全文获取类型
收费全文 | 343篇 |
免费 | 2篇 |
专业分类
电工技术 | 11篇 |
化学工业 | 61篇 |
机械仪表 | 14篇 |
建筑科学 | 4篇 |
能源动力 | 9篇 |
轻工业 | 18篇 |
无线电 | 48篇 |
一般工业技术 | 74篇 |
冶金工业 | 87篇 |
原子能技术 | 2篇 |
自动化技术 | 17篇 |
出版年
2014年 | 3篇 |
2013年 | 8篇 |
2012年 | 4篇 |
2011年 | 6篇 |
2010年 | 4篇 |
2009年 | 8篇 |
2008年 | 13篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 18篇 |
2000年 | 10篇 |
1999年 | 15篇 |
1998年 | 28篇 |
1997年 | 15篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1983年 | 8篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1971年 | 3篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1950年 | 2篇 |
1948年 | 4篇 |
1947年 | 2篇 |
1944年 | 2篇 |
1942年 | 2篇 |
1925年 | 2篇 |
排序方式: 共有345条查询结果,搜索用时 15 毫秒
71.
Visceral pain is a substantial, clinical problem but unfortunately few experimental models are available to study this phenomenon in man. In the present study we inserted a stimulation catheter 5-10 cm into the ileo-sigmoidostomy of nine patients. The catheter contained six small, flexible electrodes separated by 4 mm. The gut was stimulated by single burst, repeated burst (five stimuli delivered at 2 Hz), or continuous burst stimuli (4 Hz for 30, 60, 90, and 120 s). The sensation (ST), pain detection (PDT), and pain tolerance (PTT) thresholds to single/repeated burst stimuli were determined. The location/size/sensitivity of referred pain after repeated/continuous stimulation were characterized. The brain potentials to single burst stimuli and to increasing stimulus intensity were measured. ST to single burst stimuli was easy to determine (8 mA) and to reproduce. The patients found it difficult to determine the PDT and PTT to single burst stimuli, however both thresholds were easily determined for repeated burst stimuli. The pain thresholds to single burst stimuli were twice as high as the thresholds to repeated burst stimuli, indicating the importance of central temporal summation for visceral pain. Minor changes in the stimulus location resulted in changes of the referred pain projection site. The words most frequently selected (78%) from the McGill Pain Questionnaire to describe repeated burst stimulations were shooting, pricking, flashing, and boring. The amplitude of the brain potentials increased at increasing stimulus intensity. A stimulus intensity giving an initial pain rating of around 5 on a 0-10 visual analog scale (VAS) was used for continuous stimulation. A general increase of the pain intensity and the area of referred pain was found during this stimulation. It was concluded that electrical stimulation of the human gut provokes pain and especially long sequences of visceral stimuli are adequate to evoke referred pain mimicking pain profiles of pathologic origin. 相似文献
72.
73.
Power-system generators may experience self-excitation overvoltages due to certain contingencies. In an attempt to derive a novel self-excitation (SE) preventive scheme, the authors describe a prediction system based on pattern-recognition techniques. Several design approaches are explained. A hyperplane discriminant is used to define the predictor surface. An algorithm is developed to reduce the number of telemetered channels required and hence the complexity of the prediction system structure. Moreover, a fast corrective algorithm designed to provide security improvement action is explained. The system studied is the Manitoba Hydro northern AC collector system where SE is the operating problem of concern. The results obtained prove the effectiveness of the proposed prediction scheme 相似文献
74.
Prolonged, severe immunodeficiency provides the necessary milieu for the emergence of anogenital neoplasia caused by human papillomaviruses. Anal neoplasia is likely to become a more common manifestation of HIV disease as patients with profound immunodeficiency, who would have succumbed to opportunistic infections earlier in the epidemic, are now surviving for extended periods of time because of increasingly effective antiretroviral, prophylactic, and antimicrobial therapies. The screening and treatment strategies described for use in HIV-infected patients with anal neoplasia are currently being investigated and refined. 相似文献
75.
Clinical studies have demonstrated that pharmacotherapies may improve alcoholism treatment, when combined with traditional psychosocial therapies. Recently, the opioid antagonist, naltrexone, has been approved as an adjunct in alcoholism treatment, and several other pharmacotherapies for alcoholism are under development. Because of the abstinence orientation of many patients, we assessed attitudes regarding medications, and explored whether alcoholic patients would consider taking medication as part of their alcoholism treatment. Active patients (n = 127) in three alcohol treatment settings were surveyed with an anonymous questionnaire which asked demographics, personal alcoholism history and questions about medication use. They were asked whether they felt disulfiram and naltrexone were helpful for alcoholics and whether they would take the medications. The findings indicate that the patients were divided about the use of pharmacotherapy for the treatment of alcoholism. The strongest predictor of willingness to take medication was a belief that the medication would be helpful. 相似文献
76.
For model-driven engineering (MDE) to become more Agile, the community needs to embrace development and operations (DevOps) practices. One of the core practices of DevOps is the use of pipelines to enable CI/CD to make teams more Agile and break down the barriers between development and operations with faster deployments. Current MDE tooling is not designed at its core to participate in DevOps pipelines. Consequently this makes the adoption of MDE in industry more difficult. In this article, we cover an industrial experience report describing how we enabled our pipelines using DevOps and MDE.
相似文献77.
Airborne depth-resolved laser-induced sea-water Raman-backscatter waveforms have been obtained along a flight line extending westward from a point approximately 30 km seaward of Assateague Island to a point where the beach was intersected at latitude 38.1 degrees N and longitude 75.2 degrees W. Pulses from a 337.1-nm nitrogen laser were repetitively transmitted vertically downward into the water column. The laser-induced water Raman backscatter pulse at 381-nm wavelength was depth (or time) resolved into forty bins having widths of -25 cm each. When converted to along-track profiles, the waveforms reveal cells of decreased Raman backscatter superimposed on an overall trend of monotonically decreasing water column optical transmission. This airborne lidar technique shows potential for (1) rapid, quantitative, synoptic study of the homogeneity of the oceanic water column and (2) measurement of the horizontal spatial distribution of the optical transmission of the upper mixed layer of the ocean. A multiple convolution model of a Gaussian transmitted pulse, Gaussian sea surface height, and slope probability density, together with an exponential-decay water-column impulse response, is shown to qualitatively account for the observed pulse shape. 相似文献
78.
79.
Chalcopyrite electrodes of both natural and synthetic material were cathodically reduced in several acid electrolytes. At current densities below 10mA cm–2 chalcocite was formed and at higher currents the solid product contained elemental copper. The other reduction products were H2S and Fe++. The current efficiency, measured in terms of the Fe++ produced, generally fell with the amount of charge passed, the extent of the decrease depending on current density and the composition and temperature of the electrolyte. The decrease was attributed to evolution of hydrogen on the increasing surface area of the porous solid product as a consequence of inhibition of the chalcopyrite reduction process by ferrous salt precipitated in the pores. At sufficiently low current densities and short periods of electrolysis, chalcopyrite reduction was found to be activation controlled over a three order of magnitude range of currents, with a Tafel slope consistent with a one electron rate-determining step.Presented in part at the 102nd Annual Meeting, AIME, Chicago, 1973. 相似文献
80.
C. E. Swift Sara P. Fore F. G. Dollear 《Journal of the American Oil Chemists' Society》1950,27(1):14-16
- The extraction, processing, characteristics, and stability properties of nine batches of hexane-extracted rice bran oil were investigated. The oils were refined, bleached, and deodorized and their color and stability determined. Samples of the bleached oils were hydrogenated to approximately shortening consistency, deodorized, and the stability of the hydrogenated products determined.
- Pilot plant extractions of five batches of rice bran yielded crude oils equivalent to 91% of the hexane-soluble portions of the bran.
- The nine crude oils whose content of free fatty acids ranged from 2.0 to 6.3% were refined by the cup method with losses ranging from 12.0 to 23.5% although the neutral oil content of six crude rice bran oils ranged from 89.9 to 92.6%.
- The Lovibond color of the nine refined oils ranged from 35 yellow and 4.5 red to 70 yellow and 9.5 red, and the color of the bleached oils ranged from 15 yellow and 1.5 red to 35 yellow and 3.2 red.
- Steam-refining, employed in conjunction with alkali-refining, proved effective as a means of reducing the losses in refining rice bran oil.
- The nine batches of refined, bleached, and deodorized rice bran oils had iodine values ranging from 101.3 to 105.7 and stabilities averaging 24 hours.
- Nine bleached oils hydrogenated to approximate shortening consistency had iodine values averaging approximately 66 and stabilities averaging 370 hours.
- Refined, bleached, and deodorized rice bran oil is bland but has some tendency toward flavor reversion.
- The most outstanding characteristics of rice bran oil is its exceptional stability after hydrogenation.