全文获取类型
收费全文 | 843篇 |
免费 | 27篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 18篇 |
综合类 | 10篇 |
化学工业 | 90篇 |
金属工艺 | 20篇 |
机械仪表 | 26篇 |
建筑科学 | 12篇 |
矿业工程 | 16篇 |
能源动力 | 10篇 |
轻工业 | 42篇 |
水利工程 | 4篇 |
石油天然气 | 5篇 |
武器工业 | 1篇 |
无线电 | 123篇 |
一般工业技术 | 82篇 |
冶金工业 | 309篇 |
原子能技术 | 20篇 |
自动化技术 | 91篇 |
出版年
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 4篇 |
2018年 | 21篇 |
2017年 | 11篇 |
2016年 | 9篇 |
2015年 | 13篇 |
2014年 | 9篇 |
2013年 | 33篇 |
2012年 | 20篇 |
2011年 | 32篇 |
2010年 | 24篇 |
2009年 | 16篇 |
2008年 | 27篇 |
2007年 | 37篇 |
2006年 | 18篇 |
2005年 | 36篇 |
2004年 | 21篇 |
2003年 | 20篇 |
2002年 | 19篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 19篇 |
1998年 | 89篇 |
1997年 | 50篇 |
1996年 | 50篇 |
1995年 | 27篇 |
1994年 | 21篇 |
1993年 | 24篇 |
1992年 | 6篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 13篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 30篇 |
1974年 | 3篇 |
1970年 | 5篇 |
排序方式: 共有879条查询结果,搜索用时 109 毫秒
61.
Accurate segmentation of foreground objects in video scenes is critical for assuring reliable performance of vision systems
for object tracking and situational awareness in outdoor scenes. Most existing techniques for background modeling and shadow
suppression require that a number of parameters be “hand-tuned” based on environmental conditions. This paper presents two
contributions to overcome such limitations. First, we develop and demonstrate a satellite imagery based approach for selecting
appropriate background and shadow models. It is shown that the illumination conditions (i.e. cloud cover) of a scene can be
reliably inferred from visible satellite images in the local region of the camera. The second contribution presented in the
paper is introduction and evaluation of a Hybrid Cone-Cylinder Codebook (HC3) model which combines an adaptive efficient background
model with HSV-color space shadow suppression into a single coherent framework. The structure of the HC3 model allows for
seamless fusion of the satellite data. We are thereby able to exploit the fact that, for example, shadows are more pronounced
on sunny days than cloudy days, allowing for more sensitive detection. The paper presents a set of experiments using day long
sequences of videos from an operational surveillance system testbed. Results of these experimental analyses quantitatively
illustrate the benefits of using satellite imagery to inform and adaptively adjust background and shadow modeling. 相似文献
62.
Driver behavioral cues may present a rich source of information and feedback for future intelligent advanced driver-assistance systems (ADASs). With the design of a simple and robust ADAS in mind, we are interested in determining the most important driver cues for distinguishing driver intent. Eye gaze may provide a more accurate proxy than head movement for determining driver attention, whereas the measurement of head motion is less cumbersome and more reliable in harsh driving conditions. We use a lane-change intent-prediction system (McCall et al., 2007) to determine the relative usefulness of each cue for determining intent. Various combinations of input data are presented to a discriminative classifier, which is trained to output a prediction of probable lane-change maneuver at a particular point in the future. Quantitative results from a naturalistic driving study are presented and show that head motion, when combined with lane position and vehicle dynamics, is a reliable cue for lane-change intent prediction. The addition of eye gaze does not improve performance as much as simpler head dynamics cues. The advantage of head data over eye data is shown to be statistically significant (p < 0.01) 3 s ahead of lane-change situations, indicating that there may be a biological basis for head motion to begin earlier than eye motion during "lane-change"-related gaze shifts. 相似文献
63.
64.
JM Bhatavdekar DD Patel N Ghosh PR Chikhlikar TI Trivedi TP Suthar SS Doctor NG Shah DB Balar 《Canadian Metallurgical Quarterly》1997,40(7):785-790
Lanepitant is a high-affinity, selective neurokinin-1 receptor (NK-1) and is effective in the dural inflammation model of acute migraine. Lanepitant 30, 80, and 240 mg given orally was evaluated in a double-blind, placebo-controlled crossover study to determine its effect in reducing migraine pain and severity of associated symptoms. Outpatients treated four migraine headaches of moderate or severe pain intensity with study drug according to a randomization schedule. They recorded their pain intensity and severity of migraine-associated symptoms at 30, 60, 90, and 120 min. Although 53 patients were randomly allocated to a treatment sequence, only 40 patients completed all treatments. There was no statistically significant difference in improvement in migraine pain at any time for any of the treatments. Additionally, there was no change in severity of migraine-associated symptoms associated with lanepitant therapy. No adverse events could be attributed to lanepitant. Lanepitant was ineffective orally in treating acute migraine in this trial. This may be due to poor bioavailability during a migraine attack. Alternatively, the neurogenic inflammation hypothesis may not apply to migraine. 相似文献
65.
Mean time to failure (MTTF) is an important reliability measure. Previous research is mainly concerned with the MTTF computation of coherent systems. In this paper, we derive equations to calculate the steady-state MTTF for noncoherent systems. Based on the equations, we extend the BDD by adding an intersection edge in each BDD node to efficiently store additional information for MTTF computation of noncoherent systems. A recursive algorithm is developed for MTTF computation using the extended BDD. To accelerate building the extended BDD, a method is proposed to avoid calculating the intersection edge for some nodes by keeping node monotonicity during the BDD construction. We show the efficiency of our algorithm by applying it to some example fault trees, real-life applications, and large fault tree benchmarks. 相似文献
66.
L. M. Fabietti V. Seetharaman R. Trivedi 《Metallurgical and Materials Transactions A》1990,21(4):1299-1310
The effect of a sudden change in cross section on the microstructural development has been investigated by the directional
solidification technique. Experiments have been carried out in a transparent model system of succinonitrile-acetone so that
the dynamical changes in the interface shapes can be monitoredin situ as the interface travels from a region of uniform cross section to a region of sharply reduced cross section. Different experimental
conditions which give rise to initial steady-state planar, cellular, and dendritic interfaces have been investigated. Significant
changes in microstructures have been observed as the interface approaches a sharply reduced cross section. The planar interface
undergoes transitions to cellular and dendritic morphologies as the cross section is reduced, and reverse transitions are
observed as the cross section is then increased gradually to its original value. An initial cellular interface is found to
become dendritic as the cross section is reduced, and again it becomes cellular as the cross section is increased. When the
experimental conditions are designed to give initial dendritic structures, the change in microstructure is found to occur
only when the reduced cross section is of the order of primary dendrite spacing. When the reduced cross section is more than
about 5 times the primary spacing, no appreciable change is observed in the dendritic array which travels across the cross-sectional
change. The dynamical changes in the interface shape and the microstructural transitions that occur with the change in cross
section have been examined quantitatively and discussed.
Formerly with Ames Laboratory 相似文献
67.
68.
Flux enhancement of thin film composite RO membrane by controlled chlorine treatment 总被引:2,自引:0,他引:2
A major stumbling block in polyamide thin film composite RO membrane performance is its incompatibility with chlorine and oxidizing agents. The amide bond of the membrane is highly vulnerable to chlorine attack. Two reactions are possible with chlorine exposure i.e. N-H bond chlorination and/or aromatic ring chlorination. In this way, chlorine may cause degradation/modification in the membrane leading to deterioration in performance.However, low concentration of chlorine up to a certain time may give synergistic effect on membrane and improve its performance. Chlorine solution, if exposed to membrane for certain time gives enhancement in trans-membrane flux of the membrane.The same solution if exposed for more time deteriorates ultra-thin polyamide layer of TFC membrane. Conspicuously, the membrane with poor salt rejection and flux benefited more as compared to the membrane with better performance. In the present study, membranes with different salt rejection and flux were taken and exposed to the inorganic chlorine solution. The inorganic chlorine solutions were made by dissolving sodium hypochlorite in pH buffer. The different solutions were made by varying pH to investigate the pH dependence. The membrane samples were kept in solution for different time durations. The exposure time was monitored and the exposure level was taken in terms of ppm h (ppm chlorine solution exposed to membrane for a fixed time in h). With the same chlorine concentration, effect of varying pH was studied. Spiral wound TFC membrane modules were also subjected to chlorine solution to study its effect. 相似文献
69.
本文探讨了使用MSP430F5xxx实现ETC系统中实时HDLC编解码的方法.MSP430F5xxx是T1公司MSP430家族最新产品序列,采用先进的0.18工艺,1MIPS消耗的电流低到了惊人的160μA.同时,FSxxx产品都配备了高效灵活的DMA模块,对16bit数据进行搬移只需要2个时钟周期. 相似文献
70.
Dyer JA Trivedi P Sanders SJ Scrivner NC Sparks DL 《Environmental science & technology》2003,37(5):923-930
Few studies have demonstrated the practical application of surface complexation models, calibrated with fundamental macroscopic and spectroscopic metal sorption data, in helping to solve industrial trace metal emissions problems. In this work, multistage ferrihydrite sorption systems are evaluated for their effectiveness in reducing single-solute lead(II) [Pb(II)] concentrations in contaminated water streams to very low levels. Experimental data and modeling results indicate that a multistage sorption system can significantly reduce Pb(II) effluent concentrations for the same total amount of sorbent or, alternatively, dramatically lower total sorbent consumption for the same effluent Pb(II) concentration. Model predictions were generated using a steady-state, multistage, equilibrium adsorber model that was specifically developed for and integrated into 0LI Systems' Environmental Simulation Program. The modified triple-layer model was used to simulate Pb(II) surface-liquid equilibria within the adsorber model. Engineering screening evaluations indicate that a 2-3-stage sorption process can provide significant economic savings when compared to a 1-stage process operating with the same target effluent Pb(II) concentration. Additional equilibrium stages beyond 2 or 3 provide diminishing economic returns. The major economic driver for multiple contacting stages is reduced capital investment and operating costs for sludge handling, dewatering, and disposal. 相似文献