全文获取类型
收费全文 | 5486篇 |
免费 | 119篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 56篇 |
综合类 | 2篇 |
化学工业 | 760篇 |
金属工艺 | 120篇 |
机械仪表 | 66篇 |
建筑科学 | 171篇 |
矿业工程 | 29篇 |
能源动力 | 52篇 |
轻工业 | 336篇 |
水利工程 | 22篇 |
石油天然气 | 9篇 |
无线电 | 297篇 |
一般工业技术 | 519篇 |
冶金工业 | 2775篇 |
原子能技术 | 39篇 |
自动化技术 | 354篇 |
出版年
2022年 | 32篇 |
2021年 | 46篇 |
2020年 | 50篇 |
2019年 | 44篇 |
2018年 | 60篇 |
2017年 | 42篇 |
2016年 | 69篇 |
2015年 | 58篇 |
2014年 | 79篇 |
2013年 | 88篇 |
2012年 | 115篇 |
2011年 | 136篇 |
2010年 | 115篇 |
2009年 | 109篇 |
2008年 | 116篇 |
2007年 | 112篇 |
2006年 | 103篇 |
2005年 | 127篇 |
2004年 | 80篇 |
2003年 | 79篇 |
2002年 | 82篇 |
2001年 | 88篇 |
2000年 | 82篇 |
1999年 | 134篇 |
1998年 | 838篇 |
1997年 | 493篇 |
1996年 | 341篇 |
1995年 | 222篇 |
1994年 | 186篇 |
1993年 | 195篇 |
1992年 | 67篇 |
1991年 | 80篇 |
1990年 | 72篇 |
1989年 | 75篇 |
1988年 | 61篇 |
1987年 | 56篇 |
1986年 | 52篇 |
1985年 | 67篇 |
1984年 | 30篇 |
1983年 | 32篇 |
1982年 | 45篇 |
1981年 | 45篇 |
1980年 | 40篇 |
1979年 | 52篇 |
1978年 | 25篇 |
1977年 | 80篇 |
1976年 | 180篇 |
1975年 | 26篇 |
1974年 | 18篇 |
1972年 | 18篇 |
排序方式: 共有5607条查询结果,搜索用时 15 毫秒
81.
Dorn R. Baumgartner A. Goth A. Gutu-Nelle A. Koppenborg J. Rehm W. Schneider R. Schneider S. von Wirth J. Weber D. 《Lightwave Technology, Journal of》1991,9(6):709-714
Mechanically shaped preforms (MSP) have been demonstrated to combine economic non-CVD (chemical vapor deposition) processing and low loss, with a published value of 0.63 dB/km and a size of 30 fkm/preform. Improved processing is proposed which results in a minimum loss of 0.27 dB/km at 1550 nm. Preforms capable of yielding 150 fkm have been produced. Reboiling during preform stretching and fiber pulling is identified as the last remaining problem of the process 相似文献
82.
83.
Ralph Schneider Wolfgang Marquardt 《Chemical engineering science》2002,57(10):1763-1792
Information technology has been becoming increasingly important in all areas of engineering during the last few years. Much of the progress achieved in chemical engineering would not have been possible without the enabling methods and tools provided by information technology. This trend will continue in the future but most likely with a considerably wider scope. While individual software tools and services have been in focus until recently, their integration into engineering work processes is an emerging and challenging area of research and development. This contribution attempts to highlight state of the art and future trends in supporting the activities during the life cycle of a chemical process by means of information technology. Emphasis will be largely on the process and plant design process rather than on procurement, manufacturing, and distribution of materials in the supply chain. 相似文献
84.
The common way to construct Voronoi tessellations is to compare the distances between given reference points using a given
distance function. To generalize this distance-function concept we expand an existing approach which defines distance functions
by their ``unit circles'. Our new approach allows modeling the ``unit circles' by a closed Spline curve. Changing the control
polygon directly affects the tessellation's appearance. Typically generalized Voronoi diagrams are represented by Voronoi
vertices and curves separating the individual tiles. To obtain interactive modeling we extended an existing hardware accelerated
rendering approach computing a bitmap-representation using different colors for individual tiles. With our extension, we are
able to use our Spline distance representations as input for a growing process. This growing process easily takes into account
weighting approaches like multiplicative, additive, and even free functional weighting. 相似文献
85.
86.
Decay of hollow atoms above and below a surface 总被引:1,自引:0,他引:1
87.
88.
FJ Martinez I Stanopoulos R Acero FS Becker R Pickering JF Beamis 《Canadian Metallurgical Quarterly》1994,105(1):168-174
The evaluation of dyspnea is problematic when a cause is inapparent after initial diagnostic studies. We examined the results and role of cardiopulmonary exercise testing (CPET) in 50 patients with a mean 23 months of dyspnea and normal FEV1 and FVC. The CPET studies were interpreted by a panel and a consensus reached. Subsequent tests ordered by the primary physician were reviewed, and a final diagnosis was agreed on by the panel. Seven of 50 patients had cardiac limitation, 17 of 50 had pulmonary limitation, 14 of 50 had obesity and/or deconditioning, 1 of 50 had gastroesophageal reflux, and 16 of 50 had either psychogenic dyspnea or no identifiable disease. Five patients had more than one clinical diagnosis accounting for 55 diagnoses in the 50 patients. Those with a normal CPET had a higher VO2max and O2 pulse than those with cardiac disease, deconditioning, or hyperactive airways disease (HAD) (p < 0.05). Electrocardiographic changes identified cardiac disease while studies demonstrating ventilatory limitation identified a pulmonary process. In 24, deconditioning could not be distinguished from cardiac limitation. Of these, 14 responded to exercise training and/or weight loss, whereas 3 had cardiac disease, 7 had HAD, and 4 had psychogenic dyspnea (4 had more than one clinical diagnosis). In the 13 patients with normal CPET results, one had gastroesophageal reflux, two had HAD, four had psychogenic dyspnea, and six had no identifiable disease. We conclude that a diagnosis can be made in most patients with chronic dyspnea; however, further studies including bronchoprovocation are often required. Cardiopulmonary exercise testing is useful in identifying a cardiac or pulmonary process, but it is insensitive in distinguishing cardiac disease from deconditioning. 相似文献
89.
The k-nearest-neighbour (kNN) algorithm is widely applied for the estimation of forest attributes using remote sensing data. It requires a large amount of reference data to achieve satisfactory results. Usually, the number of available reference plots for the kNN-prediction is limited by the size of the area covered by a terrestrial reference inventory and remotely sensed imagery collected from one overflight. The applicability of kNN could be enhanced if adjacent images of different acquisition dates could be used in the same estimation procedure. Relative radiometric calibration is a prerequisite for this. This study focuses on two empirical calibration methods. They are tested on adjacent LANDSAT TM scenes in Austria. The first, quite conventional one is based on radiometric control points in the overlap area of two images and on the determination of transformation parameters by linear regression. The other, recently developed method exploits the kNN-cross-validation procedure. Performance and applicability of both methods as well as the impact of phenology are discussed. 相似文献
90.
OBJECTIVE: Hyaluronate degradation was analyzed in cultures of healthy tissue and tissue obtained from patients with rheumatoid arthritis. METHODS: Arthritic and healthy synovial tissues were incubated in culture with [3H]glucosamine. Labelled hyaluronate was extracted and its size determined by gel filtration. The production of low molecular weight hyaluronate was analyzed by pulse-chase experiments. Radical production was measured by a cytochrome C reduction assay. RESULTS: Healthy tissues and some arthritic tissues that did not contain significant amounts of granulocytes produced high molecular weight hyaluronate. In contrast, arthritic tissue infiltrated with granulocytes released low molecular weight hyaluronate. Pulse-chase experiments suggested that hyaluronate was degraded in these arthritic tissues. Exogenous hyaluronate was degraded only by intact tissue, but not by cells in culture obtained from synovial membranes of synovial fluids. Hyaluronate degradation was accompanied by massive oxygen radical production. Radical scavengers protected hyaluronate from degradation in synovial tissue. Some protection was achieved by superoxide and catalase or by methionine and complete protection by the iron chelators diethyltriaminepentacetic acid or deferoxamine mesylate. CONCLUSION: Degradation of hyaluronate in arthritic synovial tissue may be inhibited in tissue culture by radical scavengers. 相似文献