全文获取类型
收费全文 | 7002篇 |
免费 | 460篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 68篇 |
综合类 | 1篇 |
化学工业 | 1810篇 |
金属工艺 | 179篇 |
机械仪表 | 173篇 |
建筑科学 | 274篇 |
矿业工程 | 25篇 |
能源动力 | 266篇 |
轻工业 | 950篇 |
水利工程 | 47篇 |
石油天然气 | 42篇 |
无线电 | 502篇 |
一般工业技术 | 1516篇 |
冶金工业 | 314篇 |
原子能技术 | 56篇 |
自动化技术 | 1244篇 |
出版年
2024年 | 31篇 |
2023年 | 71篇 |
2022年 | 119篇 |
2021年 | 219篇 |
2020年 | 208篇 |
2019年 | 183篇 |
2018年 | 303篇 |
2017年 | 330篇 |
2016年 | 382篇 |
2015年 | 230篇 |
2014年 | 330篇 |
2013年 | 676篇 |
2012年 | 386篇 |
2011年 | 519篇 |
2010年 | 388篇 |
2009年 | 410篇 |
2008年 | 367篇 |
2007年 | 333篇 |
2006年 | 268篇 |
2005年 | 195篇 |
2004年 | 179篇 |
2003年 | 156篇 |
2002年 | 150篇 |
2001年 | 83篇 |
2000年 | 88篇 |
1999年 | 77篇 |
1998年 | 94篇 |
1997年 | 82篇 |
1996年 | 71篇 |
1995年 | 50篇 |
1994年 | 51篇 |
1993年 | 40篇 |
1992年 | 36篇 |
1991年 | 32篇 |
1990年 | 20篇 |
1989年 | 22篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 29篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 12篇 |
1979年 | 15篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1974年 | 11篇 |
排序方式: 共有7467条查询结果,搜索用时 15 毫秒
991.
A smart shear connection system was tested in order to be used in manufactured elements of a lattice of wooden slats and a cross offset. This type of floor element can present advantages both in terms of weight and suitable insulating filler (Adalberth et al. 2001; Kawasaki and Kawai 2006; Kermani and Hairstans 2006; Dodoo et al. 2014). This connection is made to provide a substitute for a glue connection. The shear connection proposed is made by double-sided grooving timber interfaces to form a cross section. A specifically designed test assembly was constructed to measure and guarantee homogeneous contact pressure in interface test specimens. Shear test results are presented and compared in terms of capacity and stiffness with glue connections. The principal conclusions are as follows: the allowable shearing resistance of the grooved timber–timber joints can approximately reach the resistance of glued connections. The stiffness of the joints is improved by increasing the pre-stress applied for holding contact in the assembly. The grooved timber-to-timber joints exhibit non-linear behaviour which dominates the behaviour of the whole system. Therefore, the behaviour of a unit connection must be determined to obtain the mean load-carrying capacity and stiffness of a system with grooved connections. 相似文献
992.
本文通过对里维特的《北桥》和侯麦的《飞行员的妻子》进行比较.讨论了电影中的“创造性空间”和“空间连续性”的概念,以及它们在描述巴黎的“可读性”时的不同效果。侯麦使用了城市中的日常标志物以在影片中重建真实城市的空间地理,并引导观众们的方向认知。而里维特则选择了一些对于游客来说更加有名的标志性建筑.作为“巴黎之海”的观察点。侯麦的城市策略是对日常性的精确刻画,而里维特的角色们则在超现实的心理地图中进行“都市漫游”,并凸现出“消失中的巴黎”。但是由于里维特遵守由叙事所限定的时间连贯性,影片叙事空间中的“高度统一场”得到了尊重,在观众的知觉中影片的情节依然是连续可读的。 相似文献
993.
Space and competition 总被引:1,自引:0,他引:1
We review the argument that incorporating space in economic models has two important consequences: first, the hypothesis of perfect competition becomes untenable, and second, the distinction between private and public goods becomes blurred. We summarize recent work pointing to alternative incentive systems that might lead to efficient location decisions and pricing policies. 相似文献
994.
Mo Wu Y. I. Alivov Hadis Morkoç 《Journal of Materials Science: Materials in Electronics》2008,19(10):915-951
With scaling of the gate length downward to increase speed and density, the gate dielectric thickness must also be reduced.
However, this practice which has been in effect for many decades has reached a fundamental limitation because gate dielectric
thicknesses in the range of tunneling have been reached with the SiO2 dielectric layer for MOSFETs. Consequently, the gate dielectrics with higher dielectric constants, dubbed the “high-κ”, which
allow scaling with much larger thicknesses have become active research and development topics. In this review technological
issues associated with the likely high-κ materials which are under consideration as well as challenges, and solution to them,
they bring about in the fabrication of Si MOSFET are discussed. Moreover, in order to squeeze more speed out of CMOS, channels
for both n- and p-type MOSFET enhanced with appropriate strain and the concepts behind them are discussed succinctly. Finally, the longer term
approach of replacing Si with other channel materials such as GaAs (InGaAs) for n-channel and Ge for p-channel along with technological developments of their preparation on Si and likely gate oxide developments are treated in
some detail. 相似文献
995.
Chaste J Lechner L Morfin P Fève G Kontos T Berroir JM Glattli DC Happy H Hakonen P Plaçais B 《Nano letters》2008,8(2):525-528
We report on microwave operation of top-gated single carbon nanotube transistors. From transmission measurements in the 0.1-1.6 GHz range, we deduce device transconductance gm and gate-nanotube capacitance Cg of micro- and nanometric devices. A large and frequency-independent gm approximately 20 microS is observed on short devices, which meets the best dc results. The capacitance per unit gate length of 60 aF/microm is typical of top gates on a conventional oxide with epsilon approximately 10. This value is a factor of 3-5 below the nanotube quantum capacitance which, according to recent simulations, favors high transit frequencies fT=gm/2piCg. For our smallest devices, we find a large fT approximately 50 GHz with no evidence of saturation in length dependence. 相似文献
996.
Proust-Lima Cécile; Amieva Hélène; Letenneur Luc; Orgogozo Jean-Marc; Jacqmin-Gadda Hélène; Dartigues Jean-Fran?ois 《Canadian Metallurgical Quarterly》2008,23(3):608
In cognitive aging research, the study of a general cognitive factor has been shown to have a substantial explanatory power over the study of isolated tests. The authors aimed at differentiating the impact of gender and education on global cognitive change with age from their differential impact on 4 psychometric tests using a new latent process approach, which intermediates between a single-factor longitudinal model for sum scores and an item-response theory approach for longitudinal data. The analysis was conducted on a sample of 2,228 subjects from PAQUID, a population-based cohort of older adults followed for 13 years with repeated measures of cognition. Adjusted for vascular factors, the analysis confirmed that women performed better in tests involving verbal components, while men performed better in tests involving visuospatial skills. In addition, the model suggested that women had a slightly steeper global cognitive decline with oldest age than men, even after excluding incident dementia or death. Subjects with higher education exhibited a better mean score for the 4 tests, but this difference tended to attenuate with age for tests involving a speed component. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
997.
998.
999.
Several papers on induced current electrical impedance tomography (IC-EIT) have dwelt on potential advantages of this technique over conventional EIT which uses applied current (AC-EIT). Experimental evidence that IC-EIT could surpass AC-EIT in similar imaging conditions is lacking. In this paper, we describe a system that can switch rapidly between both AC-EIT and IC-EIT. The system makes it possible to image objects in a saline-filled tank, providing data acquired in identical test conditions for comparing the performance of the two modes. The system uses eight circular coils and 16 electrodes to acquire 120 linearly independent measurements in IC-EIT and 104 in AC-EIT. Difference images were reconstructed from data acquired with both modes using the maximum a posteriori method. Spatial resolution was lower in IC-EIT images than in AC-EIT, especially in the radial direction. IC-EIT also exhibits a bias toward the center for positioning a conductivity perturbation. These results were obtained for a typical coil configuration widely used in the literature and may not be representative of alternate coil configurations. The system described in this paper provides stable experimental conditions for comparing the performance of the two EIT imaging modes and would be a valuable tool for validating new coil configurations. 相似文献
1000.
Selçuk Baktır Sandeep Kumar Christof Paar Berk Sunar 《Mobile Networks and Applications》2007,12(4):259-270
We propose a novel area/time efficient elliptic curve cryptography (ECC) processor architecture which performs all finite
field arithmetic operations in the discrete Fourier domain. The proposed architecture utilizes a class of optimal extension fields (OEF)
GF(q
m
) where the field characteristic is a Mersenne prime q = 2
n
− 1 and m = n. The main advantage of our architecture is that it achieves extension field modular multiplication in the discrete Fourier domain with only a linear number of base field GF(q) multiplications in addition to a quadratic number of simpler operations such as addition and bitwise rotation. We achieve
an area between 25k and 50k equivalent gates for the implementations over OEFs of size 169, 289 and 361 bits. With its low
area and high speed, the proposed architecture is well suited for ECC in small device environments such as sensor networks.
The work at hand presents the first hardware implementation of a frequency domain multiplier suitable for ECC and the first
hardware implementation of ECC in the frequency domain.
相似文献
Berk SunarEmail: |