全文获取类型
收费全文 | 90404篇 |
免费 | 1179篇 |
国内免费 | 413篇 |
专业分类
电工技术 | 833篇 |
综合类 | 2319篇 |
化学工业 | 12714篇 |
金属工艺 | 4919篇 |
机械仪表 | 3158篇 |
建筑科学 | 2552篇 |
矿业工程 | 574篇 |
能源动力 | 1319篇 |
轻工业 | 4277篇 |
水利工程 | 1374篇 |
石油天然气 | 372篇 |
无线电 | 9702篇 |
一般工业技术 | 17457篇 |
冶金工业 | 3849篇 |
原子能技术 | 302篇 |
自动化技术 | 26275篇 |
出版年
2022年 | 81篇 |
2021年 | 107篇 |
2020年 | 102篇 |
2019年 | 104篇 |
2018年 | 14538篇 |
2017年 | 13470篇 |
2016年 | 10065篇 |
2015年 | 736篇 |
2014年 | 419篇 |
2013年 | 606篇 |
2012年 | 3469篇 |
2011年 | 9798篇 |
2010年 | 8554篇 |
2009年 | 5849篇 |
2008年 | 7191篇 |
2007年 | 8112篇 |
2006年 | 426篇 |
2005年 | 1540篇 |
2004年 | 1380篇 |
2003年 | 1406篇 |
2002年 | 761篇 |
2001年 | 220篇 |
2000年 | 277篇 |
1999年 | 175篇 |
1998年 | 216篇 |
1997年 | 141篇 |
1996年 | 192篇 |
1995年 | 122篇 |
1994年 | 115篇 |
1993年 | 104篇 |
1992年 | 92篇 |
1991年 | 85篇 |
1990年 | 65篇 |
1989年 | 89篇 |
1988年 | 63篇 |
1987年 | 57篇 |
1986年 | 56篇 |
1985年 | 67篇 |
1984年 | 64篇 |
1983年 | 59篇 |
1982年 | 48篇 |
1981年 | 52篇 |
1979年 | 41篇 |
1968年 | 48篇 |
1966年 | 47篇 |
1965年 | 44篇 |
1958年 | 38篇 |
1957年 | 36篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
Marginal costs of electricity vary by time and location. In the past, researchers attributed the variations to factors related to electricity generation and transmission. These authors, however, have not analyzed possible variations in marginal distribution capacity costs (MDCC). The objectives of this paper are:
- 1. (i) to show that large MDCC variations are due to the dispersion in distribution capital expenditures by time and space,
- 2. (ii) to propose a method for quantifying the area- and time-specific MDCC in the presence of lumpy investments, and
- 3. (iii) to compare our MDCC estimates to those commonly used in the electric utility industry.
33.
Letters to the editor 总被引:1,自引:0,他引:1
34.
35.
Three interesterified vegetable oils (IVOs) prepared from palm, cottonseed, and olive oil, respectively, have been studied for application to Frankfurters. Beef fat (10%) was replaced by one of the IVOs at 20, 60 or 100%. Fatty acid composition of the lipid fraction in the Frankfurters and saturated/unsaturated ratios were established for all batches. We found that total or partial replacement of beef fat by IVOs did not lead to significant changes in appearance, colour, texture, flavour or sensory score. We conclude that IVOs may be successfully applied as beef fat substitutes in Frankfurters. 相似文献
36.
J-M Choe 《欧洲信息系统杂志》2002,11(2):142-158
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms. 相似文献
37.
Brian M. Louie Thomas Franaszek Tina Pho Wen Yen Chiu David S. Soong 《应用聚合物科学杂志》1985,30(9):3841-3856
Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate. 相似文献
38.
Less may not be more,but it still counts: The state of social capital in Yeoville,Johannesburg 总被引:2,自引:2,他引:0
Kirsten Harrison 《Urban Forum》2002,13(1):67-84
39.
Yanqiu Shao Jiqing Han Ting Liu Yongzhen Zhao 《International Journal of Speech Technology》2007,10(1):45-55
In real speech, not like lexical words (LWs), prosodic words (PWs) are basic rhythmic units. The naturalness of a Text-to-Speech
(TTS) system is directly influenced by the segmentation of the PWs. Most of the PWs are the combination of several LWs. In
this paper, three Lexical Combination Models are proposed to combine LWs into PWs, including a Directed Acyclic Graph Model,
a Segmentation Model and a Markov Model (MM). To cope with the situation where some long LWs should be segmented into two
or more PWs, a Lexical Split Model (LSM) is applied to the long LWs. Experimental results prove that relatively constant results
with various training data can be obtained from a MM. The Transformation-Based Error Driven Learning (TBED) algorithm, for
its high performance of individual property, is applied in combination with the MM to improve the precision of PW segmentation.
Experiments show that among the three proposed models, the MM combined with TBED and LSM, leads to the best performance, in
which a precision of 93.00% and a recall of 93.23% are achieved. The perception test indicates that by using PWs as the lowest
prosodic units a speech sounds more natural and acceptable than by using LWs.
This paper is supported by NSFC Project (60503071); 973 Natural Basic Research Program of China (2004CB318102); Postdoctor
Science Foundation of P. R. China (20070420275). 相似文献
40.
In this paper we describe, from a theoretical point of view, critical configurations for the projective reconstruction of
a set of points, for a single view, i.e. for calibration of a camera, in the case of projections from ℙk to ℙ2 for k ≥ 4. We give first a general result describing these critical loci in ℙk, which, if irreducible, are algebraic varieties of dimension k−2 and degree 3. If k=4 they can be either a smooth ruled surface or a cone and if k = 5 they can be a smooth three dimensional variety, ruled in planes, or a cone. If k≥ 6, the variety is always a cone, the
vertex of which has dimension at least k − 6. The reducible cases are studied in Appendix A.
These results are then applied to determine explicitly the critical loci for the projections from ℙk which arise from the dynamic scenes in ℙ3 considered in [13].
Marina Bertolini is currently Associate Professor of Geometry at the Department of Mathematics at the Università degli Studi di Milano, Italy.
Her main field of research is Complex Projective Algebraic Geometry, with particular interest for the classification of projective
varieties and for the geometry of Grassmann varieties. On these topics M. Bertolini has published more than twenty reviewed
papers on national and international journals. She has been for some years now interested also in applications of Algebraic
Geometry to Computer Vision problems.
Cristina Turrini is Associate Professor of Geometry at the Department of Mathematics of Università degli Studi di Milano, Italy. Her main
research interest is Complex Projective Algebraic Geometry: subvarieties of Grassmannians, special varieties, automorphisms,
classification. In the last two years she has started to work on applications of Algebraic Geometry to problems of Computer
Vision. She is author or co-author of about thirty reviewed papers. She is also involved in popularization of Mathematics,
and on this subject she is co-editor of some books. 相似文献