全文获取类型
收费全文 | 2179篇 |
免费 | 118篇 |
国内免费 | 15篇 |
专业分类
电工技术 | 37篇 |
综合类 | 3篇 |
化学工业 | 467篇 |
金属工艺 | 81篇 |
机械仪表 | 63篇 |
建筑科学 | 47篇 |
能源动力 | 68篇 |
轻工业 | 108篇 |
水利工程 | 1篇 |
石油天然气 | 4篇 |
无线电 | 414篇 |
一般工业技术 | 436篇 |
冶金工业 | 229篇 |
原子能技术 | 28篇 |
自动化技术 | 326篇 |
出版年
2023年 | 7篇 |
2022年 | 20篇 |
2021年 | 21篇 |
2020年 | 25篇 |
2019年 | 25篇 |
2018年 | 48篇 |
2017年 | 46篇 |
2016年 | 46篇 |
2015年 | 51篇 |
2014年 | 72篇 |
2013年 | 185篇 |
2012年 | 102篇 |
2011年 | 131篇 |
2010年 | 119篇 |
2009年 | 120篇 |
2008年 | 127篇 |
2007年 | 108篇 |
2006年 | 77篇 |
2005年 | 73篇 |
2004年 | 64篇 |
2003年 | 73篇 |
2002年 | 48篇 |
2001年 | 48篇 |
2000年 | 56篇 |
1999年 | 68篇 |
1998年 | 105篇 |
1997年 | 51篇 |
1996年 | 46篇 |
1995年 | 43篇 |
1994年 | 37篇 |
1993年 | 30篇 |
1992年 | 17篇 |
1991年 | 24篇 |
1990年 | 13篇 |
1989年 | 24篇 |
1988年 | 18篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 8篇 |
1983年 | 13篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1974年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有2312条查询结果,搜索用时 15 毫秒
21.
Itoh K.-I. Watanabe S. Shih J.-S. Sato T. 《Vehicular Technology, IEEE Transactions on》2002,51(6):1460-1468
The performance of a proposed handoff algorithm based on both the distance of a mobile station to neighboring base stations and the relative signal strength measurements is evaluated. The algorithm performs handoff when the measured distance from the serving base station exceeds that from the candidate base station by a given threshold and if the measured signal strength of the adjacent base station exceeds that of the serving base station by a given hysteresis level. The average handoff delay and average number of handoffs are used as criteria for performance. Numerical results are presented to demonstrate the feasibility of the distance-based handoff algorithm, including results for an additional criterion based on relative signal strength. The proposed algorithm is compared with an algorithm based on absolute and relative signal strength measurements and with a solely distance-based algorithm. It is found that the proposed handoff algorithm performs well in a log-normal fading environment when the distance estimate error is modeled by wide-sense stationary additive white Gaussian noise. 相似文献
22.
Wang X.M. Wu-Sheng Lu Antoniou A. 《IEEE transactions on circuits and systems. I, Regular papers》2005,52(5):1021-1031
Multiuser detectors for direct-sequence code-division multiple-access (DS-CDMA) systems based on a recursive convex programming (RCP) relaxation approach are proposed. In these detectors, maximum likelihood (ML) detection is carried out in two steps: first, the combinatorial problem associated with ML detection is relaxed into a convex programming problem and then a recursive approach is applied to get an approximate solution for ML detection. Computer simulations demonstrate that the bit-error rate performance offered by the new detectors is near-optimal and superior to that offered by many existing suboptimal detectors including some recently proposed semidefinite-programming relaxation (SDPR) detectors. In addition, the amount of computation required by the RCP detectors is much less than that required by SDPR detectors. 相似文献
23.
Minchen Chang Jengping Lin Chao-Sung Lai Ruey-Dar Chang Shih S.N. Mao-Ying Wang Lee P.-I. 《Electron Devices, IEEE Transactions on》2005,52(4):484-491
Data retention degradation of a 256-Mbit DRAM during the packaging process is investigated in this paper. Electrical measurement and device simulation show that a trap-assisted leakage degrades the retention time even in packaging process at about 250/spl deg/C. Retention time of the degraded chip is strongly dependent on the negative wordline voltage and operation temperature, but less sensitive to the substrate bias. Trap-assisted gate induced drain leakage is proposed as the mechanism of retention loss in the degraded chip. The degraded chips usually can be repaired by another thermal baking process. We propose Si-H bond breaking and the subsequent trap generation at the gate and drain overlap region as the root cause of retention degradation according to the fact that the Si-H bond density of backend passivation oxide and nitride layers correlate well with the retention performance of DRAM chips with negative wordline bias. Moreover, the packaged chip shows variable retention behavior during a thermal baking of 250/spl deg/C. Theoretical calculation indicates that the trap generation or movement to the high electrical field region beneath the gate can increase the trap-assisted gate induced drain leakage by about an order of magnitude. 相似文献
24.
25.
Fu-Chien Chiu Wen-Chieh Shih Joseph Ya-min Lee Huey-Liang Hwang 《Microelectronics Reliability》2007,47(4-5):548
MOSFETs and MOSCs incorporating HfO2 gate dielectrics were fabricated. The IDS–VDS, IDS–VGS, gated-diode and C–V characteristics were investigated. The subthreshold swing and the interface trap density were obtained. The surface recombination velocity and the minority carrier lifetime in the field-induced depletion region measured from the gated diodes were about 2.73 × 103 cm/s and 1.63 × 10−6 s, respectively. The effective capture cross section of surface state was determined to be 1.6 × 10−15 cm2 using the gated-diode technique in comparison with the subthreshold swing measurement. A comparison with conventional MOSFETs using SiO2 gate oxide was also made. 相似文献
26.
Yu-Pao Tsai Cheng-Hung Ko Yi-Ping Hung Zen-Chung Shih 《IEEE transactions on image processing》2007,16(10):2607-2616
Image-based rendering has been successfully used to display 3-D objects for many applications. A well-known example is the object movie, which is an image-based 3-D object composed of a collection of 2-D images taken from many different viewpoints of a 3-D object. In order to integrate image-based 3-D objects into a chosen scene (e.g., a panorama), one has to meet a hard challenge--to efficiently and effectively remove the background from the foreground object. This problem is referred to as multiview images (MVIs) segmentation. Another task requires MVI segmentation is image-based 3-D reconstruction using multiview images. In this paper, we propose a new method for segmenting MVI, which integrates some useful algorithms, including the well-known graph-cut image segmentation and volumetric graph-cut. The main idea is to incorporate the shape prior into the image segmentation process. The shape prior introduced into every image of the MVI is extracted from the 3-D model reconstructed by using the volumetric graph cuts algorithm. Here, the constraint obtained from the discrete medial axis is adopted to improve the reconstruction algorithm. The proposed MVI segmentation process requires only a small amount of user intervention, which is to select a subset of acceptable segmentations of the MVI after the initial segmentation process. According to our experiments, the proposed method can provide not only good MVI segmentation, but also provide acceptable 3-D reconstructed models for certain less-demanding applications. 相似文献
27.
Hsin-Hung Cho Chin-Feng Lai Timothy K. Shih Han-Chieh Chao 《Mobile Networks and Applications》2016,21(5):846-855
A mature cloud system needs a complete resource allocation policy which includes internal and external allocation. They not only enable users to have better experiences, but also allows the cloud provider to cut costs. In the other words, internal and external allocation are indispensable since a combination of them is only a total solution for whole cloud system. In this paper, we clearly explain the difference between internal allocation (IA) and external allocation (EA) as well as defining the explicit IA and EA problem for the follow up research. Although many researchers have proposed resource allocation methods, they are just based on subjective observations which lead to an imbalance of the overall cloud architecture, and cloud computing resources to operate se-quentially. In order to avoid an imbalanced situation, in previous work, we proposed Data Envelopment Analysis (DEA) to solve this problem; it considers all of a user’s demands to evaluate the overall cloud parameters. However, although DEA can provide a higher quality solution, it requires more time. So we use the Q-learning and Data Envelopment Analysis (DEA) to solve the imbalance problem and reduce computing time. As our simulation results show, the proposed DEA+Qlearning will provide almost best quality but too much calculating time. 相似文献
28.
Chih‐Yung Chang Shih‐Chieh Lee Yu‐Chieh Chen 《Wireless Communications and Mobile Computing》2011,11(6):750-766
A Wireless Mesh Network (WMN) consists of fixed wireless routers, each of which provides service for mobile clients within its coverage area and inter‐connects mesh routers to form a connected mesh backbone. Wireless mesh routers are assigned with a channel or a code to prevent collisions in transmission. With a power control mechanism, each router could be assigned with a power level to control connectivity, interference, spectrum spatial reuse, and topology. Assigning high transmitting power level to a router can enhance the network connectivity but may increase the number of neighbors and worsen the collision problem. How to assign an appropriate power level to each router to improve the network connectivity with a constraint of limited channels is one of the most important issues in WMNs. Given a network topology and a set of channels that has been assigned to mesh routers, the proposed channel‐switching mechanism further reassigns each router with a power level and switches channels of routers to optimize both power efficiency and connectivity. A matrix‐based presentation and operations are proposed to respectively identify and resolve the channel switching problems. Simulation study reveals that the proposed mechanisms increase network throughput and provides a variety of route selection, and thus improves the performance of a given WMN. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
29.
Wetting interaction between Sn-Zn-Ag solders and Cu 总被引:4,自引:0,他引:4
The wetting interaction of Sn-(7.1–9)Zn-(0–3)Ag solders with Cu was investigated from 230°C to 300°C. The wetting time, wetting
forces, and activation energy of the wetting reaction were studied. The wetting time decreases with increasing temperature
and increases with Ag content. The wetting force exhibits a disproportional correlation to temperature rise, while no trend
was observed with respect to Ag content. The wetting behavior was ascribed to the interaction between Cu and Zn. The AgZn3 compound was formed at the interface when the solder contains 0.3% Ag and above, while it was formed within the bulk solder
at 2% Ag and above. 相似文献
30.
Arsenic-doped mid-wavelength infrared HgCdTe photodiodes 总被引:1,自引:0,他引:1
M. A. Kinch D. Chandra H. F. Schaake H. -D. Shih F. Aqariden 《Journal of Electronic Materials》2004,33(6):590-595
The recently developed Te-rich, liquid-phase-epitaxy growth technology for low arsenic-doped mid-wavelength infrared (MWIR)
HgCdTe with p-type doping concentrations <1015 cm−3 has enabled the fabrication of n+/p photodiodes using the damage associated with a boron ion implantation. The diode properties are presented and compared
to similar diodes fabricated in p-HgCdTe doped with Group IBs. The attraction of the arsenic-doped diode technology is associated
with the fact that the arsenic resides on the Te sublattice and is immune to the Hg interstitial fluxes that are present in
the diode-formation process. This leads to minimal diode spread, limited primarily to the n+ region and, hence, a potential for use in really high-density infrared focal planes. At the same time, the Hg interstitials
generated in the diode-formation process should purge the photodiode volume of fast diffusing species, resulting in a high-quality,
diode-depletion region devoid of many Shockley-Read recombination centers. These aspects of diode formation in this material
are discussed. 相似文献