全文获取类型
收费全文 | 49798篇 |
免费 | 5128篇 |
国内免费 | 3604篇 |
专业分类
电工技术 | 1630篇 |
技术理论 | 1篇 |
综合类 | 5445篇 |
化学工业 | 6054篇 |
金属工艺 | 5698篇 |
机械仪表 | 4043篇 |
建筑科学 | 8114篇 |
矿业工程 | 2938篇 |
能源动力 | 1440篇 |
轻工业 | 2634篇 |
水利工程 | 2366篇 |
石油天然气 | 2827篇 |
武器工业 | 454篇 |
无线电 | 1533篇 |
一般工业技术 | 8260篇 |
冶金工业 | 3062篇 |
原子能技术 | 583篇 |
自动化技术 | 1448篇 |
出版年
2024年 | 175篇 |
2023年 | 638篇 |
2022年 | 1926篇 |
2021年 | 1958篇 |
2020年 | 1539篇 |
2019年 | 1417篇 |
2018年 | 1374篇 |
2017年 | 1692篇 |
2016年 | 1843篇 |
2015年 | 1887篇 |
2014年 | 2765篇 |
2013年 | 3199篇 |
2012年 | 3344篇 |
2011年 | 3601篇 |
2010年 | 2759篇 |
2009年 | 2884篇 |
2008年 | 2724篇 |
2007年 | 3189篇 |
2006年 | 2832篇 |
2005年 | 2466篇 |
2004年 | 2109篇 |
2003年 | 1744篇 |
2002年 | 1567篇 |
2001年 | 1353篇 |
2000年 | 1224篇 |
1999年 | 1025篇 |
1998年 | 846篇 |
1997年 | 753篇 |
1996年 | 648篇 |
1995年 | 561篇 |
1994年 | 475篇 |
1993年 | 372篇 |
1992年 | 352篇 |
1991年 | 241篇 |
1990年 | 216篇 |
1989年 | 199篇 |
1988年 | 130篇 |
1987年 | 103篇 |
1986年 | 72篇 |
1985年 | 55篇 |
1984年 | 50篇 |
1983年 | 33篇 |
1982年 | 47篇 |
1981年 | 11篇 |
1980年 | 20篇 |
1979年 | 24篇 |
1964年 | 12篇 |
1961年 | 7篇 |
1959年 | 19篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
M. Polák M. Majoro F. Hanic J. Pitel M. Kedrová P. Kottman J. Talapa L. Vencel 《Journal of Superconductivity》1989,2(2):219-233
A method for contactless measurement of the shielding critical current density and its dependence on the external magnetic field is described and analyzed. The obtained values are compared with those measured resistively on two different samples. It is shown that the shielding critical current densityJ
cs
and the intergranular transport current densityJ
cr
are identical if the measurement conditions are similar. A degradation ofJ
cs
measured in the external field with AC ripple has been observed. 相似文献
73.
蓝疆号起重铺管船是一艘集起重、管道铺设于一身的多功能新型船舶,在铺管作业系统中,设有一连接船体与托管架的独立结构——拖挂结构。介绍这个由特厚高强钢板组焊而成的结构在制造过程和现场施工中的质量控制及进度控制,供从事工程管理人员参考。 相似文献
74.
75.
地应力对岩心渗透率伤害实验及机理分析 总被引:15,自引:4,他引:11
生产实际情况表明,有许多油气田对应力较为敏感。随着生产的进行,储集层压力下降,有效应力不断变化,引起油藏产能逐渐降低。为研究这一规律和变化规律,阐述了应用岩民测试有效应力对渗透率影响的实验原理,在对实验数据进行统计分析的基础上,拟合出有效应力与渗透经的函数关系(二次多项式)。应用毛细管渗流概念以有弹性厚壁筒厚理,研究了随着毛细管管壁内外压差变化时,毛细管内半径变化有其对毛细管渗流能力的影响,所得结论与实验结果一致。在实际生产中,应控制油藏压力快速大幅度下降,避免有效应力变化引起油藏渗流能力下降和减产。 相似文献
76.
Yield Stress and Microstructure of Set Yogurt Made from High Hydrostatic Pressure-Treated Full Fat Milk 总被引:1,自引:0,他引:1
F. Harte M. Amonte L. Luedecke B.G. Swanson G.V. Barbosa-Cánovas 《Journal of food science》2002,67(6):2245-2250
ABSTRACT: Set yogurts were prepared from fortified milk subjected to the following processes: (a) Thermal process (85C,°C,35 min), (b) High hydrostatic pressure process (193 or 676 MPa for 5 or 30 min), and (c) Nonprocessed milk (control). Yogurts from milk treated with 676 MPa for 30 min exhibited similar yield stress and water-holding capacity (WHC) to yogurts from heated milk. Transmission Electron Microscopy (TEM) micrographs exhibited small round casein micelle aggregates without appendages in yogurts from heated milk. Yogurts from milk treated with 193 MPa and untreated milk exhibited low yield stress, low WHC, and large clusters of coalesced micelles. Mechanisms for gel formation are discussed. 相似文献
77.
On the basis of generalization of the results of investigation of the operation of rodlike elements of composite materials, we make a conclusion that the influence of various factors on the deformability of these elements is studied incompletely. The comparison of the stress-strain states for different models of concrete and reinforced-concrete elements makes it possible to describe the effect of longitudinal reinforcement (coefficient of reinforcement, strength and deformation characteristics) on the critical level of strains in the cross section. According to the results of our investigations, we give recommendations concerning the evaluation of the critical value of the coefficient of reinforcement above which one may observe the effect of reinforcement on the deformability of the analyzed sections. It is shown that the compression strength of the brittle base of the composite with inhomogeneous structure decreases as a result of the fracture processes. It is also demonstrated that the existing procedure used for the evaluation of the indicated decrease in strength requires significant improvement. The problem of evaluation of the ultimate value of the coefficient of reinforcement is also analyzed. 相似文献
78.
80.
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