首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   272篇
  免费   19篇
  国内免费   1篇
电工技术   6篇
综合类   3篇
化学工业   107篇
金属工艺   3篇
机械仪表   1篇
建筑科学   22篇
能源动力   5篇
轻工业   41篇
无线电   6篇
一般工业技术   54篇
冶金工业   33篇
原子能技术   2篇
自动化技术   9篇
  2023年   1篇
  2022年   8篇
  2021年   15篇
  2020年   6篇
  2019年   3篇
  2018年   7篇
  2017年   6篇
  2016年   12篇
  2015年   13篇
  2014年   6篇
  2013年   20篇
  2012年   17篇
  2011年   20篇
  2010年   19篇
  2009年   12篇
  2008年   14篇
  2007年   17篇
  2006年   9篇
  2005年   16篇
  2004年   8篇
  2003年   9篇
  2002年   3篇
  2001年   4篇
  2000年   2篇
  1999年   2篇
  1998年   7篇
  1997年   4篇
  1996年   2篇
  1995年   4篇
  1994年   1篇
  1993年   3篇
  1992年   2篇
  1988年   1篇
  1987年   1篇
  1983年   2篇
  1982年   1篇
  1981年   2篇
  1979年   4篇
  1977年   1篇
  1974年   2篇
  1959年   1篇
  1940年   1篇
  1939年   1篇
  1937年   1篇
  1934年   2篇
排序方式: 共有292条查询结果,搜索用时 15 毫秒
71.
72.
According to most models of speech production, the planning of spoken words involves the independent retrieval of segments and metrical frames followed by segment-to-frame association. In some models, the metrical frame includes a specification of the number and ordering of consonants and vowels, but in the word-form encoding by activation and verification (WEAVER) model (A. Roelofs, 1997), the frame specifies only the stress pattern across syllables. In 6 implicit priming experiments, on each trial, participants produced 1 word out of a small set as quickly as possible. In homogeneous sets, the response words shared word-initial segments, whereas in heterogeneous sets, they did not. Priming effects from shared segments depended on all response words having the same number of syllables and stress pattern, but not on their having the same number of consonants and vowels. No priming occurred when the response words had only the same metrical frame but shared no segments. Computer simulations demonstrated that WEAVER accounts for the findings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
73.
BACKGROUND: Heat shock has been associated with the acquisition of tolerance to a wide variety of stressful conditions, including ischemia. This is partly mediated by the production of various heat shock proteins (HSP), including HSP70. One novel approach to the reduction of ischemia-reperfusion injury after lung transplantation is the induction of HSP70 by heat pretreatment of the donor. The purpose of this study was to investigate the feasibility of this approach in an animal model of lung transplantation. METHODS: Animals were divided into six main groups, with groups I to III representing transplanted animals: In groups I and II, donor animals were anesthetized and then underwent heat stress 6 and 12 hours before organ harvest, respectively. Control animals underwent general anesthesia but no heat stress. After harvest, left lungs from groups I to III were preserved for 18 hours at 40 degrees C and then implanted into isogeneic recipients, which were killed 24 hours after reperfusion to assess graft function. Group IV and V animals underwent heat stress followed by a recovery period of 6 and 12 hours, respectively. Lungs were collected both at the time of harvest (right lungs) and after 18 hours of cold preservation (left lungs). Group VI served as nontransplanted controls. Groups IV to VI did not undergo lung transplantation. RESULTS: At the time of harvest but before implantation, HSP70 was significantly increased in heat-shocked nontransplanted donor lungs (groups IV and V) compared with group VI controls. After 18 hours of cold preservation, HSP70 levels were higher in group IV compared with group V and group VI controls. At 24 hours after reperfusion, mean arterial oxygenation was significantly higher in group I compared with group II and group III controls (290.25+/-24.5 vs 154.5+/-23.9 and 119.6+/-11.3 mm Hg, respectively; P < .001). Myeloperoxidase activity was improved in group I compared with group III controls (0.048+/-0.018 vs 0.137+/-0.036 deltaOD/mg/min, respectively; P < .05). The wet/dry weight ratio was also improved in group I compared with group III controls (6.2+/-0.3 vs. 7.8+/-0.4, respectively; P < .05). CONCLUSIONS: Heat pretreatment of the donor 6 hours before harvest results in increased synthesis of HSP70, which offers a dramatic protective effect against subsequent ischemia-reperfusion injury in the lung isograft.  相似文献   
74.
Two incompatible pictures compete for perceptual dominance when they are presented to one eye each. This so-called binocular rivalry results in an alternation of dominant and suppressed percepts. In accordance with current theories of emotion processing, the authors' previous research has suggested that emotionally arousing pictures predominate in this perceptual process. Three experiments were run with pictures of emotional facial expressions that are known to induce emotions while being well controlled in terms of physical characteristics. In Experiment 1, photographs of emotional and neutral facial expressions were presented of the same actor to minimize physical differences. In Experiment 2, schematic emotional expressions were presented to further eliminate low-level differences. In Experiment 3, a probe-detection task was conducted to control for possible response-biases. Together, these data clearly demonstrate that emotional facial expressions predominate over neutral expressions; they are more often the first percept and they are perceived for longer durations. This is not caused by physical stimulus properties or by response-biases. This novel approach supports that emotionally significant visual stimuli are preferentially perceived. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
75.
This study explores boundary-crossing networks in fuel-cell science and technology. We use the case of Norwegian fuel cell and related hydrogen research to explore techno-science networks. Standard bibliometric and patent indicators are presented. Then we explore different types of network maps — maps based on co-authorship, co-patenting and co-activity data. Different network configurations occur for each type of map. Actors reach different levels of prominence in the different maps, but most of them are active both in science and technology. This illustrates that to appreciate fully the range of science-technology interplay, all three analyses need to be taken into account.  相似文献   
76.
Certain cellulose samples, especially those of higher molecular weight, are initially insoluble in N,N-dimethylacetamide (DMAc, 1)/lithium chloride, which is a very common solvent system for cellulosic materials. According to a common protocol, heating or refluxing these samples in DMAc, or in DMAc containing dissolved LiCl, represents one of several so-called ‘activation’ procedures, which are aimed at facilitating subsequent dissolution. In the present work, it is shown that the improved solubility achieved by this method is not only caused by a better activation or improved accessibility of the pulp, but also by a progressing degradation of the cellulosic material (DP loss).The degradation of cellulose in DMAc or DMAc/LiCl is due to two separate chemical processes. The first one, involving N,N-dimethylacetoacetamide (2) which is the primary condensation product of DMAc, causes a slow degradation by thermal endwise peeling. The glucose units peeled off the reducing end are released as furan structures (3). The mechanism appears to be a thermal cleavage of the glycosidic bond, which becomes quite selective towards the proximal anhydroglucose unit by a neighbor group-assisted effect according to quantum-chemical calculations. Due to its stepwise and thus slow mechanism, this pathway contributes only insignificantly to the overall cellulose degradation.The second degradation mechanism causes random chain cleavage and thus pronounced and rather fast changes in the molecular weight distribution. It involves N,N-dimethylketeniminium ions (5), whose presence in DMAc/LiCl at temperatures above 80 °C—the coalescence temperature of DMAc as determined by dynamic NMR—was unambiguously demonstrated by specific trapping in a thermal [2+2]-cycloaddition with lipophilic olefins. The keteniminium ion is an extremely reactive electrophile, which is able to directly cleave glycosidic bonds. The detrimental effect of this intermediate on the integrity of cellulosic pulps was confirmed by addition of an external degrading agent of the keteniminium type. Also the precursor compound, a ketene aminal, was confirmed to be present in heated DMAc or DMAc/LiCl by trapping with allyl alcohol in a spontaneous Claisen-type rearrangement.  相似文献   
77.
The development of a microfluidic biosensor with fluorescence detection for the rapid, sensitive, and serotype-specific detection of Dengue virus is presented. The biosensor chip consists of poly(dimethylsiloxane) (PDMS) substrate with fabricated microchannels and a glass substrate used to seal the microchannels. These two substrates are packaged within a pressure-closed Plexiglas housing to provide a watertight reversible sealing at the PDMS-glass interface. The ability to reversibly seal the device permits easy disassembly and quick interchange of the device parts, which is ideal for developmental purposes. The biosensor employs a magnetic bead-based sandwich hybridization system in conjugation with liposome amplification for the specific detection of nucleic acids. The concentrations of the various biosensor components were optimized using a synthesized fragment of Dengue virus RNA. To evaluate the sensitivity of the assay, two detection systems, based on fluorescence measurements of intact and lysed liposomes, were analyzed. The entire analysis was complete within 20 min (including incubation time) with RNA detection limits of 0.125 nM and 50 pM for intact and lysed liposome detection systems, respectively. Subsequently, the biosensor was applied to the analysis of actual RNA obtained from Dengue virus serotypes 1-4. The resulting signals were compared to those obtained using standard electrochemiluminescence detection and shown to correspond perfectly with respect to serotype identification.  相似文献   
78.
The nuclear reactor has established itself as a future major supplier of electrical energy. The industrial market for other forms of energy, however, is almost as large and represents a new potential for the use of nuclear reactors. The high temperature gas-cooled reactor (HTGR) has been developed for commercial application in the electric power generation field. Since the HTGR is capable of delivering process heat in the temperature range of 1000–1500°F, it has many applications that would not be possible at the lower operating temperatures of water-cooled reactors. This paper briefly summarizes the development of the HTGR and outlines its salient technical features. Modifications to the reactor that enable it to be used as a process heat source are discussed. Specific applications are developed for coal gasification, steelmaking, and hydrogen production.  相似文献   
79.
The combination of nuclear breeder reactors and thermal converters can efficiently utilize uranium and thorium reserves and is a worldwide energy source which is potentially 20 times greater than coal. The very high temperature reactor (VHTR), a thermal converter, can be coupled to open and closed cycle processes to produce hydrogen in large quantities. Current work in the U.S. is focused on the design of a VHTR of about 850 MW(t). The thermal rating and the design are similar to those of the steam cycle Fort St Vrain (FSV) reactor built in Colorado, U.S., but an intermediate helium circuit and a core outlet temperature of 925–950°C are used. Hydrogen production using this reactor would be approximately 10 kg/sec with a carbon-based process or 3 kg/sec with a closed-loop thermochemical process.  相似文献   
80.
In chronic inflammatory diseases the anti-inflammatory effect of glucocorticoids (GCs) is often decreased, leading to GC resistance. Inflammation is related with increased levels of reactive oxygen species (ROS), leading to oxidative stress which is thought to contribute to the development of GC resistance. Plant-derived compounds such as flavonoids are known for their ability to protect against ROS. In this exploratory study we screened a broad range of food-derived bioactives for their antioxidant and anti-inflammatory effects in order to investigate whether their antioxidant effects are associated with the ability to preserve the anti-inflammatory effects of cortisol. The anti-inflammatory potency of the tested compounds was assessed by measuring the oxidative stress–induced GC resistance in human macrophage-like cells. Cells were pre-treated with H2O2 (800 µM) with and without bioactives and then exposed to lipopolysaccharides (LPS) (10 ng/mL) and cortisol (100 nM). The level of inflammation was deducted from the concentration of interleukin-8 (IL-8) in the medium. Intracellular oxidative stress was measured using the fluorescent probe 2′,7′-dichlorofluorescein (DCFH). We found that most of the dietary bioactives display antioxidant and anti-inflammatory action through the protection of the cortisol response. All compounds, except for quercetin, revealing antioxidant activity also protect the cortisol response. This indicates that the antioxidant activity of compounds plays an important role in the protection of the GC response. However, next to the antioxidant activity of the bioactives, other mechanisms also seem to be involved in this protective, anti-inflammatory effect.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号