全文获取类型
收费全文 | 71483篇 |
免费 | 7598篇 |
国内免费 | 3171篇 |
专业分类
电工技术 | 11843篇 |
技术理论 | 2篇 |
综合类 | 6687篇 |
化学工业 | 2371篇 |
金属工艺 | 2596篇 |
机械仪表 | 10550篇 |
建筑科学 | 3037篇 |
矿业工程 | 1892篇 |
能源动力 | 1525篇 |
轻工业 | 1248篇 |
水利工程 | 1389篇 |
石油天然气 | 1294篇 |
武器工业 | 1325篇 |
无线电 | 13301篇 |
一般工业技术 | 7240篇 |
冶金工业 | 1999篇 |
原子能技术 | 1134篇 |
自动化技术 | 12819篇 |
出版年
2025年 | 405篇 |
2024年 | 1338篇 |
2023年 | 1407篇 |
2022年 | 1686篇 |
2021年 | 1906篇 |
2020年 | 2154篇 |
2019年 | 1722篇 |
2018年 | 1718篇 |
2017年 | 2387篇 |
2016年 | 2862篇 |
2015年 | 3116篇 |
2014年 | 4297篇 |
2013年 | 3866篇 |
2012年 | 5169篇 |
2011年 | 5252篇 |
2010年 | 3909篇 |
2009年 | 3995篇 |
2008年 | 4046篇 |
2007年 | 4917篇 |
2006年 | 4350篇 |
2005年 | 3479篇 |
2004年 | 2945篇 |
2003年 | 2638篇 |
2002年 | 2092篇 |
2001年 | 1812篇 |
2000年 | 1565篇 |
1999年 | 1272篇 |
1998年 | 988篇 |
1997年 | 1018篇 |
1996年 | 780篇 |
1995年 | 604篇 |
1994年 | 560篇 |
1993年 | 423篇 |
1992年 | 309篇 |
1991年 | 229篇 |
1990年 | 205篇 |
1989年 | 163篇 |
1988年 | 139篇 |
1987年 | 88篇 |
1986年 | 50篇 |
1985年 | 54篇 |
1984年 | 64篇 |
1983年 | 33篇 |
1982年 | 38篇 |
1981年 | 28篇 |
1980年 | 18篇 |
1977年 | 18篇 |
1959年 | 12篇 |
1956年 | 12篇 |
1955年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
A serious problem in motion control is the occurrence of torque ripple. Since a direct drive (DD) motor with a magnet rotor uses a rare-earth magnet, the torque ripple is more serious than that of conventional servomotors. This paper presents an auto-compensation of torque ripple using a software-implemented torque observer. The frequency and amplitude of torque ripple can be obtained in the controller by using the estimated torque from an observer, and the autonomous generation of a compensating current component for a torque ripple is possible. The proposed algorithm has been verified by experiments. 相似文献
2.
3.
Sanghoon Lee Chris Podilchuk Vidhya Krishnan Alan C. Bovik 《The Journal of VLSI Signal Processing》2003,34(1-2):149-166
By exploiting new human-machine interface techniques, such as visual eyetrackers, it should be possible to develop more efficient visual multimedia services associated with low bandwidth, dynamic channel adaptation and robust visual data transmission. In this paper, we introduce foveation-based error resilience and unequal error protection techniques over highly error-prone mobile networks. Each frame is spatially divided into foveated and background layers according to perceptual importance. Perceptual importance is determined either through an eye tracker or by manually selecting a region of interest. We attempt to improve reconstructed visual quality by maintaining the high visual source throughput of the foveated layer using foveation-based error resilience and error correction using a combination of turbo codes and ARQ (automatic reQuest). In order to alleviate the degradation of visual quality, a foveation based bitstream partitioning is developed. In an effort to increase the source throughput of the foveated layer, we develop unequal delay-constrained ARQ (automatic reQuest) and rate compatible punctured turbo codes where the punctual pattern of RCPC (rate compatible punctured convolutional) codes in H.223 Annex C is used. In the simulation, the visual quality is significantly increased in the area of interest using foveation-based error resilience and unequal error protection; (as much as 3 dB FPSNR (foveal peak signal to noise ratio) improvement) at 40% packet error rate. Over real-fading statistics measured in the downtown area of Austin, Texas, the visual quality is increased up to 1.5 dB in PSNR and 1.8 dB in FPSNR at a channel SNR of 5 dB. 相似文献
4.
This paper presents a highly stable steady-state torque control system with a feedback of a secondary current signal. The torque control system is constructed with a feedback of the secondary current (I2) signal using a quick response magnetic-field sensor constructed with an amorphous core multivibrator bridge, which can solve the secondary resistance change problem for temperature variation in the IM. Moreover, we added a state feedback to the system to improve the response speed for the unit step function of a torque order. The I2 sensor method has advantages especially at a low-speed range, in which conventional method using an integrator shows control errors. 相似文献
5.
Hugh S. Fairman 《Color research and application》1995,20(1):44-49
In 1993, the American Society for Testing and Materials carried out a field test of newly calculated tristimulus weighting factors. These weighting factors had been calculated by a method proposed by Venable. the test also included a method of correction for bandpass dependence put forth by Stearns. the purpose of the trial was to assess the possible reduction in bandpass dependence introduced by each of these sets of weights. A large number of sets of spectral data were gathered from the cooperators in the field test. Results of integration by the various sets of tristimulus weighting factors were calculated. A total of 15 120 color differences were calculated and statistics were derived to test the probable error resulting from each method of correction. Errors attributable to bandpass dependence were on the order of a few tenths to as much as one CIELAB unit when uncorrected weight sets were used. These errors could be reduced to a few hundreths of a CIELAB unit, and in some cases to a few thousandths of a unit, by employing one correcting strategy or the other. an overall mix of strategies was ultimately chosen to minimize the bandpass dependence over the entire range of weight sets. Utilizing this mixed strategy, the median error introduced into 10-nm integration by bandpass dependence was only 0.004 CIELAB units. © 1995 John Wiley & Sons, Inc. 相似文献
6.
7.
W. Claeys V. Quintard S. Dilhaire D. Lewis Y. Danto 《Quality and Reliability Engineering International》1994,10(4):289-295
We have recently developed an optical contactless method for testing the quality of solder joints during accelerated thermal cycling ageing processes.1 The method was based upon the measurement of the dynamic thermal behaviour of the joint to short bursts of Joule heating. It has proved to be efficient in revealing the formation of cracks at the lead-solder interface. We present a method to evaluate ageing at a much earlier stage in the cycling process. We have observed in earlier work,1 that before cracks appear, structural changes occur in the solder at the lead-solder interface. The thermal response of the solder joint is recorded over time to a Peltier heat perturbation produced by flowing a current pulse through the interface where structural changes occur. The key point in this method is to discriminate the Peltier effect from the Joule thermal response because both effects generate heat. The variation of the early Peltier response in the thermal cycling ageing tests is seen as a quantitative signature of the structural changes in the lead-solder interface. 相似文献
8.
A new principle and arrangement for directly determining the angle of incidence of an optical beam on an object are proposed and demonstrated. The novelty of the approach lies in the realization of a ‘smart object’, which extracts a portion of the incident beam's power into an optical waveguide attached to the object's surface or embedded in its body for converting the angle of incidence into the position of a guided beam with finite lateral extent. This ‘integrated optical light pointer’ beam is accomplished by means of creating additional degrees of freedom on the target in two different ways. While a first type is based on introducing spatial variations of the waveguide thickness, a second type makes use of a chirp of the grating periodicity. The feasibility for practical applications has been experimentally demonstrated by a direct comparison with a commercial high-resolution encoder, resulting in an r.m.s. error of <30′'. Measurements have been performed for chips fabricated based on replicated polycarbonate substrates and with no external optics, showing the great potential of this approach for realizing low-cost yet high-performance miniature goniometers. 相似文献
9.
Takashi Ishikawa Sunao Sugimoto Masamichi Matsushima Yoichi Hayashi 《Composites Science and Technology》1995,55(4):349-363
Compression-after-impact (CAI) tests have been conducted for quasi-isotropic thick plates with 48 plies by using the NASA method and on plates with 32 plies by using the SACMA method. Specimens are made of CF/PEEK (APC-2) and conventional CF/epoxy for the NASA plates and CF/epoxy for the SACMA plates. In the NASA CAI tests, the sequence of delamination buckling and its propagation is clearly revealed through various experimental techniques. One major technique is moiré topography, and the other is thermo-mechanical stress analysis with a high-accuracy infrared sensor. The arrest of delamination propagation just before catastrophic failure due to high fracture toughness is clearly captured by the moiré camera. This behavior provides good CAI values of CF/PEEK. The initial buckling properties of the delaminated region by the impact are then extensively discussed. Numerical predictions of initial buckling stress have been obtained by modelled geometry of the delaminated region simplified from its precise structure clarified by ultrasonic C-scanning. They agree fairly well with the experimental results. The in-plane stress distribution in the delaminated region before initial buckling is measured by an infrared stress graphic system. This compared favorably with finite element predictions. Two types of symmetric buckling modes with respect to the central plate surface, twin and single peak ones, are experimentally captured. 相似文献
10.
Solving regularized least squares with qualitatively controlled adaptive cross‐approximated matrices
The adaptive cross‐approximation (ACA) technique is applied to accelerating an inverse‐problem solver that estimates charge distribution on a dielectric spacer. The ACA generates an approximated system‐matrix that enables us to carry out high‐speed inverse calculation. We designed an approximation procedure based on ACA with some additional concepts, that is, (a) partitioning of matrix based on algebraic information, (b) approximation quality control based on matrix norms, and so on. The tested solver (LSQR for regularized least squares) with ACA demonstrates about 10 times faster performance than that without ACA. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(3): 10–18, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20326 相似文献