全文获取类型
收费全文 | 10012篇 |
免费 | 1661篇 |
国内免费 | 323篇 |
专业分类
电工技术 | 554篇 |
技术理论 | 2篇 |
综合类 | 771篇 |
化学工业 | 203篇 |
金属工艺 | 35篇 |
机械仪表 | 153篇 |
建筑科学 | 7087篇 |
矿业工程 | 299篇 |
能源动力 | 56篇 |
轻工业 | 54篇 |
水利工程 | 787篇 |
石油天然气 | 89篇 |
武器工业 | 15篇 |
无线电 | 505篇 |
一般工业技术 | 244篇 |
冶金工业 | 82篇 |
原子能技术 | 11篇 |
自动化技术 | 1049篇 |
出版年
2024年 | 122篇 |
2023年 | 427篇 |
2022年 | 619篇 |
2021年 | 653篇 |
2020年 | 694篇 |
2019年 | 497篇 |
2018年 | 305篇 |
2017年 | 247篇 |
2016年 | 238篇 |
2015年 | 303篇 |
2014年 | 898篇 |
2013年 | 573篇 |
2012年 | 760篇 |
2011年 | 828篇 |
2010年 | 676篇 |
2009年 | 652篇 |
2008年 | 616篇 |
2007年 | 626篇 |
2006年 | 533篇 |
2005年 | 341篇 |
2004年 | 284篇 |
2003年 | 241篇 |
2002年 | 190篇 |
2001年 | 171篇 |
2000年 | 105篇 |
1999年 | 74篇 |
1998年 | 51篇 |
1997年 | 52篇 |
1996年 | 27篇 |
1995年 | 41篇 |
1994年 | 23篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1975年 | 1篇 |
1961年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
11.
Critical to restoring the nature conservation value of many river corridors is an understanding of how alluvial landscapes will respond to cessation of river management and land use practices that have previously degraded the environment. This paper analyses changes in valley floor landforms and vegetation patch dynamics, in relation to fluvial disturbance, over a period of almost 100 years following flood embankment abandonment on a wandering gravel‐bed river, namely the River Tummel, Scotland. Such rivers were once typical of many draining upland areas of northern maritime Europe. Prior to abandonment the valley floor landscape was agriculturally dominated and the river for the most part was single thread confined between flood embankments. The pattern of landform change and vegetation patch development over time following a decision in 1903 not to maintain embankments was tracked by geomorphic and land cover mapping utilizing successive sets of aerial photography for the period 1946 to 1994. A historical context for these changes was also feasible because the channel planform in 1900 and earlier channel planform changes dating back to 1753 were known due to the availability of old maps and earlier geomorphic studies. The land cover mapping was validated by comparison of results produced from the interpretation work on the 1994 aerial photographs with the field‐based UK National Vegetation Classification protocol. The findings of the study illustrate that bordering the River Tummel fluvial landforms and vegetation patch mosaics, presumably resembling those that occurred before valley floor land use intensification, evolved in less than 50 years after flood embankment abandonment with a resultant increase in habitat diversity. The change relates primarily to flood‐induced channel planform change and moderate levels of fluvial disturbance. The general significance of this change to plant species diversity on the valley floor of the River Tummel and elsewhere is discussed as is possible implications of the upstream impoundment and scenarios for climatically induced changes in flood frequency and magnitude. The overall outcome is the strong possibility that simple changes in river management and land use practices could result in re‐establishment of the nature conservation value of similar river corridors in Europe over the medium term without active restoration efforts. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
12.
The restoration of the red colour of carthamine (photo-bleached in polymeric heterosaccharide gels) was investigated using sodium salts, potassium salts, and alkali. Ca-alginate gel was stained with carthamine, and the red-dish membranes were exposed to fluorescent light for 2·5, 4·0 and 20 h (at 28°C). The resulting orange-yellow gel membranes were treated with Na- or K-citrate solution and the restoration of the red colouration was followed spectrophoto-metrically. The results indicate that the red colour of carthamine can be retained within the gel membranes, while yellow-coloured compounds were removed and/or transformed by the alkaline salt solutions. 相似文献
13.
北京某学校雨水利用设计 总被引:3,自引:0,他引:3
以北京市某中学为例,介绍一种学校雨水利用的方法。根据校区水量平衡计算结果,对利用校园内汇集的雨水作为冲厕、绿化和景观用水等进行设计;采取相应的技术措施,对雨水径流的污染进行控制,保障所利用雨水的水质达到要求,并采用生态净化的方式,使学校景观水体循环起来。虽然雨水利用工程投资较高,但其社会和环境效益显著。 相似文献
14.
15.
浅析建筑小品与植物的关系 总被引:3,自引:0,他引:3
章新海 《安徽建筑工业学院学报》2006,14(4):60-61
着重介绍了园林植物与建筑小品的配置的方法。建筑小品与植物一起配置,不仅可以获得和谐优美的景观,而且还可突出单体达不到的功能效果。 相似文献
16.
Motion picture films are susceptible to local degradations such as dust spots. Other deteriorations are global such as intensity
and spatial jitter. It is obvious that motion needs to be compensated for before the detection/correction of such local and
dynamic defects. Therefore, we propose a hierarchical motion estimation method ideally suited for high resolution film sequences.
This recursive block-based motion estimator relies on an adaptive search strategy and Radon projections to improve processing
speed. The localization of dust particles then becomes straightforward. Thus, it is achieved by simple inter-frame differences
between the current image and motion compensated successive and preceding frames. However, the detection of spatial and intensity
jitter requires a specific process taking advantage of the high temporal correlation in the image sequence. In this paper,
we present our motion compensation-based algorithms for removing dust spots, spatial and intensity jitter in degraded motion
pictures. Experimental results are presented showing the usefulness of our motion estimator for film restoration at reasonable
computational costs.
Received: 9 July 2000 / Accepted: 13 January 2002
Correspondence to:S. Boukir 相似文献
17.
Elena Crespi Antonio Capolongo Davide Fissore Antonello A. Barresi 《Drying Technology》2008,26(3):349-356
The aim of this article is to develop an experiment and a procedure to investigate the restoration of water-damaged paper and archival materials using freeze drying in order to allow a reproducible test and comparison of the influence of different operating conditions on drying time and restored paper quality. Firstly, a reproducible method for the preparation of soaked samples simulating water-damaged paper has been developed. Then, the samples have been freeze-dried in a laboratory-scale apparatus that allowed monitoring the temperature as well as the weight of the samples. The technique of evaporative freezing, which reduces the drying time required, has been used in this case. An innovative procedure for the visualization of the progress of the drying process has been validated, thus allowing the validation of a simple phenomenological model of the time evolution of the ice core volume; in addition, data on the residual moisture of the dried paper sheets in different zones have been given. Finally, optimization of this particular drying process by using simple or more sophisticated approaches has been discussed. 相似文献
18.
19.
游强盛 《有色冶金设计与研究》2004,25(4):40-44
通过南昌市某快速路的设计实例,认识到搞好快速路沿线各交叉口的方案设计是快速路规划设计的关键内容。道路交叉口设计应注重交通功能分析,满足路口交通需求,同时也不能忽视立交的景观要求。 相似文献
20.
用环境水利理念和方法建设富锦市城市防洪工程 总被引:2,自引:0,他引:2
本文结合富锦市城区堤防建设论述了城市防洪建设应从单一防洪目标逐步过渡到区域性多目标治理。以水利工 程为载体,推动促进环境的改善,实现防洪、水资源、生态环境以及城市景观建设的协调统一。 相似文献