989年 | 50篇 |
1988年 | 53篇 |
1987年 | 54篇 |
1986年 | 59篇 |
1985年 | 32篇 |
1984年 | 32篇 |
1983年 | 20篇 |
1981年 | 40篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1978年 | 26篇 |
1977年 | 40篇 |
1976年 | 43篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1971年 | 12篇 |
排序方式: 共有9336条查询结果,搜索用时 15 毫秒
31.
A quartz microbalance technique has been used to study the growth of4He and H2 adsorbed on sodium. In contrast to cesium, adsorption of4He and H2 do occur on a sodium surface. 相似文献
32.
Charles A. Bateman Lijie Zhang Helen M. Chan Martin P. Harmer 《Journal of the American Ceramic Society》1992,75(5):1281-1283
It is experimentally observed that the peritectic reaction, 211 + liquid → 123, can be driven essentially to completion in 1 h at an undercooling of only ∽30°C. The kinetic data, together with the observed microstructures, are inconsistent with the normal mechanism of the peritectic reaction. It is proposed that the mechanism of the reaction involves dissolution of 211 particles into the liquid and precipitation of solid 123. The aligned grain structure is explained through sympathetic nucleation of new 123 grains on existing grains. 相似文献
33.
钢结构稳定设计——理论与实践 总被引:2,自引:0,他引:2
本文提出了实际工程结构的非线性理论设计和分析方法(NIDA),并以澳门回归纪念馆的设计为例,展示了本方法的优越性.在设计过程中,设计者无需假设K系数和有效长度,在结构分析完成后便可迅速完成设计,因此本文提出的方法既经济又便利.尽管对于钢框架在往复荷载及动力荷载作用下的弹塑性大位移分析已经非常成熟,但本文的方法开创了结构的非线性分析及设计的新纪元,能够对现行的设计方法理论起到巨大的推动作用. 相似文献
34.
Chan T.H. Yeung R.W. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(7):1992-1995
We establish a one-to-one correspondence between information inequalities and group inequalities. The major implication of our result is that we can prove information inequalities by proving the corresponding group inequalities, and vice versa. By giving a group-theoretic proof for all Shannon-type inequalities, we suggest that new inequalities could be discovered by making use of the rich set of tools in group theory. On the other hand, via a non-Shannon-type information inequality discovered by Zhang and Yeung (1997), we obtain a new inequality in group theory whose meaning is yet to be understood 相似文献
35.
A hybrid PC/PLC architecture for manufacturing-system control—theory and implementation 总被引:1,自引:0,他引:1
A. Ramirez-Serrano S. C. Zhu S. K. H. Chan S. S. W. Chan M. Ficocelli B. Benhabib 《Journal of Intelligent Manufacturing》2002,13(4):261-281
This paper presents a novel and generic PC/PLC-based software/hardware architecture for the control of flexible manufacturing workcells. The proposed implementation methodology is based on the utilization of any one of the available formal discrete-event-system control theories in conjunction with state-of-the-art industrial programmable-logic controllers (PLCs). The methodology has been illustrated to be a viable technique through its actual implementation in our laboratory using a robotic-workcell testbed. The specific control theory used is a combination of Extended Moore Automata and Ramadge-Wonham Automata that has been developed by our research group. The modular control software architecture has been developed for MS-Windows environments (running on one PC interfaced to the PLCs) and allows the use of different formal control theories as well as different commercial PLC hardware. The effective graphical user interface provides a transparent programming environment, where users are not expected to have a full knowledge of the formal control theory used. 相似文献
36.
37.
Effect of grain boundary phase on the thermal conductivity of aluminium nitride ceramics 总被引:2,自引:0,他引:2
Ching -Fong Chen M. E. Perisse A. F. Ramirez N. P. Padture H. M. Chan 《Journal of Materials Science》1994,29(6):1595-1600
AIN with high thermal conductivity was fabricated by pressureless sintering with Y2O3 as the sintering aid. The thermal conductivity was observed to increase with sintering time (up to 8 h) at 1810 °C. The distribution of the sintering aid was identified as one of the major factors influencing the thermal conductivity in AIN. Non-uniform distribution of the grain boundary phase was found to be associated with a significant amount of porosity, resulting in the enhancement of phonon scattering and thereby lowering the thermal conductivity. 相似文献
38.
Chan C.C. Zheng Ming Zhao Qian C. Meng S. 《Industrial Electronics, IEEE Transactions on》2002,49(6):1342-1344
Based on the concepts of cascade multilevel converters and one-cycle technique, comparisons are conducted to characterize the distortion of the pulsewidth modulation (PWM) and one-cycle control methods that were applied to converters. Simulation results for the different control schemes are obtained in PSIM software initially to see the effect of one-cycle control different from that of PWM control. Through the comparisons, the advantages and disadvantages are identified for each method. The one-cycle scheme is better than PWM control in reducing undesirable harmonics and tracing dynamic waveforms. Simulation and experimental results are also provided to verify the conclusions. 相似文献
39.
In this paper, filters with rectangular fibres arranged in a staggered and parallel array and placed transverse to the flow
are studied numerically. A two- dimensional flow field is obtained by solving Navier–Stokes equations with the control volume
method. Periodic boundary conditions are introduced in the calculation. In order to achieve higher accuracy, a second-order
upwind scheme is adopted and a fine mesh is arranged near the fibre and the symmetrical plane of the flow field where large
gradients in velocity are expected. Particle trajectories are calculated by solving the corresponding Lagrangian equation
of motion to obtain the collection efficiency of a single rectangular fibre, in which positions of the approaching particles
on the inlet plane of the flow field are randomly distributed according to the Monte-Carlo principle. The simulation considers
all the important mechanisms of particle capture including interception, inertial impaction and Brownian motion. Effects of
fibre aspect ratio, filter packing density, particulate size and Reynolds number on the collection efficiency are numerically
determined. The volumetric packing density ranges from 0.4 to 4% and the particle diameter is from 0.01 μm to 2 μm. Reynolds
number based on the height of computational domain varies from 20 to 100 and the aspect ratio is from 0.1 to 10. Simulations
with and without Brownian motion are carried out for different Reynolds numbers, packing densities and aspect ratios and the
results show that Brownian effects are significant for particles smaller than 1 μm.
Received 25 May 2001 相似文献
40.
PURPOSE: Although traditional ideal convergence (the sum of taper of the opposite sides) for crown preparation has been arbitrarily set at 4 degrees to 10 degrees, some believe absolute parallelism yields the highest retention. This study examined the relationship between the degree of convergence of a machined metal die and the retention of its casting. MATERIALS AND METHODS: The method used was that of cementing cast metal crowns onto full crown preparations on brass dies with varying convergence angles, and then recording the force required to remove the crowns from the dies in a vertical direction using a Tate-Emery Testing Machine and Load Indicator. RESULTS: It was found that retention (i.e., the force needed to remove the cemented castings from the die in their common long axis) increases from 0 degree convergence to peak between 6 degrees to 12 degrees convergence. It also seems that a critical film thickness does exist for optimum retention, and that film thicknesses smaller than the critical thickness may be responsible for the phenomenon that we have observed and directly related to the convergence angle itself. CONCLUSIONS: There seems to be experimental data supporting the use of traditionally taught convergence. Our study found that convergence angles between 6 degrees and 12 degrees seem to be optimum for tooth crown preparation when one plans to use zinc phosphate cement. Convergence angles of less than 6 degrees may not be desirable even if they can be clinically achieved. The results of our study indicate that a relationship exists between the convergence angle and the critical cement thickness that is necessary to realize the maximum strength properties of zinc phosphate cement. 相似文献