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In addition to being the single greatest known environmental cause of cancer, cigarette smoke (CS) is also a major contributor to heart disease. We reported previously that 1) inhalation of either mainstream or sidestream CS promotes aortic arteriosclerotic plaque development; 2) 1,3 butadiene, a vapor-phase component of CS, promotes plaque development at 20 ppm, which at the time was only 2 times higher than the threshold limit value; and 3) individual tar fraction carcinogens in CS, including polynuclear aromatic hydrocarbons (PAHs) and nitrosamines, either do not promote plaque development or do so only at high concentrations. These results suggested that the tar fraction is not the primary source of plaque-promoting agents in CS. We asked whether repeated exposure to the tar fraction of CS, collected in a cold trap (TAR), promotes plaque development in an avian model of arteriosclerosis. Acetone extracts of mainstream CS tar from burning, unfiltered reference cigarettes were solubilized in dimethyl sulfoxide (DMSO) and injected weekly into cockerels for 16 weeks (25 mg/kg/week). Positive controls were injected weekly with the synthetic PAH carcinogen, 7,12 dimethylbenz(a)anthracene (DMBA) dissolved in DMSO and negative controls were injected with DMSO. Plaque location and prevalence did not differ from group to group. Morphometric analysis of plaque cross-sectional areas showed that plaque sizes, which are log-normally distributed, were significantly larger in the DMBA cockerels compared to both the TAR and DMSO groups. There were no significant differences in plaque size between DMSO and TAR cockerels. The results reported here, combined with other recent findings, support the conclusion that the primary arteriosclerotic plaque-promoting components of CS are in the vapor phase.  相似文献   
164.
本文报告一种能将FSM自动转换为SDL描述的SDL描述生成器-SDL-TRAN。除了自动变换部分之外,SDL-TRAN还包含一个具有友好用户接口的图形编辑器。  相似文献   
165.
We explore charge-trapping effects in cryogenic particle detectors composed of single-crystal silicon substrates with both titanium transition-edge sensors (TES) and charge-collection electrodes deposited upon them. These effects include transients on various time scales which follow the evolution of different kinds of space charge, intrinsic gain and linearity shifts in signals characteristic of changes in the absorption of energy carried by electrons and holes, variations in charge-collection efficiency and ionization resolution, etc., The physics involved, relevant for many other cryogenic, semiconductor-based devices, includes a variety of charge trapping and transport mechanisms.  相似文献   
166.
高类金属含量非晶态合金的晶化温度研究   总被引:1,自引:0,他引:1  
研究了含有B、Si二种类金属元素的Ni基非晶态合金的晶化温度随其中活性较强的类金属元素B含量变化关系。发现当B含量<17.5at%时,出现二个晶化温度Tcr1和Tcr2;当B含量>17.5at%时,则只有一个晶化温度Tct。利用“双层单元结构模型”和“结构缺陷形成机制”,对其微观机理给出的理论模型解释。  相似文献   
167.
The sialidase inhibitor 4-guanidino-2,4-dideoxy-2,3-dehydro-N-acetylneuraminic acid (4-guanidino-Neu5Ac2en), designed with computer assistance and knowledge of the crystal structure of influenza virus neuraminidase, has shown antiviral effects in animal models of human influenza (M. von Itzstein et al., Nature, 363, 418-423, 1993). Here we demonstrate that the compound efficiently inhibits the enzyme activity of all nine subtypes of avian influenza A neuraminidase in vitro. When administered intranasally to chickens infected with lethal viruses, high doses of the compound (1000 micrograms/kg) protected 85% of birds harboring A/Chick/Victoria/1/85 (H7N7), a fowl plague virus, but not chickens infected with other highly virulent viruses of the N1, N2, or N3 subtype. This differential inhibitory effect was also seen in a plaque reduction assay with Madin-Darby canine kidney cells (MDCK), where 4-guanidino-Neu5Ac2en was more effective against A/Chick/Vic/85 (H7N7) than A/FPV/Rostock/34 (H7N1). In contrast to the substantial plaque reduction observed in MDCK cells, the drug failed to inhibit plaque formation in chicken embryo fibroblasts infected with either A/Chick/Vic/85 or A/FPV/Rostock/34, regardless of its concentration. The different levels of drug efficacy seen in two cell systems most likely reflect the location of virus budding and release in polarized versus nonpolarized cells, as well as the compound's mode of extracellular action.  相似文献   
168.
Experiments to produce polycarbosilazane resin and high-strength silicon carbide–silicon nitride (SixNyCz) fibers as well as resin/fiber characteristics are reported. Polycarbosilazane resin was drawn into fibers from the melt and subsequently treated and pyrolyzed into SixNyCz fibers. These materials are characterized by high tensile modulus (29 × 106 psi for 0.4-mil diameter) and high electrical resistivity (6.9 × 108 Ω·cm for 0.6-mil diameter).  相似文献   
169.
A follow-up study was conducted of clients who stopped attending 4 family planning clinics in Washington County, Oregon, a predominantly white, middle-class suburban community. Clients had enrolled in the program between 1971-74, and dropped out by April 1975. 29% of the women (746) who were overdue for a return visit by more than 3 months (i.e. inactive clients) were contacted by phone and mail. No significant social or demographic differences were found between active and inactive clients or between dropouts who were contacted and those who were not. 71% of all program enrollees dropped out by the end of 3 years. However, 90% of the sample were either using contraception or not at risk of an unwanted pregnancy for a variety of reasons. The remaining 10% were either unprotected or already pregnant with an unplanned pregnancy (2%). The women at risk and not using contraception were more likely to be young, poorly educated, single, and recent enrollees in the family planning program. No other social or economic differences affected the comparison of the 2 groups. Most users continued to use the same method of contraception they had used before. However, a significantly smaller proportion of women were using the pill, a slightly larger proportion were using IUD and 6% more clients were sterilized. The most common reasons for leaving the program were the decision to use a private physician and relocation. Among women at risk, the most common reason was worry about the contraceptive method, especially the pill. New sources of care included private physicians (71%, but 1/3 of these women were disatisfied with their doctors' care or fees), public health clinic not part of the family planning program (21%) and drugstores. A very few women reported no alternate source of care.  相似文献   
170.
Virtual environments (VEs) are extensively used in training but there have been few rigorous scientific investigations of whether and how skills learned in a VE are transferred to the real world. This research aimed to measure and evaluate what is transferring from training a simple sensorimotor task in a VE to real world performance. In experiment 1, real world performances after virtual training, real training and no training were compared. Virtual and real training resulted in equivalent levels of post-training performance, both of which significantly exceeded task performance without training. Experiments 2 and 3 investigated whether virtual and real trained real world performances differed in their susceptibility to cognitive and motor interfering tasks (experiment 2) and in terms of spare attentional capacity to respond to stimuli and instructions which were not directly related to the task (experiment 3). The only significant difference found was that real task performance after training in a VE was less affected by concurrently performed interference tasks than was real task performance after training on the real task. This finding is discussed in terms of the cognitive load characteristics of virtual training. Virtual training therefore resulted in equivalent or even better real world performance than real training in this simple sensorimotor task, but this finding may not apply to other training tasks. Future research should be directed towards establishing a comprehensive knowledge of what is being transferred to real world performance in other tasks currently being trained in VEs and investigating the equivalence of virtual and real trained performances in these situations.  相似文献   
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