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   7848篇
  免费   91篇
  国内免费   2篇
电工技术   26篇
化学工业   180篇
金属工艺   8篇
机械仪表   23篇
建筑科学   31篇
能源动力   21篇
轻工业   304篇
水利工程   3篇
石油天然气   6篇
无线电   137篇
一般工业技术   191篇
冶金工业   6864篇
原子能技术   16篇
自动化技术   131篇
  2022年   10篇
  2021年   9篇
  2019年   18篇
  2018年   15篇
  2017年   12篇
  2016年   23篇
  2015年   9篇
  2014年   13篇
  2013年   52篇
  2012年   36篇
  2011年   46篇
  2010年   22篇
  2009年   30篇
  2008年   50篇
  2007年   57篇
  2006年   55篇
  2005年   58篇
  2004年   66篇
  2003年   49篇
  2002年   51篇
  2001年   33篇
  2000年   25篇
  1999年   214篇
  1998年   2171篇
  1997年   1209篇
  1996年   795篇
  1995年   404篇
  1994年   376篇
  1993年   441篇
  1992年   54篇
  1991年   118篇
  1990年   88篇
  1989年   101篇
  1988年   90篇
  1987年   99篇
  1986年   88篇
  1985年   84篇
  1984年   17篇
  1983年   29篇
  1982年   45篇
  1981年   57篇
  1980年   54篇
  1979年   15篇
  1978年   26篇
  1977年   177篇
  1976年   346篇
  1975年   21篇
  1974年   12篇
  1970年   10篇
  1955年   9篇
排序方式: 共有7941条查询结果,搜索用时 14 毫秒
91.
BACKGROUND: In this study the effects of pulsed electric field (PEF) pretreatment were evaluated during drying and rehydration of carrots. Carrots pretreated with an electric field intensity of 1 kV cm?1 (capacitance 0.5 µF, 20 pulses) or 1.5 kV cm?1 (capacitance 1 µF, 20 pulses) as well as blanched (100 °C, 3 min) carrots were used for the study. Following pretreatment, samples were oven dried at 70 °C and then rehydrated in distilled water (1:30 w/v) at room temperature (24 ± 1 °C). RESULTS: PEF pretreatment increased the drying rate of carrots. However, the rehydration rate of PEF‐pretreated carrots was lower than that of blanched carrots. There were no colour differences between PEF‐pretreated and blanched carrots before drying and after rehydration. In terms of texture, PEF‐pretreated carrots were firmer than blanched carrots. PEF pretreatment reduced the activity of peroxidase by 30–50%, while blanching completely inactivated the enzyme (>95%). CONCLUSIONS: Overall, the results suggest that PEF could be an effective pretreatment during drying and rehydration of carrots. Copyright © 2009 Society of Chemical Industry  相似文献   
92.
93.
An objective of the International Network on Soil Fertility and Fertilizer Evaluation for Rice (INSFFER) network is to field evaluate deep-point placement (urea supergranules) and slow-release (sulfur coated urea) N fertilizers in irrigated rice. These N sources were compared for performance with split application of prilled urea at 19 sites in Asia in wet season 1981.SCU or USG differed significantly in response curves from prilled urea at 12 of the 17 sites where N response was observed. Over these 17 sites, 22–25% less N as SCU or 29–31% less N as USG provided the same yield increment as the comparatively higher level of N as prilled urea.High profit N rates were derived for 5 sites. The optimal N levels for SCU or USG were less than for prilled urea. However, in one case for both test materials prilled urea was more profitable than SCU or USG. The marginal rates of return of using SCU or USG as opposed to OPU were calculated for the 11 sites where the response functions of the test materials differed significantly from prilled urea. In other than 2 sites for SCU the MRR exceeded 2.0 for 29 and 58 kg N ha–1, indicating the general profitability of these materials when compared to prilled urea.  相似文献   
94.
95.
Aflatoxins are secondary metabolites produced by species of Aspergilli, specifically Aspergillus flavus and Aspergillus parasiticus. These molds are ubiquitous in nature and grow on a variety of substrates, thereby producing aflatoxins. Aflatoxins are of great concern due to their biochemical and biological effects on living organisms. In this article, the occurrence of aflatoxins, their biosynthesis, factors influencing their production, their effects on living organisms, and methods of detection and control in food are reviewed. Future areas of research involving mathematical modeling of factors influencing aflatoxin production and alternative methods of control, such as modified atmosphere packaging, are also discussed.  相似文献   
96.
Salmonella carriage in pigs represents a serious health problem that undoubtedly contributes to the spread of human disease. Thus, the efficient and reliable testing of farm animals for bacteria such as Salmonella is an important aspect of any efficient control strategy. Serological analysis of 15 meat juice samples detected antibodies against Salmonella in some. but not all, of the animals identified bacteriologically as harboring the pathogen, indicating a lack of correlation between the bacteriological and serological methods used for Salmonella detection. The results suggest that testing by enzyme-linked immunosorbent assay is appropriate at the herd level, with culture methods preferable for individual animal analysis. A novel culture protocol detected Salmonella in the cecal contents of 15 pigs, whereas a method based on the European Standard identified only 9 pigs as being Salmonella-positive. During the study, an unusual finding was the relatively high incidence of Salmonella London carriage in the pigs tested.  相似文献   
97.
98.
The effect of ethanol on the foaming properties of beer protein fractions was studied using a microconductivity method and nitrogen gas to generate the foam. Increasing the ethanol concentration resulted in a decrease in foam stability. Interfacial studies including thin film drainage and dilational elasticity measurements indicated that ethanol reduced the rigidity of the adsorbed protein layer resulting in accelerated drainage from the foam lamellae and increased probability of film rupture. These results conflict with data from the Rudin method (using nitrogen gas to generate the foam) which indicate that, at low concentration, ethanol improves foam stability. These apparently conflicting results may be explained by the foam positive effects of a decline in bubble size and increase in bulk viscosity observed for the Rudin method, contrasted with the negative influence of a reduction in surface viscosity observed for the microconductivity foam assessment method.  相似文献   
99.
Using a sensitive direct gas analysis technique, an attempt was made to detect hydrogen evolution from copper corroding in neutral oxygen free chloride solutions. No hydrogen was detected at evolution rates 3 orders of magnitude lower than those reported for copper in pure water.  相似文献   
100.
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