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   573篇
  免费   22篇
电工技术   3篇
化学工业   265篇
金属工艺   7篇
机械仪表   18篇
建筑科学   11篇
矿业工程   1篇
能源动力   14篇
轻工业   110篇
石油天然气   1篇
无线电   10篇
一般工业技术   81篇
冶金工业   18篇
原子能技术   1篇
自动化技术   55篇
  2023年   10篇
  2022年   58篇
  2021年   59篇
  2020年   18篇
  2019年   18篇
  2018年   13篇
  2017年   16篇
  2016年   18篇
  2015年   16篇
  2014年   18篇
  2013年   42篇
  2012年   33篇
  2011年   41篇
  2010年   36篇
  2009年   32篇
  2008年   42篇
  2007年   21篇
  2006年   17篇
  2005年   17篇
  2004年   12篇
  2003年   3篇
  2002年   6篇
  2001年   7篇
  2000年   8篇
  1999年   5篇
  1998年   4篇
  1997年   1篇
  1996年   3篇
  1995年   4篇
  1994年   4篇
  1992年   3篇
  1990年   5篇
  1989年   1篇
  1985年   2篇
  1984年   1篇
  1983年   1篇
排序方式: 共有595条查询结果,搜索用时 0 毫秒
81.
The aim was to study the effects of Debaryomyces hansenii and Yarrowia lipolytica strains, used with lactic acid starter cultures (Lactobacillus plantarum), in the manufacture of dried fermented sausages in order to understand their effects on volatile profile, biogenic amine content and sensory properties. The experimental data showed that every yeast strain produced a specific profile of volatile metabolic products. The yeasts also gave sausages with distinctive sensory properties. The degree of mincing also influenced these properties, but none of these factors had significant influence upon the accumulation of biogenic amines.  相似文献   
82.
The development of a solution‐deposited up‐converted distributed feedback laser prototype is presented. It employs a sol–gel silica/germania soft‐lithographed microcavity and CdSe–CdZnS–ZnS quantum dot/sol–gel zirconia composites as optical gain material. Characterization of the linear and nonlinear optical properties of quantum dots establishes their high absorption cross‐sections in the one‐ and two‐ photon absorption regimes to be 1 × 10?14 cm2 and 5 × 104 GM, respectively. In addition, ultrafast transient absorption dynamics measurements of the graded seal quantum dots reveal that the Auger recombination lifetime is 220 ps, a value two times higher than that of the corresponding CdSe core. These factors enable the use of such quantum dots as optically pumped gain media, operating in the one‐ and two‐photon absorption regime. The incorporation of CdSe–CdZnS–ZnS quantum dots within a zirconia host matrix affords a quantum‐dot ink that can be directly deposited on our soft‐lithographed distributed feedback grating to form an all‐solution‐processed microcavity laser.  相似文献   
83.
Human milk is frequently heat‐treated in hospitals, particularly milk that is banked, to destroy contaminating bacteria and viruses, but this treatment simultaneously reduces the content of some vitamins, enzymes, and immunological and nutritional factors. This study was performed to find the optimal conditions for heat treatment. The effects of 2 pasteurization temperatures on levels of protein sulfur amino acids (methionine, cystine) and some free amino acids (taurine, glutamine, glutamic acid) in light of the oxidative instability that occurs especially during thermal treatment were examined. These substances in raw human milk and in milk treated at 56.5 °C and 62.5 °C for 30 min were compared. Samples of mature human milk from all feeds over 24 h were obtained from 13 healthy well‐nourished mothers of term infants. Each sample was divided into 3 parts: raw, treated at 56.5 °C for 30 min, treated at 62.5 °C for 30 min. The results showed that the availability of sulfur amino acids and free taurine is the same after heat treatment, whereas milk processing increased positively the levels of free glutamic acid and glutamine, but there is significance only for glutamine. The mean quantities of considered amino acids were similar in milk treated at the recommended pasteurization temperature (30 min at 62.5 °C) and at 56.5 ° for 30 min.  相似文献   
84.
By means of an apparatus featuring a set of suspended baited containers, search abilities of 4 capuchin monkeys (Cebus apella) were evaluated. The experiment featured different spatial configurations of the search space. Results showed that monkeys exhaustively searched 9 containers spatially distributed as a 3?×?3 matrix, a cross, a line, or a circle. Search efficiency was higher when the search space featured either a linear or circular arrangement of containers. When faced with a linear arrangement of containers, the subjects developed principled search trajectories from 1 end to the other of the linear array. This behavioral regulation was independent from search efficiency as measured by the amount of visits to containers already explored. The data suggest that monkeys use either the travel distance or the cognitive costs associated with unprincipled travel trajectories as currency for regulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
85.
This review of the literature on varietal change in sub-Saharan Africa looks in detail at adoption of new varieties of bananas in Uganda, cassava in Nigeria, potato in Kenya, sweetpotato in Uganda and yams in Côte d’Ivoire. The review explored three hypotheses about drivers of varietal change. There was a strong confirmation for the hypothesis that insufficient priority given to consumer-preferred traits by breeding programmes contributes to the limited uptake of modern varieties (MVs) and low varietal turnover. Lack of evidence meant the second hypothesis of insufficient attention to understanding and responding to gender differences in consumer preferences for quality and post-harvest traits was unresolved. The evidence on the third hypothesis about the informal seed system contributing to slow uptake of MVs was mixed. In some cases, the informal system has contributed to rapid uptake of MVs, but often it appears to be a barrier with inconsistent varietal naming a major challenge.  相似文献   
86.
Foodborne disease caused by Salmonella represents a worldwide public health problem. In Europe, salmonellosis is still the second most commonly recorded zoonosis. Since the standard culture method for detecting Salmonella (ISO 6579:2002) requires up to 5 days to produce results, the need to develop rapid methods represents an important issue for the authorities and the producers. The aim of the present study was the in-house validation, according to ISO 16140, of an open-formula diagnostic real-time PCR for the detection of Salmonella in all the different meat categories reported in the EU Regulations relative to microbiological criteria for food safety. The assay employed specific primers and a probe target within the ttrRSBCA locus, which allows the tetrathionate respiration in Salmonella. Selectivity, relative accuracy, relative sensitivity and relative specificity were established by testing 110 bacterial strains and 175 various edible meat samples. Results showed 100 % selectivity, 100 % relative accuracy, 100 % relative sensitivity and 100 % relative specificity of the real-time PCR when compared to the standard culture method used as reference. In addition, in order to minimize the effect of the competitive micro-flora naturally present on meat samples, a highly nutritious and selective commercial medium (ONE Broth Salmonella, Oxoid) was evaluated in comparison with the classical non-selective pre-enrichment broth (buffered peptone water). Results demonstrated that the ONE Broth Salmonella medium increases the growth of Salmonella in the presence of competitive micro-flora.  相似文献   
87.
The Study and Production of Exotic Species (SPES) project employs a 100 MeV, 30 mA proton beam that strikes a primary target. The resulting high-energy neutron flux impinges on a secondary target of depleted uranium to produce, through fission, beams of short-lived, neutron-rich nuclei. This paper deals with some of the preliminary shielding calculations for the bunker. Monte Carlo is employed with MCNPX and, because of the deep penetrations involved, the in-house variance reduction optimiser, the direct statistical approach. The calculations exhibited a number of typical features that are addressed and discussed.  相似文献   
88.
Novel optically active methacrylic copolymers, bearing carbazole and azoaromatic moieties linked to the main chain with a rigid (S)-hydroxysuccinimide residue of one prevailing absolute configuration, have been prepared and characterized with the aim to establish the effects of the chiral group and of the dipolar interactions between the two side-chain chromophores on their properties.In particular, the observed chiroptical properties suggest the presence of ordered chiral conformations at least for chain segments of the macromolecules. Spectroscopic, thermal and chiroptical characterizations of these copolymers demonstrate the occurrence of significant electronic interactions between carbazole chromophores and azobenzene moieties. These interactions are related to the unusual partially alternating structure of the investigated copolymers and the relevant chiroptical and thermal properties. In fact, the polymeric derivates show high glass transition temperatures and good thermal stability, thus opening the way to a variety of potential applications based on photoconductive and optoelectronic properties.  相似文献   
89.
Cell migration is a crucial event for physiological processes, such as embryonic development and wound healing, as well as for pathological processes, such as cancer dissemination and metastasis formation. Cancer cell migration is a result of the concerted action of matrix metalloproteinases (MMPs), expressed by cancer cells to degrade the surrounding matrix, and integrins, the transmembrane receptors responsible for cell binding to matrix proteins. While it is known that cell-microenvironment interactions are essential for migration, the role of the physical state of such interactions remains still unclear. In this study we investigated human fibrosarcoma cell migration in two-dimensional (2D) and three-dimensional (3D) fibronectin (FN) microenvironments. By using antibody blocking approach and cell-binding site mutation, we determined that $\upalpha _{5}\upbeta _{1}$ -integrin is the main mediator of fibrosarcoma cell migration in 2D FN, whereas in 3D fibrillar FN, the binding of $\upalpha _{5}\upbeta _{1}$ - and $\upalpha _\mathrm{v}\upbeta _{3}$ -integrins is not necessary for cell movement in the fibrillar network. Furthermore, while the general inhibition of MMPs with GM6001 has no effect on cell migration in both 2D and 3D FN matrices, we observed opposing effect after targeted silencing of a membrane-bound MMP, namely MT1-MMP. In 2D fibronectin, silencing of MT1-MMP results in decreased migration speed and loss of directionality, whereas in 3D FN matrices, cell migration speed is increased and integrin-mediated signaling for actin dynamics is promoted. Our results suggest that the fibrillar nature of the matrix governs the migratory behavior of fibrosarcoma cells. Therefore, to hinder migration and dissemination of diseased cells, matrix molecules should be directly targeted, rather than specific subtypes of receptors at the cell membrane.  相似文献   
90.
One of the most important problems affecting geothermal fields is the abatement of hydrogen chloride contained in the vapor phase. If the chloride concentration exceeds a few ppmw, steam scrubbing must be provided in order to prevent corrosion of the gathering system and turbine failure. In some fields at Larderello, one of the most important geothermal areas in Italy, steam scrubbing is performed by injecting a caustic solution directly into the steam pipeline. In particular, the abatement system depends on absorption with chemical reaction of hydrogen chloride by a sodium hydroxide solution. This paper describes some of the Larderello power plant abatement systems and presents analyses of the different solutions adopted for this purpose. Finally, some simplified models for computing abatement efficiency in sprays, pipelines, static mixers, cyclones and vane type demisters—the equipment generally used in these plants—are proposed. The proposed models are able to predict the data measured in these power plants with good accuracy, and so they can be regarded as useful tools for designing new abatement systems or optimizing the existing ones.  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