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   3228篇
  免费   195篇
  国内免费   4篇
电工技术   64篇
综合类   1篇
化学工业   864篇
金属工艺   43篇
机械仪表   73篇
建筑科学   152篇
矿业工程   1篇
能源动力   101篇
轻工业   244篇
水利工程   10篇
石油天然气   3篇
武器工业   1篇
无线电   297篇
一般工业技术   585篇
冶金工业   137篇
原子能技术   28篇
自动化技术   823篇
  2024年   5篇
  2023年   41篇
  2022年   132篇
  2021年   150篇
  2020年   76篇
  2019年   89篇
  2018年   99篇
  2017年   92篇
  2016年   144篇
  2015年   113篇
  2014年   147篇
  2013年   221篇
  2012年   202篇
  2011年   230篇
  2010年   194篇
  2009年   192篇
  2008年   179篇
  2007年   167篇
  2006年   120篇
  2005年   96篇
  2004年   118篇
  2003年   98篇
  2002年   64篇
  2001年   52篇
  2000年   43篇
  1999年   35篇
  1998年   28篇
  1997年   25篇
  1996年   35篇
  1995年   27篇
  1994年   26篇
  1993年   20篇
  1992年   21篇
  1991年   10篇
  1990年   7篇
  1989年   11篇
  1988年   5篇
  1987年   14篇
  1986年   7篇
  1985年   16篇
  1984年   17篇
  1983年   11篇
  1982年   8篇
  1981年   7篇
  1980年   4篇
  1979年   6篇
  1978年   4篇
  1977年   6篇
  1975年   3篇
  1973年   3篇
排序方式: 共有3427条查询结果,搜索用时 15 毫秒
191.
192.
The work described here deals with the effectiveness of using high-pressure carbon dioxide treatment (HPCD) to stabilise freshly squeezed blood orange juice. Technical planning of a continuous high-pressure supercritical carbon dioxide pilot system, suitable for development on an industrial scale, was carried out in our lab. To determine the optimal operating conditions (temperature, pressure, and CO2/juice ratio), three different experimental trials were carried out. The first trial was conducted at 230 bar, 36 ± 1 °C, 5.08 L/h juice flow rate, and 3.91 L/h CO2 flow rate, corresponding to a gCO2/gjuice ratio of 0.770. The second trial utilised the same conditions except that the operative pressure was reduced (130 bar). The third trial was carried out at 130 bar, 36 ± 1 °C, 5.08 L/h juice flow rate, 1.96 L/h CO2 flow rate, corresponding to a 0.385 gCO2/gjuice ratio. The effects of processing were evaluated by determining physicochemical, antioxidant, and microbiological parameters of the treated juices. In addition, once the best operative parameters had been determined, physicochemical, antioxidant, microbiological and sensory evaluation of fresh blood orange juice stabilised by HPCD treatment was carried out during refrigerated storage of juices at 4 ± 1 °C for thirty days. The results showed that HPCD treatment cannot be considered as an alternative to traditional thermal methods but as a new mild technology for producing a stabilised blood orange juice with a shelf-life of 20 days.Industrial relevanceBlood oranges are the main cultivated varieties of Citrus sinensis (L.) Osbeck in Italy. Freshly squeezed blood orange juice exert a high antiradical and antioxidant activity, due to its rich phenolic profile, but its preservation is usually assured by thermal treatment which affects its nutritional and sensory value. In this study we proposed a “milder” continuous HPCD process suitable for implementation on an industrial scale. The HPCD stabilised juice retains its physicochemical, antioxidant, and sensory properties and could be placed within a new retail framework, namely, that of fresh juices with a shelf-life of 20 days.  相似文献   
193.
194.
This work was undertaken to study the serotypes and pulsotypes of 674 Listeria monocytogenes isolates from human (57), food (558) and environmental (59) sources, collected from different Italian geographical areas during 2002–2005, to determine whether certain subtypes were associated with certain foods and more often involved in cases of listeriosis, and to determine possible geographical or temporal associations. Eleven different L. monocytogenes serotypes were found in the food, environmental and human isolates. Most isolates belonged to only four serotypes (1/2a, 1/2b, 1/2c, 4b). The isolates were divided into 133 distinct AscI pulsotypes grouped into 26 pulsogroups. Pulsogroups ranged from a minimum of 2 up to 212 isolates, and contained 1–19 different pulsotypes. When associations between subtypes and isolates from specific foods selected as being most frequently involved in cases of listeriosis were tested some of these associations were highly significant but not exclusive, indicating that there was no close correlation between specific subtypes and specific food products. Despite the limitations of this study (few human isolates versus many food isolates prevalently collected from one food category), we believe that a large-scale database of L. monocytogenes subtypes and a timely epidemiological investigation can facilitate risk assessment and outbreak detection and control.  相似文献   
195.
Browsing large image collections is a complex and often tedious task, due to the semantic gap existing between the user subjective notion of similarity and the one according to which a browsing system organizes the images. In this paper we propose PIBE, an adaptive image browsing system, which provides users with a hierarchical view of images (the Browsing Tree) that can be customized according to user preferences. A key feature of PIBE is that it maintains local similarity criteria for each portion of the Browsing Tree. This makes it possible both to avoid costly global reorganization upon execution of user actions and, combined with a persistent storage of the Browsing Tree, to efficiently support multiple browsing tasks. We present the basic principles of PIBE and report experimental results showing the effectiveness of its browsing and personalization functionalities.  相似文献   
196.
体育就是展现   总被引:1,自引:0,他引:1  
水润宇 《建筑创作》2006,(7):156-167
如果我们要寻找体育建筑的基本元素,可能要承认广泛参与的理念是其最具启迪意义的。体育不是(或不再是)体能形式的神圣展示,而纯粹是能力与竞争精神的表达。不幸的是体育也成为被“造星体制”腐蚀的领域,作为一项大型的商业活动,体育原本纯洁的精神被掩盖和破坏。  相似文献   
197.
A new algorithm for the retrieval of columnar water vapor content is presented. The proposed procedure computes the area of the H2O absorption centered about 940 nm to allow its integrated columnar abundance as well as its density at ground level to be assessed. The procedure utilizes the HITRAN 2000 database as the source of H2O cross-section spectra. Experimental results were derived from radiometrically calibrated hyperspectral images collected by the Airborne Visible-Infrared Imaging Spectrometer (AVIRIS) sensor over the Cuprite mining district in Nevada. Numerical simulations based on the MODTRAN 4 radiative transfer code were also employed for investigating the algorithm's performance. An additional empirical H2O retrieval procedure was tested by use of data gathered by the VIRS-200 imaging spectrometer.  相似文献   
198.
The energy and economy scenarios between the end of World War II and the oil crisis of 1973 are critically evaluated. The profound changes produced by the oil crisis of 1973–1974 are noted. An examination is then made, in a historical and economic context, of the energy policies of the Western industrialized countries after 1973. This assessment examines not only the potentials of these policies in satisfying short-to medium-term energy requirements, but also their impact on the basic, longer-term development problems of industrialized and developing countries.  相似文献   
199.
In this paper, four characterizations of stabilizability and detectability of linear periodic systems are considered. Two of them look as natural extensions of the classical definitions given for time-invariant systems. The remaining two are modal characterizations which turn out to be useful in the analysis of the periodic Lyapunov and Riccati equations. It is shown that all these notions of stabilizability (and detectability) are in fact equivalent to each other.One of the various definitions calls for the existence of the Kalman canonical decomposition of periodic systems. This issue is addressed in the Appendix.  相似文献   
200.
This paper describes an approach to the acquisition and representation of information on 3D painted surfaces (usually frescoes) based on the tassellation and mosaicing of the whole surface. The acquisition is carried out using an active vision system specifically designed for these purposes. In this paper, particular emphasis is placed on the mosaicing procedure of the acquired images, which, while conceptually simple, allows one to obtain very good results thanks to the effective exploitation of the features of the acquisition system. A careful qualitative and quantitative analysis of the performances of the system, obtained through tests on real scenes in the laboratory, is also presented.Received: 28 May 2001, Accepted: 8 November 2002, Published online: 18 June 2003 Correspondence to: Paolo GrattoniMassimiliano Spertino: With I.R.I.T.I. under grant N.202.12484 of the Italian Safeguard of Cultural Heritage C.N.R. project.  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