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   785篇
  免费   53篇
  国内免费   1篇
电工技术   6篇
化学工业   237篇
金属工艺   8篇
机械仪表   9篇
建筑科学   20篇
矿业工程   5篇
能源动力   10篇
轻工业   175篇
水利工程   6篇
石油天然气   6篇
无线电   75篇
一般工业技术   71篇
冶金工业   121篇
自动化技术   90篇
  2023年   3篇
  2022年   34篇
  2021年   29篇
  2020年   15篇
  2019年   17篇
  2018年   23篇
  2017年   22篇
  2016年   22篇
  2015年   23篇
  2014年   24篇
  2013年   55篇
  2012年   44篇
  2011年   43篇
  2010年   38篇
  2009年   38篇
  2008年   39篇
  2007年   43篇
  2006年   19篇
  2005年   20篇
  2004年   26篇
  2003年   21篇
  2002年   22篇
  2001年   15篇
  2000年   7篇
  1999年   9篇
  1998年   19篇
  1997年   14篇
  1996年   9篇
  1995年   13篇
  1994年   6篇
  1993年   12篇
  1992年   7篇
  1991年   8篇
  1990年   6篇
  1989年   7篇
  1988年   4篇
  1987年   12篇
  1986年   3篇
  1985年   5篇
  1984年   5篇
  1983年   6篇
  1982年   4篇
  1981年   4篇
  1980年   3篇
  1979年   4篇
  1978年   7篇
  1976年   7篇
  1975年   4篇
  1973年   3篇
  1969年   2篇
排序方式: 共有839条查询结果,搜索用时 15 毫秒
1.
The recent introduction of the Asian yellow-legged hornet, Vespa velutina, into Europe has raised concern regarding the threat to honeybees and the competition with the European hornet, Vespa crabro. The aim of this study was to investigated essential (Mg, Fe, Zn, Cu) and non-essential (Cd and Pb) elements in these two species. Element concentrations were determined in the whole body and separately in the head, thorax and abdomen using atomic absorption spectrometry (AAS). The changes in essential element concentration and speciation during metamorphosis were also studied using size exclusion chromatography followed by AAS and proteomic analysis. In both species, the essential elements were more concentrated in the abdomen due to the presence of fat bodies. Magnesium, Fe and Zn concentrations were significantly higher in V. crabro than in V. velutina and could have been related to the higher aerobic energy demand of the former species required to sustain foraging flight. Low concentrations of Cd and Pb were indicative of low environmental exposure. The concentration and speciation of essential elements, particularly Fe, varied among the developmental stages, indicating a modification of ligand preferences during metamorphosis. Overall, the results in the present study provide a better understanding of the hornet metal metabolism and a foundation for additional studies.  相似文献   
2.
We report the results of the first national survey of psychologists in private practice regarding their participation in peer consultation groups. The sample (71% return) was drawn from 800 randomly selected psychologists listed in the National Register of Health Service Providers in Psychology. We found that 23% of the sample currently belonged to peer consultation groups, and 24% had belonged in the past. Of those not currently in groups, 61% expressed the desire to belong if one were available. There were virtually no significant demographic differences between current members and nonmembers. We examined the following group characteristics: formation, length of existence, size, membership, leadership, theoretical orientation, range of experience, time and place, content, and group process. Groups tended to be small, informal, and leaderless; however, we found great variation among groups on all dimensions. Findings also showed a high degree of satisfaction with membership. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
3.
Summary From model roastings of mixtures containing serine, threonine and sucrose about 350 volatile compounds were separated and identified by GC/MS. Among them there were more than 100 monocyclic furans, 13 furanones and 8 bicyclic furans, the mass spectra and retention indices of which are recorded. The most important mass spectrometric fragmentation pathways are described. Spectra obtained from roasting coffee under identical conditions are compared with the spectra from model roastings.
Modell-Reaktionen zur Röstaroma-BildungII. Die massenspektrometrische Identifizierung von Furanen und Furanonen aus der Reaktion von Serin und Threonin mit Saccharose unter den Bedingungen der Kaffeeröstung
Zusammenfassung Aus Modellröstungen von Gemischen aus Serin, Threonin und Saccharose unter den Bedingungen der Kaffeeröstung wurden etwa 350 flüchtige Verbindungen mittels GC/MS getrennt und identifiziert. Unter ihnen befanden sich über 100 monocyclische Furane und 13 Furanone sowie 8 bicyclische Furane, deren Massenspektren und Retentions-indices angegeben werden. Die wichtigsten massenspektrometrischen Fragmentierungswege werden beschrieben. -Die aus einer gleich behandelten Röstung von Rohkaffee erhaltenen Spektren werden mit denen der Modellröstungen verglichen.


Dissertation Gloria Bochmann, TU Berlin 1984  相似文献   
4.
BACKGROUND: The first stage of the cork industrial process generates great volumes of wastewater with moderate to high organic pollutant content that must be purified using different procedures, such as filtration by membranes. RESULTS: The tangential filtration of these wastewaters was studied using two different laboratory equipments. In the first one, three ultrafiltration (UF) membranes were tested, with molecular weight cut‐off (MWCO) 100 kDa and 30 kDa, and two operating modes were used: total recycling of permeate and retentate streams, and in continuous mode, without recycling both streams. In the total recycling UF experiments, the influence of the operating variables on the permeate flux was first established. The effectiveness of the different membranes was determined by evaluating the rejection coefficients for several parameters that measure the global pollutant content of the effluent. The values found for these rejection coefficients were in the following order: ellagic acid and color > absorbance at 254 nm > tannic content > COD (chemical oxygen demand). In the continuous mode experiments, the fouling mechanism for each membrane was established by fitting the experimental data to various filtration fouling models given in the literature. The operating mode in the second equipment was batch concentration, and additional experiments were carried out with an UF membrane (2 kDa), and with a NF membrane (with MWCO in the range 150–300 Da). CONCLUSIONS: The three operating modes tested provided different rejection levels of organic matter; among them, the most effective procedure tested was batch concentration mode using a NF membrane. Copyright © 2007 Society of Chemical Industry  相似文献   
5.
We present a tool that starting from high-level specifications of switched-capacitor (SC) /spl Sigma//spl Delta/ modulators calculates optimum specifications for their building blocks and then optimum sizes for the block schematics. At both design levels, optimization is performed using statistical techniques to enable global design and innovative heuristics for increased computer efficiency as compared with conventional statistical optimization. The tool uses an equation-based approach at the modulator level, a simulation-based approach at the cell level, and incorporates an advanced /spl Sigma//spl Delta/ behavioral simulator for monitoring and design space exploration. We include measurements taken from two silicon prototypes: (1) a 16 b @ 16 kHz output rate second-order /spl Sigma//spl Delta/ modulator; and (2) a 17 b @ 40 kHz output rate fourth-order /spl Sigma//spl Delta/ modulator. Both use SC fully differential circuits and were designed using the proposed tool and manufactured in a 1.2 /spl mu/m CMOS double-metal double-poly technology.<>  相似文献   
6.
The WAIS-R Information subtest was combined with 21 potential substitute Canadian content items and group-administered to 119 high school students ranging in age from 16 to 19 years. Seven acceptable substitute items were identified. Mean scores on the American items for the 16-17 and 18-19 age groups suggested that Canadians of these ages are not penalized by American content with respect to either Verbal or Full Scale IQ. Nevertheless, the research identified eight Information items, four easier and four more difficult than the standard WAIS-R implies. Similar results were noted in two previous studies of the WAIS-R, and indicate the extreme caution required for the clinical interpretation of intra test scatter. There is also evidence that item difficulty within the Information subtest may vary with the age of the subject. These results were considered indicative of the necessity for Canadian content Information items and the development of Canadian norms for an adapted WAIS-R Information subtest. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
7.
Reviews the book, Basic Processes in Reading Visual Word Recognition by Derek Besner and Glyn W. Humphreys (see record 1990-99017-000). While there has been an increase in the amount of work on many different aspects of reading, as Besner and Humphreys point out in the overview to their book, the vast majority of the research on the topic of reading in the past twenty years has been concerned with the processes involved in word recognition. For this reason, Besner and Humphreys have attempted to bring together studies on topics which are both relevant to current debates in the field of word recognition, and which are likely to be important for future developments in the field. They have compiled an edited volume consisting of their overview and eight additional chapters. The editors have attempted to span the continuum of processes involved in word recognition and thus have included chapters which cover topics ranging from the visual analysis of words, to those on the influence of semantic factors on word recognition. The authors of these chapters comprise an impressive list of researchers in the field of word recognition, with the majority of chapters being authored by leading researchers on the topic. Given the stature of the authors and the range of topics covered, in theory this volume should provide a very thorough overview of current theory and research on reading. There is no question that each of the chapters is interesting and important in its own right. However, in practice the volume as a whole fell somewhat short of my expectations. The different tacts taken by different authors has resulted in a very uneven coverage of the current debates in the field. Notwithstanding these criticisms, I am sure that the majority of researchers in this field will consider this volume to be an important contribution. The book would provide a very useful addition to graduate courses in cognitive sciences and as a supplemental text for an undergraduate course on the psychology of reading. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
8.
To make exploring a locale's heritage a challenging and compelling experience, the Venice Game uses a handheld platform and educational software that leverages video game techniques.  相似文献   
9.
The decision on technologies used for reclaiming wastewater appears as important as a consequence of the implications on the economic, environmental and health conditions of societies. The problem arises when deciding how to deal with wastewater in small communities, because the costs of implementing and operating small, intensive wastewater treatment plants are unacceptable and can lead to financing and operation problems. Extensive treatment systems can be a good solution, where space is available. This paper presents the combination of two soft technologies (infiltration-percolation and constructed wetlands) to treat and reclaim wastewater. The obtained results show that the infiltration-percolation effluent presents a quality enough to be reused for irrigation of industrial crops, nurseries, fodder, cereals and oleaginous seeds, ornamental flower production; industrial cooling; impoundments, water bodies, and streams for recreational use in which the public's contact with the water is not permitted; and irrigation of forested areas, landscape areas and restricted access areas. Moreover, the combination of infiltration-percolation and constructed wetlands increases the list of final reclamation to the following: irrigation of pasture for milk or meat animals, crops for canning industry, crops not raw-consumed, fruit trees except by sprinkling, aquaculture; and aquifer recharge by localised percolation through the soil.  相似文献   
10.
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