全文获取类型
收费全文 | 457368篇 |
免费 | 30284篇 |
国内免费 | 16886篇 |
专业分类
电工技术 | 22815篇 |
技术理论 | 46篇 |
综合类 | 28483篇 |
化学工业 | 73861篇 |
金属工艺 | 26463篇 |
机械仪表 | 26772篇 |
建筑科学 | 31673篇 |
矿业工程 | 12977篇 |
能源动力 | 11334篇 |
轻工业 | 28634篇 |
水利工程 | 8388篇 |
石油天然气 | 25289篇 |
武器工业 | 2973篇 |
无线电 | 49665篇 |
一般工业技术 | 56763篇 |
冶金工业 | 22218篇 |
原子能技术 | 4125篇 |
自动化技术 | 72059篇 |
出版年
2024年 | 1523篇 |
2023年 | 5876篇 |
2022年 | 10450篇 |
2021年 | 14737篇 |
2020年 | 11166篇 |
2019年 | 9079篇 |
2018年 | 23315篇 |
2017年 | 23685篇 |
2016年 | 19725篇 |
2015年 | 15234篇 |
2014年 | 18782篇 |
2013年 | 22467篇 |
2012年 | 27022篇 |
2011年 | 35347篇 |
2010年 | 31181篇 |
2009年 | 27440篇 |
2008年 | 28168篇 |
2007年 | 28276篇 |
2006年 | 21538篇 |
2005年 | 19923篇 |
2004年 | 13750篇 |
2003年 | 12501篇 |
2002年 | 11035篇 |
2001年 | 9436篇 |
2000年 | 9468篇 |
1999年 | 10140篇 |
1998年 | 7837篇 |
1997年 | 6711篇 |
1996年 | 6335篇 |
1995年 | 5194篇 |
1994年 | 4198篇 |
1993年 | 2858篇 |
1992年 | 2256篇 |
1991年 | 1732篇 |
1990年 | 1336篇 |
1989年 | 1085篇 |
1988年 | 910篇 |
1987年 | 571篇 |
1986年 | 454篇 |
1985年 | 280篇 |
1984年 | 226篇 |
1983年 | 177篇 |
1982年 | 143篇 |
1981年 | 86篇 |
1980年 | 101篇 |
1968年 | 46篇 |
1966年 | 46篇 |
1965年 | 45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
131.
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
132.
133.
134.
本文以硼酸铝晶须为增强剂,以4,5-环氧环己烷-1,2-二甲酸二缩水甘油酯(TDE-85),甲基纳狄克酸酐(MNA)、N,N’-二胺基二苯甲烷型双马来酰亚胺(BMI)/O,O′-二烯丙基双酚A(BA)体系分别作为基体制备晶须增强复合材料。研究了晶须对树脂的尺寸、表面处理方法、含量对树脂体系力学性能和热性能的影响;通过扫描电子显微镜(SEM)分析了浇注体的弯曲、冲击断口,研究晶须的增强机理。 相似文献
135.
李凯花 《石油化工管理干部学院学报》2003,(4):19-21
推进施工企业党组织的建设必须与时俱进,坚持一岗双责、两个融合、三个同步、四个同时,创新工作思路、工作机制、工作方法和工作方式。把贯彻落实“三个代表”重要思想,作为检验工作成效的根本标准。 相似文献
136.
Analysis on the effectiveness of the 20-H rule for printed-circuit-board layout to reduce edge-radiated coupling 总被引:1,自引:0,他引:1
Montrose M.I. Er-Ping Li Hong-Fang Jin Wei-Liang Yuan 《Electromagnetic Compatibility, IEEE Transactions on》2005,47(2):227-233
This paper presents the quantified study of the electromagnetic radiation mechanism of the 20-H rule using a numerical approach that has not yet been systematically addressed. The 20-H rule is a rule-of-thumb layout technique recommended to minimize radiated fields propagating from the edges of a printed circuit board (PCB) coupling onto nearby structures. Propagating electromagnetic fields may corrupt adjacent cable assemblies, sheet metal enclosures, and aperture openings. The magnitude of this design rule is investigated using the full-wave finite-difference time-domain (FDTD) method. An analysis on whether benefits exist from use of this rule is examined and under what conditions the rule is valid when correctly implemented. The purpose of this paper is to provide insight into the validity of the 20-H rule, recognizing that every PCB will have different simulation results. FDTD is used to capture a snapshot view of field propagation. This view allows one to determine the validity of the 20-H rule at a single point of time within a dynamic structure and what may be expected when digital components are finally added to a PCB assembly, which generally negates simulated results. 相似文献
137.
Hong Wang Rong Zeng Xiuping Li 《Microwave Theory and Techniques》2005,53(2):564-570
In this paper, RF noise in 0.18-mum NMOSFETs concerning the contribution of carrier heating and hot carrier effect is characterized and analyzed in detail via a novel approach that modulates the channel carrier heating and number of hot carriers using body bias. We confirm qualitatively a negligible role of hot carrier effect on the channel noise in deep-submicrometer MOSFETs. For a device under reverse body bias (Vb), even though the increase in hot carrier population is clearly characterized by dc measurements, the device high-frequency noise is found to be irrelevant to the increase in the channel hot carriers. Experimental results show that the high-frequency noise is slightly reduced with the increase in |Vb|, and can be qualitatively explained by secondary effects such as the suppression of nonequilibrium channel noise and substrate induced noise. The reduction of NFmin and Rn with the increase in |Vb| may provide a possible methodology to finely adjust the device high-frequency noise performance for circuit design 相似文献
138.
139.
140.
Jon T. Carter Paul E. Krajewski Ravi Verma 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(11):77-81
The hot blow forming of magnesium sheet offers significant opportunity for forming complex, lightweight parts for automotive
applications. This paper characterizes the elevated-temperature formability of AZ31 magnesium sheet materials and the effect
of processing conditions on the performance of these materials. In addition, magnesium sheet application development at General
Motors Corporation is reviewed. 相似文献