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   117篇
  免费   8篇
化学工业   14篇
机械仪表   1篇
建筑科学   16篇
轻工业   29篇
无线电   8篇
一般工业技术   25篇
冶金工业   14篇
自动化技术   18篇
  2024年   1篇
  2021年   4篇
  2020年   1篇
  2019年   3篇
  2018年   10篇
  2017年   7篇
  2016年   4篇
  2015年   3篇
  2014年   2篇
  2013年   7篇
  2012年   8篇
  2011年   8篇
  2010年   10篇
  2009年   2篇
  2008年   7篇
  2007年   7篇
  2006年   4篇
  2005年   4篇
  2004年   3篇
  2003年   5篇
  2002年   2篇
  2001年   1篇
  2000年   4篇
  1999年   1篇
  1998年   1篇
  1997年   2篇
  1996年   2篇
  1994年   1篇
  1993年   1篇
  1991年   1篇
  1990年   1篇
  1988年   2篇
  1985年   1篇
  1984年   1篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1971年   1篇
排序方式: 共有125条查询结果,搜索用时 0 毫秒
41.
White clover (WC) offers an alternative source of nitrogen (N) for pasture-based systems. Substituting energy- and carbon-intensive synthetic N fertilizers with N derived from biological fixation by WC has been highlighted as a promising environmental mitigation strategy through the omission of emissions, pollutants, and energy usage during the production and application of synthetic fertilizer. Therefore, the objective was to investigate the effect of the inclusion of WC in perennial ryegrass (PRG) swards on the environmental impact of pasture-based dairy systems. Cradle-to-farm gate life cycle assessment of 3 pasture-based dairy systems were conducted: (1) a PRG–WC sward receiving 150 kg of N/ha per year (CL150), (2) a PRG–WC sward receiving 250 kg of N/ha per year (CL250), and (3) a PRG-only sward receiving 250 kg of N/ha per year (GR250). A dairy environmental model was updated with country-specific N excretion equations and recently developed N2O, NH3, and NO3? emission factors. The environmental impact categories assessed were global warming potential, nonrenewable energy, acidification potential, and eutrophication potential (marine and freshwater). Impact categories were expressed using 2 functional units: per hectare and per metric tonne of fat- and protein-corrected milk. The GR250 system had the lowest milk production and highest global warming potential, nonrenewable energy, and acidification potential per tonne of fat- and protein-corrected milk for all systems. The CL250 system produced the most milk and had the highest environmental impact across all categories when expressed on an area basis. It also had the highest marine eutrophication potential for both functional units. The impact category freshwater eutrophication potential did not differ across the 3 systems. The CL150 system had the lowest environmental impact across all categories and functional units. This life cycle assessment study demonstrates that the substitution of synthetic N fertilizer with atmospheric N fixed by WC has potential to reduce the environmental impact of intensive pasture-based dairy systems in temperate regions, not only through improvement in animal performance but also through the reduction in total emissions and pollutants contributing to the environmental indicators assessed.  相似文献   
42.
Abstract: The reported benefits of enrichment of air atmospheres with argon or oxygen for control of enzymatic browning were investigated by determining the effects of these atmospheres on PPO kinetics. Kinetics of purified apple PPO and a commercially available mushroom PPO were studied in an in vitro model system. Enrichment with argon produced greater inhibitory effects than the current industry practice of enrichment with nitrogen. Kmapp values (mM) for apple PPO in 3%O2/97%Ar, 3%O2/97%N2, and air, were 133, 87, and 48, respectively. The data indicate that inhibition by both gases is competitive, and also support the hypothesis that the greater inhibitory effect of argon was proportional to the size of the Van der Waals radius of argon against nitrogen (1.91Å against 1.54Å). Much smaller inhibitory effects were observed in the presence of 80% O2 (Kmapp 57mM), and the nature of this inhibition was less clear. The results suggest that the benefits of argon enrichment may be relatively small, and may require critical enzyme, substrate, and gas levels to be successful. However, these benefits may be exploitable commercially in some fresh‐cut products, and may allow less anoxic atmospheres to be used. Practical Application: Control of enzymatic browning without sulfites continues to be a challenge in some fresh‐cut products. While sporadic benefits of these atmospheres in control of enzymatic browning have been reported, results have been inconsistent in commercial practice. The results suggest that the benefits of argon enrichment may be relatively small, and may require critical enzyme, substrate, and gas levels to be successful. However, these benefits may be exploitable commercially in some fresh‐cut products, and allow less anoxic atmospheres to be used.  相似文献   
43.
44.
45.
A review of the literature in the area of hypnotic dreams suggests that physiological correlates of hypnotic dreams are better established than content characteristics. A study is also reported that examined the content of hypnotic dreams in relation to that of nocturnal dreams and daydreams from the same Ss. Ss were 16 undergraduates divided into deep-trance and medium-trance groups. Deep trance Ss' hypnotic dreams were similar to their nocturnal dreams and different from daydreams on a wide variety of characteristics including length, emotional themes, characters, setting, and amount of distortion. Medium trance Ss' hypnotic dreams were found to fall between their nocturnal dreams and daydreams on most of these measures. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
46.
Limited research has quantified variation in the characteristics of the breasts among women and determined how these breast characteristics are influenced by age and body mass. The aim of this study was to classify the breasts of women in the community into different categories based on comprehensive and objective measurements of the characteristics of their breasts and torsos, and to determine the effect of age and body mass index on the prevalence of these breast categories. Four breast characteristic clusters were identified (X-Large, Very-ptotic & Splayed; Large, Ptotic & Splayed; Medium & Mildly-ptotic; and Small & Non-ptotic), with age and BMI shown to significantly affect the breast characteristic clusters. These results highlight the difference in breast characteristics exhibited among women and how these clusters are affected by age and BMI. The breast characteristic clusters identified in this study could be used as a basis for future bra designs and sizing systems in order to improve bra fit for women.

Practitioner summary: This original research provides evidence for bra designers and manufacturers on the diverse breast characteristics exhibited by women within the population and the significant effect that both body mass index and age have on the breast characteristic clusters. Future bra designs should consider the variation in breast characteristics among women.

Abbreviations: BMI: Body Mass Index; UBCC: Under-bust chest circumference  相似文献   

47.
The occurrence of turbulent flow conditions in the connection tubing or at the entrance of the detection flow cell has been identified as a potential source of excessive detector noise in the signal of the diode array UV-absorption detector flow cell of a commercial HPLC system used to perform high-speed separations on wide-bore columns (4.6 mm i.d.). This excessive noise was found to occur abruptly if the flow rate is increased beyond a certain critical value or during gradient runs, if the mobile phase viscosity falls below a certain critical value. Several detector cells of different dimensions were studied to investigate the dependency of the effect on the detector cell design and the system tubing. Evidence for the turbulent flow origin of this noise is that its onset always occurred at a given fixed value of the Reynolds number. This critical Reynolds number could also be used to predict the onset of detector noise during gradient elution runs. Second, evidence for the turbulent flow origin of the noise was that it could be reliably eliminated using a flow splitter after the column to reduce the flow rate below its critical value before entering the detector. The loss in separation efficiency and detection sensitivity accompanying this flow splitting solution was found to be so small that it does not weigh up against the huge advantage of the possibility to eliminate the excessive detector noise.  相似文献   
48.
Particle linear image velocimetry (PLIV), a novel velocity measurement method for microfluidic characterization, is reported. The method records a series of one-dimensional images that represent the trace of particles in the flow across a one-dimensional imager. Linear imaging results in a faster frame rate than planar imaging, allowing observations at larger magnifications, or the measurement of faster flow in real-time than comparable techniques. In contrast to particle image velocimetry (PIV), PLIV captures fast flow dynamics and does not require high-speed cameras or shutters. Furthermore, PLIV is adaptable to multiple linear imager formats and, as one example, can use laser scanning confocal microscopes (LSCMs) that acquire images slowly, but with high optical sectioning resolutions. A higher spatial resolution can be obtained for flows where the in-plane velocity gradient in the direction of the optical path (z direction) is important. The PLIV algorithm is fully described and its utility is demonstrated by the measurement of: a steady Poiseuille flow with 1-m spatial resolution in a microfluidic environment; dynamic measurement of transient flows with 250-ms temporal resolution; and the simultaneous calculation of particle dimension statistics.  相似文献   
49.
50.
Camelina oil was found to have a much lower Oil Stability Index and higher p-anisidine rates in the oven storage test than either rapeseed or sunflower oils. Stabilization of camelina oil was evaluated with 21 food grade synthetic and natural antioxidants and antioxidant formulations, using both the Oil Stability Index (OSI) and the oven storage test. The Oil Stability Index of camelina oil was able to be increased above that of rapeseed oil with TBHQ and its formulation with citric acid, and above that of sunflower oil with EGC, EGCG, carnosic acid, propyl gallate, rosemary extract with ascorbyl palmitate or with gallic acid. para-Hydroxyphenols were found to be more effective than ortho-hydroxyphenols and monohydroxyphenols had no significant effect on the OSI. Good correlation (R 2 = 0.96) was found between the stabilizing effect of ortho-hydroxyphenols and the molarity of the phenyl hydroxyl groups per weight of antioxidant. The oven storage test carried out with six of the evaluated antioxidants indicated that p-anisidine rates of camelina oil stabilized with commercial formulations of TBHQ with citric acid or rosemary extract with ascorbyl palmitate were about the same as that of sunflower oil, an almost 90% rate reduction when compared to camelina oil. Accordingly, camelina oils stabilized with TBHQ/citric acid and rosemary extract/ascorbyl palmitate formulations were more stable than rapeseed and sunflower oils, respectively in terms of OSI induction times and p-anisidine rates.  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