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   860篇
  免费   40篇
  国内免费   1篇
电工技术   6篇
化学工业   222篇
金属工艺   34篇
机械仪表   32篇
建筑科学   32篇
矿业工程   5篇
能源动力   39篇
轻工业   145篇
水利工程   4篇
石油天然气   5篇
无线电   46篇
一般工业技术   121篇
冶金工业   50篇
原子能技术   3篇
自动化技术   157篇
  2024年   3篇
  2023年   10篇
  2022年   30篇
  2021年   31篇
  2020年   26篇
  2019年   22篇
  2018年   30篇
  2017年   34篇
  2016年   35篇
  2015年   21篇
  2014年   46篇
  2013年   67篇
  2012年   63篇
  2011年   67篇
  2010年   39篇
  2009年   37篇
  2008年   51篇
  2007年   39篇
  2006年   32篇
  2005年   25篇
  2004年   18篇
  2003年   20篇
  2002年   13篇
  2001年   6篇
  2000年   4篇
  1999年   3篇
  1998年   9篇
  1997年   8篇
  1996年   3篇
  1995年   12篇
  1994年   8篇
  1993年   5篇
  1992年   4篇
  1991年   5篇
  1990年   5篇
  1989年   3篇
  1988年   5篇
  1986年   4篇
  1985年   4篇
  1984年   3篇
  1983年   7篇
  1982年   3篇
  1981年   7篇
  1980年   5篇
  1979年   3篇
  1978年   6篇
  1976年   5篇
  1974年   6篇
  1971年   2篇
  1955年   2篇
排序方式: 共有901条查询结果,搜索用时 15 毫秒
11.
An apparatus for measuring the normal spectral emittance (λ = 0.645 μ.) of metals with very high vapor pressures has been designed and used for erbium, dysprosium and samarium at temperatures above 1000 K. The samples are maintained in an argon atmosphere at a pressure slightly above atmospheric pressure. The measured normal spectral emittances are: Erbium, (solid), ∈ = 0.372 ± 0.011; (liquid), ∈ = 0.372 ± 0.011; Dysprosium, (solid), ∈ = 0.631 – 1.889 × 10–4 T (deg K); (liquid), ∈ = 0.297 ± 0.088; Samarium, (solid), ∈ = 0.437 ± 0.030; (liquid, estimated), ∈ = 0.437 ± 0.03. TERRY S. KING, formerly Undergraduate Research Helper. DORAB N. BARIA, formerly NSF Presidential Intern and Post-Doctoral Fellow. Prepared for the Energy Research and Development Administration under Contract No. W-7405-eng-82.  相似文献   
12.
The potentialities for 1-aryl-5-methyl-3-hydroxypyrazoles as intermediates in the field of dyes have been analysed. Some azoic derivatives have been synthesized and both electronic spectra and tinctorial properties on various substrates (wool, nylon, polyester, plasticized PVC) examined. The effect of substituents on the position of the long wavelength absorption maxima is discussed in terms of Hammett σ constants and interesting relationships are obtained. For each application the most important technical properties are assessed and significant fastness to various agents is evaluated.Finally a comparison with properties of similar pyrazol-5-one derivatives is made.  相似文献   
13.
14.
15.
Zinc oxide (ZnO) is an inorganic compound widely used in everyday applications. ZnO is currently listed as a generally recognized as safe (GRAS) material by the Food and Drug Administration and is used as food additive. The advent of nanotechnology has led the development of materials with new properties for use as antimicrobial agents. Thus, ZnO in nanoscale has shown antimicrobial properties and potential applications in food preservation. ZnO nanoparticles have been incorporated in polymeric matrices in order to provide antimicrobial activity to the packaging material and improve packaging properties. This review presents the main synthesis methods of ZnO nanoparticles, principal characteristics and mechanisms of antimicrobial action as well as the effect of their incorporation in polymeric matrices. Safety issues such as exposure routes and migration studies are also discussed.  相似文献   
16.
A diet based on sunflower cake for lambs was assayed in order to reuse biodiesel industrial by-products with the aim of reducing livestock costs and evaluating their influence on meat quality. To achieve these goals, sixteen male lambs were fed diets containing different levels of sunflower cake (control, 5%, 10% and 15%). Afterwards, their semimembranosus muscles were analysed by two-dimensional electrophoresis coupled to mass spectrometry and their functional protein association was examined using STRING. Structural and metabolic proteins in the lambs’ proteomes changed significantly according to their diet. Fifteen proteins showed significant changes caused by the inclusion of sunflower cake, and the most differentially abundant structural proteins were detected in 2-DE gels from the lambs. Differentially abundant metabolic proteins such as ENO3 (enolase 3), MDH1 (malate dehydrogenase) and ALDH1A1 (retinal dehydrogenase) have been proposed as biomarkers of quality parameters in other species.  相似文献   
17.
18.
The consumption of brassica sprouts as raw vegetables provides a fair amount of glucosinolates (GLs) and active plant myrosinase, which enables the breakdown of GLs into health-promoting isothiocyanates (ITCs). This study reports the determination of the main constituents related to human health found in edible sprouts of two Brassica oleracea varieties, broccoli and Tuscan black kale, and two Raphanus sativus varieties, Daikon and Sango. Radish sprouts exhibited the highest ability to produce ITCs, with Daikon showing the greatest level of conversion of GLs into bioactive ITCs (96.5%), followed by Sango (90.0%). Tuscan black kale gave a value of 68.5%, whereas broccoli displayed the lowest with 18.7%. ITCs were not the exclusive GL breakdown products in the two B. oleracea varieties, since nitriles were also produced, thus accounting for the lower conversion observed. Measuring the release of plant ITCs is a valuable tool in predicting the potential level of exposure to these bioactive compounds after the consumption of raw brassica sprouts.  相似文献   
19.
The freeze-dried sprouts’ juice of Raphanus sativus (L.) cv. Sango was prepared and analysed for the first time. HPLC analysis of total isothiocyanates, after protein displacement, resulted in 77.8 ± 3.0 μmol/g of dry juice while GC–MS analysis of hexane and acetone extracts showed E- and Z-raphasatin (8.9 and 0.11 μmol/g, respectively) and sulforaphene (11.7 μmol/g), summing up to 20.7 ± 1.7 μmol/g of free isothiocyanates. Sprouts’ juice contained an unprecedented wealth of anthocyanins and a new fractionation methodology allowed us to isolate 34 mg/g of acylated anthocyanins (28.3 ± 1.9 μmol/g), belonging selectively to the cyanidin family. Analysis was performed by HPLC–PDA–ESI–MSn and extended to deacylated anthocyanins and aglycones, obtained, respectively, by alkaline and acid hydrolysis. This study identified 70 anthocyanins, 19 of which have never been described before and 32 of which are reported here in R. sativus for the first time. Sango radish sprouts are exceptional dietary sources of heath-promoting micronutrients.  相似文献   
20.
Consumption of Brassica vegetables containing glucosinolates is associated with decreased risk of cancer at several tissue sites. Studies of the relative potency and metabolism of the major dietary isothiocyanates have been hindered by limited availability of high‐purity isothiocyanates and their glucosinolate precursors. We describe a simple procedure for the preparation of glucosinolates sinigrin, gluconapin, progoitrin, glucoiberin, glucoraphanin, glucoalyssin and gluconasturtiin from vegetable seeds. Glucosinolates were extracted from the seeds of mustard, oilseed, broccoli, cauliflower and winter cress. Purification by preparative anion exchange and reversed‐phase column chromatography gave the pure glucosinolates. Good separation was achieved without using ion‐pair reagents. Related isothiocyanates and amine degradation products were prepared by myrosinase‐catalysed hydrolysis of the corresponding glucosinolate and by organic synthesis, respectively. The compounds were characterized by analytical HPLC, 1H NMR, 13C NMR, elemental analysis and mass spectrometry. Optimized conditions for detection and quantitation of these glucosinolates and metabolites by LC‐MS/MS are also given. Large‐scale glucosinolate preparation could be performed, giving amounts suitable for pharmacological evaluation in vivo. These methods will facilitate studies of the pharmacological activity and metabolism of dietary glucosinolates. Copyright © 2006 Society of Chemical Industry  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