全文获取类型
收费全文 | 1803篇 |
免费 | 107篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 437篇 |
金属工艺 | 37篇 |
机械仪表 | 30篇 |
建筑科学 | 66篇 |
矿业工程 | 4篇 |
能源动力 | 55篇 |
轻工业 | 148篇 |
水利工程 | 7篇 |
石油天然气 | 3篇 |
无线电 | 211篇 |
一般工业技术 | 361篇 |
冶金工业 | 111篇 |
原子能技术 | 24篇 |
自动化技术 | 405篇 |
出版年
2023年 | 22篇 |
2022年 | 39篇 |
2021年 | 37篇 |
2020年 | 50篇 |
2019年 | 54篇 |
2018年 | 56篇 |
2017年 | 65篇 |
2016年 | 67篇 |
2015年 | 55篇 |
2014年 | 64篇 |
2013年 | 130篇 |
2012年 | 113篇 |
2011年 | 155篇 |
2010年 | 102篇 |
2009年 | 99篇 |
2008年 | 112篇 |
2007年 | 88篇 |
2006年 | 88篇 |
2005年 | 72篇 |
2004年 | 58篇 |
2003年 | 47篇 |
2002年 | 40篇 |
2001年 | 18篇 |
2000年 | 16篇 |
1999年 | 25篇 |
1998年 | 26篇 |
1997年 | 37篇 |
1996年 | 27篇 |
1995年 | 19篇 |
1994年 | 19篇 |
1993年 | 21篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1967年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1911条查询结果,搜索用时 0 毫秒
1.
2.
We study experimentally and theoretically two polarization effects in a vertical cavity surface emitting laser submitted to optical feedback. In a first experiment, we obtain flips between two linearly polarized laser modes up to a frequency of 50 MHz using an external cavity with a polarizer. In a second experiment, polarization self modulation is demonstrated up to a frequency of 2.6 GHz, using a quarter wave plate instead. Numerical calculations, based on a four levels model for the active medium, show a good agreement with the experiments. 相似文献
3.
A new method is presented to analyze reflection losses of integrated mirrors, taking into account the exact guided mode profile and assuming that this profile remains unchanged up to the reflecting plane. The fraction of the reflected light coupled to one of the guided modes of the output waveguide is calculated, taking into account the mirror reflection coefficient. The influence of both translation and tilt of the reflecting plane is investigated. The method applies for every guided mode and any reflection angles. Numerical calculations are derived for a 90° optical corner mirror 相似文献
4.
5.
6.
7.
S Sidney B Sternfeld SS Gidding DR Jacobs DE Bild A Oberman WL Haskell RS Crow JM Gardin 《Canadian Metallurgical Quarterly》1993,25(8):911-916
Symptom-limited, graded exercise treadmill testing was performed by 4,968 white and black adults, ages 18-30 yr, during the baseline examination for the Coronary Artery Risk Development in Young Adults (CARDIA) study. Compared with nonsmokers, the mean exercise test duration of smokers was 29-64 s shorter depending on race/gender group (all P < 0.001), but mean duration to heart rate 130 (beats.min-1) ranged from 20-50 s longer (P < 0.05). In each race/gender group, test duration to heart rates up to 150 was 15-35 s longer (P < 0.05) in smokers than in nonsmokers after adjustment for age, sum of skinfolds, hemoglobin, and physical activity score. The mean maximum heart rate was lower in smokers than in nonsmokers (difference ranging from 6.7 beats.min-1 in white men to 11.2 beats.min-1 lower in black women, P < 0.001), although maximum rating of perceived exertion was nearly identical in smokers and nonsmokers. Chronic smoking appears to blunt the heart rate response to exercise, so that exercise duration to submaximal heart rates is increased even though maximal performance is impaired. This may result from downloading of beta-receptors caused by smoking. Smoking status should be considered in the evaluation of physical fitness data utilizing submaximal test protocols, or else the fitness of smokers relative to nonsmokers is likely to be overestimated. 相似文献
8.
Delseny C. Pascal F. Jarrix S. Lecoy G. Dangla J. Dubon-Chevallier C. 《Electron Devices, IEEE Transactions on》1994,41(11):2000-2005
Noise measurements both on transmission line model (TLM) test structures and on associated HBT's are presented. Contact noise is proved to be negligible in the TLM's related to the base structure of transistors. A Hooge parameter for p++ doped GaAs is extracted. Activation energies are calculated from results versus temperature. Considering the TLM related to the structure of the emitter, it is shown that the g-r levels observed originate from the AlGaAs layer. Noise measurements on HBT's also exhibit excess noise. A value of the cutoff frequency between the equivalent input current white noise and the 1/f component is given. The base current dependencies associated with different measurement configurations suggest the 1/f noise to come from the base or the emitter-base junction. The g-r components are studied as a function of temperature. Activation energies are deduced. Finally a comparison of the TLM and HBT noise results is presented. The presence of the complex DX center and of g-r levels in the base region are proposed as possible origins for the g-r noise in HBT's 相似文献
9.
Dielectric relaxation measurements are reported over a frequency range from 10−1 to 109 Hz as a function of exposure time for an epoxy resin-carbon fibre composite, ageing at 60 °C in water. Investigation of the nature of the dipole relaxation of the water molecules, indicates the nature of their interaction with the polymer matrix. Analysis of the dielectric relaxation spectra allow identification of processes that can be attributed to ‘free’ and ‘bonded’ water, water in micro-cracking, located in carbon fibre disbonds and plasticizing the polymer matrix. Identification of the various types of location in which water exists was aided by use of the Ng factor from the Kirkwood-Frölich equation, which describes the constraints on free dipole ration nature imposed by the environment in which it is located. These data indicate the power of the dielectric technique for quantitative analysis of water ingress into epoxy composites. 相似文献
10.
This paper presents a new massively parallel MIMD architecture, halfway between the Connection Machine and hypercubes based on 32-bit processors. It is built from specific 8-bit processors arranged in a 2-D grid and communicating by message transfers. We discuss the communication problems, the instruction set of the basic processing unit, the programmation of the whole array and the use of a high level data-flow language. 相似文献