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   251篇
  免费   9篇
电工技术   3篇
综合类   1篇
化学工业   24篇
金属工艺   1篇
机械仪表   6篇
建筑科学   3篇
能源动力   9篇
轻工业   71篇
水利工程   6篇
无线电   16篇
一般工业技术   43篇
冶金工业   58篇
自动化技术   19篇
  2023年   1篇
  2022年   1篇
  2021年   2篇
  2020年   2篇
  2019年   5篇
  2018年   1篇
  2017年   4篇
  2016年   1篇
  2015年   5篇
  2014年   4篇
  2013年   8篇
  2012年   17篇
  2011年   23篇
  2010年   8篇
  2009年   18篇
  2008年   17篇
  2007年   16篇
  2006年   15篇
  2005年   7篇
  2004年   15篇
  2003年   7篇
  2002年   4篇
  2001年   4篇
  2000年   2篇
  1998年   6篇
  1997年   8篇
  1996年   7篇
  1995年   5篇
  1994年   6篇
  1993年   6篇
  1992年   7篇
  1990年   4篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1986年   3篇
  1983年   3篇
  1982年   2篇
  1981年   4篇
  1979年   1篇
  1977年   2篇
  1976年   1篇
  1975年   1篇
  1973年   1篇
  1970年   1篇
  1964年   1篇
  1962年   1篇
排序方式: 共有260条查询结果,搜索用时 31 毫秒
81.
Five groups of turkeys received C.U. strain Pasteurella multocida vaccine in the drinking water for one day. One group received the 0.1% level of sulfaquinoxaline feed medication at the time of vaccination, while 4 other groups received the feed medication 1, 2, 3 and 4 days after vaccination, respectively. Two weeks after vaccination all groups were exposed to a virulent P-1059 strain of P. multocida by the drinking water route. The results suggest that turkeys on the feed medication at the time of vaccination and possibly those receiving the initial fed medication the next day, failed to experience a satisfactory immunologic response. The possible ill effects of the sulfaquinoxaline feed medication on the duration of the immunity was not determined. A schedule and level of feed medication approved by the Food and Drug Administration was used; namely, 2 days on the 0.1% level, 3 days on a normal ration, and then 2 additional days on the 0.05% level of sulfaquinoxaline feed medication.  相似文献   
82.
Remediation of aquifers containing trichloroethylene (TCE) relies primarily on physical extraction of contaminated groundwater and soil. Unfortunately, this is typically expensive and does not always attain the desired treatment goals. In situ bioremediation via natural attenuation is an alternative treatment process in which TCE is transformed by indigenous microorganisms and plants. In this study, TCE was observed in a surficial aquifer that discharges into a wetland. Experiments were undertaken to determine whether natural attenuation of TCE in the wetland was possible. Microcosms were constructed using sandy soil+/-eastern cottonwoods (Populus deltoides) from the wetland's edge and organic soil+broad-leaved cattails (Typha latifolia) from the wetland's interior. [14C] TCE was added to each microcosm (1.27 microCi). Overtime, 14C was recovered from four microcosm compartments: (1) as 14C bound to soil and water, (2) as volatilized [14C] TCE, (3) as [14C] CO2 produced by mineralization of [14C] TCE, and (4) as 14C incorporated into the plants. Total recoveries of the 14C-label ranged from 73.6% to 95.8%. Volatilized [14C] TCE accounted for the majority ( > 50%) of the recovered label. In microcosms without plants, [14C] CO2 represented 3.2% (organic soil) to 15.6% (sandy soil) of the recovered 14C, indicating that TCE was mineralized by indigenous microorganisms. The presence of the broad-leaved cattail resulted in increased production of [14C] CO2 to 5.3% in the organic soil. The data thus suggest that natural attenuation is a potential bioremediative strategy for TCE-contaminated wetlands.  相似文献   
83.
The modelling of the geometrical structure of a special kind of concrete is discussed. It is a matter of self-flowing refractory castables with spherical grains. The system of hard spheres is compared to several well-established models of spatial statistics and statistical physics as well as to a model used by concrete engineers. It turns out that the structure can be well described by the latter model and a further newly developed model, which is similar to a marked Gibbs process. The result is based on the comparison of common summary statistics like the pair correlation function and the spherical contact distribution function.  相似文献   
84.
Lavie and Tsal (1994) proposed that spare attentional capacity is allocated involuntarily to the processing of irrelevant stimuli, thereby enabling interference. Under this view, when task demands increase, spare capacity should decrease and distractor interference should decrease. In support, Lavie and Cox (1997) found that increasing perceptual load by increasing search set size decreased interference from an irrelevant distractor. In three experiments, we manipulated the cue set size (number of cued locations) independently of the display set size (number of letters presented). Increasing the display set size reduced distractor interference regardless of whether the additional letters were relevant to the task. In contrast, increasing the cue set size increased distractor interference. Both findings are inconsistent with the load explanation, but are consistent with a proposed two-stage dilution account. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
85.
86.
87.
Cells within the body are subject to various forces; however, the details concerning the way in which cells respond to mechanical stimuli are not well understood. We demonstrate that laser‐induced shockwaves (LIS) combined with biosensors based on fluorescence resonance energy transfer (FRET) is a promising new approach to study biological processes in single live cells. As “proof‐of‐concept,” using a FRET biosensor, we show that in response to LIS, cells release intracellular calcium. With the parameters used, cells retain their morphology and remain viable. LIS combined with FRET permits observation of the cells immediate response to a sudden shear force. Microsc. Res. Tech. 78:195–199, 2015. © 2015 Wiley Periodicals, Inc.  相似文献   
88.
Pericarp browning is the main limitation to the postharvest storage, handling and marketing life of litchi fruit. Pre‐storage treatment with pure N2 gas is potentially effective in reducing skin browning and maintaining eating quality of litchis. To better understand inhibition of pericarp browning by a short period of anoxia, adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP) levels, adenylate energy charge and membrane permeability were investigated. Litchi fruit were exposed to pure N2 gas for 6 h and then kept in closed but vented containers for 6 days in the dark at 25 °C and 95–100% relative humidity. Changes in the mentioned fruit physiology and biochemistry parameters and in browning index were measured. ATP concentration and adenylate energy charge decreased rapidly and membrane permeability (relative leakage) increased gradually during storage. Fruit exposed to N2 gas exhibited higher concentrations of ATP, ADP and AMP and adenylate energy charge levels, and lower levels of browning index and membrane permeability, compared to control (non‐N2‐treated) fruit. Greater differences in ATP and ADP concentrations and adenylate energy charge levels of pericarp tissues between N2‐treated and control fruit were more manifest after 4 and 6 days of storage, in association with significant differences at the 5% level in the pericarp browning index. It is suggested that pre‐storage anoxia treatment maintains membrane integrity of pericarp tissues, with high ATP and ADP concentrations and high adenylate energy charge levels. Thus, the loss of cellular compartmentalization (mixing of enzymes and substrates) that leads to enzymatic browning of litchi fruit pericarp is delayed. Copyright © 2007 Society of Chemical Industry  相似文献   
89.
Solar driers that are currently being investigated for drying of agricultural products can be divided into two major divisions, depending upon how they transfer the incident solar energy to the product to be dried. These two divisions are direct and indirect drying, with some work also being done on combination drying procedures. In direct solar driers, the product to be dried is usually either inside a tent, greenhouse, or a glass‐topped box, where the product to be dried is heated by the direct rays from the sun and the moist air is removed by ambient wind movement. These dryers do accelerate moisture loss rate and the product is usually safe from inclement weather. These dryers usually do not require fans for forced air circulation. With indirect drying, the opposite is true, where most require powered fans for forced air circulation. With this type of dryer, both flat‐plate and inflated tube solar heat absorbers are used, with each offering certain advantages. Also, combination dryers have been built that utilize both direct and indirect principles. Product evaluation of solar dried foods indicate that in most cases the physical properties, flavor, and vitamin A and C retention were as good as, or better than, conventional dried foods. The economics of the solar systems indicate that most drying procedures are economically feasible for use in small‐scale operations only, with the exception of grain drying.  相似文献   
90.
The cigarette beetle, Lasioderma serricorne (Fabricius), is the most prevalent pest of stored tobacco and is responsible for substantial economic damage. Other than L. serricorne, few insects have been found to infest tobacco due to its low nutritional value and nicotine toxicity. Self, L.S., Guthrie, F.E., Hodgson, E. [1964a. Metabolism of nicotine by tobacco-feeding insects. Nature 204, 300-301] reported that L. serricorne metabolizes at least 70% of ingested nicotine to cotinine. This study re-examined nicotine metabolism by the L. serricorne using gas chromatography/flame ionization detection (GC/FID) and gas chromatography/thermal desorption with time-of-flight mass spectrometry (GC/TDS/ToF). Cigarette beetles reared on whole-wheat flour were compared with those reared on tobacco. Larvae, depurated larvae, frass, and both diets were analyzed to determine if nicotine was assimilated, sequestered, metabolized, and/or excreted. Contrary to previous findings, these data indicate that L. serricorne does not metabolize a significant amount of nicotine into cotinine. Nicotine is excreted unmodified. Older research involving nicotine metabolism by other insects should be reviewed in the light of these findings.  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