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   2889篇
  免费   216篇
  国内免费   2篇
电工技术   20篇
综合类   1篇
化学工业   994篇
金属工艺   49篇
机械仪表   76篇
建筑科学   94篇
矿业工程   5篇
能源动力   103篇
轻工业   589篇
水利工程   19篇
石油天然气   18篇
无线电   188篇
一般工业技术   396篇
冶金工业   210篇
原子能技术   9篇
自动化技术   336篇
  2024年   8篇
  2023年   39篇
  2022年   220篇
  2021年   242篇
  2020年   106篇
  2019年   115篇
  2018年   116篇
  2017年   114篇
  2016年   122篇
  2015年   94篇
  2014年   139篇
  2013年   206篇
  2012年   177篇
  2011年   221篇
  2010年   136篇
  2009年   125篇
  2008年   111篇
  2007年   97篇
  2006年   96篇
  2005年   70篇
  2004年   61篇
  2003年   59篇
  2002年   53篇
  2001年   37篇
  2000年   39篇
  1999年   24篇
  1998年   57篇
  1997年   44篇
  1996年   33篇
  1995年   24篇
  1994年   20篇
  1993年   20篇
  1992年   10篇
  1991年   7篇
  1990年   9篇
  1989年   7篇
  1988年   7篇
  1987年   1篇
  1986年   7篇
  1985年   7篇
  1984年   3篇
  1983年   6篇
  1982年   6篇
  1980年   1篇
  1979年   2篇
  1978年   4篇
  1977年   1篇
  1976年   3篇
  1975年   1篇
排序方式: 共有3107条查询结果,搜索用时 15 毫秒
121.
The probiotic strains Lactobacillus brevis CCMA1284 and Lactobacillus plantarum CCMA0359 were microencapsulated by spray drying using different matrices – whey powder (W), whey powder with inulin (WI) and whey powder with maltodextrin (WM). Viability of the microencapsulated strains in acid and bile juices and during 90 days of storage (seven and 25 °C) was evaluated. The two strains exhibited high encapsulation efficiency (> 86%) by spray drying. The different matrices maintained L. plantarum viability above six log CFU g−1 at 7 °C for 90 days, whereas similar results for L. brevis were observed only for W. The use of inulin as matrix of encapsulation did not enhance bacterial viability in the evaluated conditions. In general, the use of W and WM as matrices was effective for L. plantarum viability. However, only W was effective for L. brevis in the evaluated conditions. The spray drying technique was successfully adopted for the encapsulation of L. plantarum CCMA0359 and L. brevis CCMA1284 strains.  相似文献   
122.
123.
Nowadays discourse parsing is a very prominent research topic. However, there is not a discourse parser for Spanish texts. The first stage in order to develop this tool is discourse segmentation. In this work, we present DiSeg, the first discourse segmenter for Spanish, which uses the framework of Rhetorical Structure Theory and is based on lexical and syntactic rules. We describe the system and we evaluate its performance against a gold standard corpus, divided in a medical and a terminological subcorpus. We obtain promising results, which means that discourse segmentation is possible using shallow parsing.  相似文献   
124.
The aim of this study was to develop fruit powders (apple, banana and strawberry) enriched with a probiotic strain (Lactobacillus plantarum 299v). Two methodologies were proposed: (i) drying of the fruit with probiotic culture incorporated (by convection) or (ii) drying of fruit (by convection) and addition of spray‐dried probiotic culture. In the first methodology, processing caused a notable reduction in probiotic viable counts in apple, but this reduction was lower during drying of banana and strawberry. A large reduction in viable cells was also recorded during storage. In the second methodology, the survival of L. plantarum 299v was considerably higher during spray‐drying, and fruit powders with a microbial content suitable for a probiotic food (108–10cfu g?1) were obtained. The fruit powders incorporating L. plantarum 299v can be stored at 4 °C or at room temperature, for at least 3 months. This preliminary study demonstrated that fruit powders are good carriers of probiotic cultures, but the techniques used to produce them should be carefully considered.  相似文献   
125.
Landsat 8 is the first Earth observation satellite with sufficient radiometric and spatial resolution to allow global mapping of lake CDOM and DOC (coloured dissolved organic matter and dissolved organic carbon, respectively) content. Landsat 8 is a multispectral sensor however, the number of potentially usable band ratios, or more sophisticated indices, is limited. In order to test the suitability of the ratio most commonly used in lake carbon content mapping, the green–red band ratio, we carried out fieldwork in Estonian and Brazilian lakes. Several atmospheric correction methods were also tested in order to use image data where the image-to-image variability due to illumination conditions would be minimal. None of the four atmospheric correction methods tested, produced reflectance spectra that matched well with in situ measured reflectance. Nevertheless, the green–red band ratio calculated from the reflectance data was in correlation with measured CDOM values. In situ data show that there is a strong correlation between CDOM and DOC concentrations in Estonian and Brazilian lakes. Thus, mapping the global CDOM and DOC content from Landsat 8 is plausible but more data from different parts of the world are needed before decisions can be made about the accuracy of such global estimation.  相似文献   
126.
A set of hydrodynamic methods in extremely dilute solutions (determination of intrinsic viscosity [η ], translational diffusion D and flotation in a centrifugal field s ) was used in the studies of conformational properties, dimensions and equilibrium rigidity of individual molecules of a series of samples of poly(3‐hexylthiophene). Absolute molecular masses M sD were determined. The Mark–Kuhn–Houwink equations for the range of M sD from 2240 to 15 300 g mol?1 are given. For the first time, an analysis of conformational properties and equilibrium flexibility of poly(3‐hexylthiophene) molecules was carried out using the model of a statistical segment containing a twisted polymer chain. © 2017 Society of Chemical Industry  相似文献   
127.
Lethal and teratogenic potentials of carbon nanoparticles (CNPs) in their amorphous form were investigated by the standardized Frog Embryo Teratogenesis Assay-Xenopus (FETAX), a 96-h in vitro whole-embryo toxicity test based on the amphibian Xenopus laevis. Embryos were acutely exposed to 1, 10, 100 and 500 mg/L CNP suspensions and evaluated for lethality, malformations and growth inhibition. Larvae were processed for histological and ultrastructural analyses to detect the main affected organs, to look for specific lesions at the subcellular level and to image and track CNPs into tissues. Only the highest CNP suspension resulted in being embryolethal for X. laevis larvae, while malformed larva percentages significantly differed from controls starting from 100 mg/L. The stomach and gut were the preferential CNP accumulation sites, on the contrary, the digestive epithelium remained intact. The analyses showed the presence of isolated nanoparticles and/or aggregates in different secondary target organs. CNPs were found in circulating erythrocytes. The research confirms the good tolerance of X. laevis towards pure elemental carbon in its nanoparticulate amorphous form, but highlights the possibility of CNP transfer toward all body areas.  相似文献   
128.
Synthetic methods have been developed to prepare oxazaborines, the azaanalogues of 2,2-difluoro-1,3,2(2H)dioxaborines, which can form merocyanine dyes. The first oxazaborine merocyanines with the isomeric position of the coordinating nitrogen atom have also been obtained. Comparing the spectral properties of donor-acceptor dioxa- and oxazaborine dyes, it is seen that substitution of the 3-O atom by the NH group in the chelate ring has a slight effect on absorption and fluorescence band positions but causes the intensity redistribution between the 0-0 and 0-1 vibronic absorption peaks and thus induces a change in the absorption band shape due to the enhanced solvation of oxazaborines. Substitution of the 1-O ring atom by the NPh group leads to a bathochromic shift and a manifold increase in the fluorescence quantum yield for the corresponding boron chelate dyes.  相似文献   
129.
Multimedia Tools and Applications - We present an analysis of how visually impaired people perform gestures on touch-screen smartphones and report their preferences, explaining the procedure and...  相似文献   
130.
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