全文获取类型
收费全文 | 777221篇 |
免费 | 9309篇 |
国内免费 | 1772篇 |
专业分类
电工技术 | 14453篇 |
综合类 | 844篇 |
化学工业 | 119172篇 |
金属工艺 | 33868篇 |
机械仪表 | 25712篇 |
建筑科学 | 17823篇 |
矿业工程 | 5218篇 |
能源动力 | 19328篇 |
轻工业 | 61665篇 |
水利工程 | 9068篇 |
石油天然气 | 17102篇 |
武器工业 | 98篇 |
无线电 | 86469篇 |
一般工业技术 | 157905篇 |
冶金工业 | 132087篇 |
原子能技术 | 17722篇 |
自动化技术 | 69768篇 |
出版年
2021年 | 6640篇 |
2019年 | 6357篇 |
2018年 | 15064篇 |
2017年 | 15367篇 |
2016年 | 14287篇 |
2015年 | 7673篇 |
2014年 | 12644篇 |
2013年 | 33828篇 |
2012年 | 20898篇 |
2011年 | 30806篇 |
2010年 | 25370篇 |
2009年 | 27197篇 |
2008年 | 28010篇 |
2007年 | 28890篇 |
2006年 | 21397篇 |
2005年 | 21106篇 |
2004年 | 19589篇 |
2003年 | 19242篇 |
2002年 | 17950篇 |
2001年 | 17152篇 |
2000年 | 16500篇 |
1999年 | 16283篇 |
1998年 | 38003篇 |
1997年 | 27410篇 |
1996年 | 21554篇 |
1995年 | 16603篇 |
1994年 | 14921篇 |
1993年 | 14673篇 |
1992年 | 11559篇 |
1991年 | 10970篇 |
1990年 | 10792篇 |
1989年 | 10396篇 |
1988年 | 9965篇 |
1987年 | 8977篇 |
1986年 | 8713篇 |
1985年 | 9949篇 |
1984年 | 9064篇 |
1983年 | 8571篇 |
1982年 | 7859篇 |
1981年 | 7988篇 |
1980年 | 7552篇 |
1979年 | 7578篇 |
1978年 | 7380篇 |
1977年 | 8297篇 |
1976年 | 10363篇 |
1975年 | 6677篇 |
1974年 | 6517篇 |
1973年 | 6638篇 |
1972年 | 5527篇 |
1971年 | 5178篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
A crack-tip screening analysis of cleavage fracture of steel is developed. The analysis incorporates evidence that reinitiation
of an arrested cleavage crack requires less stress intensity than cleavage initiation from a fatigue precrack. Fractographic
evidence as well as metallographic sectioning of arrested cracks have previously shown that the mechanism of rapid crack propagation
by cleavage is affected strongly by partial crack-plane deflection which leaves unbroken ligaments in its wake. The tearing
of these ligaments by dimple rupture is the dominant energy-absorbing mechanism. Earlier etch-pit experiments using an Fe-Si
alloy showed that the crack-tip stress intensity based on plastic zone size is extremely low. These observations are incorporated
into a model in which cleavage crack reinitiation is analyzed using a sharp crack that is shielded by a distribution of pinching
forces along its faces. During reloading of the arrested crack, the ligaments restrict crack-tip blunting, leading to higher
local stresses. As a result, lower stress intensities are needed for reinitiation than for initiation from a fatigue precrack. 相似文献
952.
953.
954.
G. Mentzas 《欧洲信息系统杂志》1991,1(3):193-203
The purpose of this paper is to provide an analysis of the alternative modelling systems for office information systems. More specifically, we are interested in identifying the current research trends of merging office modelling ideas together with concepts that owe their origin to the object-oriented paradigm and to artificial intelligence. In this respect an office model is defined as encompassing three domains: passive office objects; dynamically defined and manipulated office procedures; and goal-directed office tasks. Following this definition we exploit the potential of using the object-oriented and knowledge representation techniques for modelling each of the three domains using evidence from real-world applications. 相似文献
955.
W. S. Walston I. M. Bernstein A. W. Thompson 《Metallurgical and Materials Transactions A》1991,22(6):1443-1451
The microstructure of a single-crystal nickel-base superalloy, PWA 1480, has been varied by heat treatment and hot isostatic
pressing in order to study the role of the γ/yγ′ eutectic and porosity on subsequent tensile behavior. The level of porosity
was found not to affect any of the tensile properties, while the γ/γ′ eutectic strongly influenced ductility. Eliminating
the γ/γ′ eutectic increased ductility which was attributed to the cleavage fracture of this constituent. It is proposed that
such cleavage of the γ/γ′ eutectic is initiated by the stress created from impinging slip bands, promoting shear localization,
and final fracture along {111} slip planes. The precise nature of this fracture process is discussed with emphasis on the
role of the γ/′ micro-structure. The deformation structure of PWA 1480 was also studied, and while different in some respects
from many other single-crystal superalloys, its fracture process appears to be similar.
Formerly Graduate Student, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University. 相似文献
956.
957.
958.
959.
T. A. Hall 《Journal of microscopy》1991,164(1):67-79
When a microregion in a thin section of frozen-dried and embedded tissue is analysed by the conventional electron-probe X-ray continuum-normalization method, the measured quantity is in mmol of element per kg of embedded specimen. As each microregion contains an unknown amount of embedding medium, this quantity generally lies indeterminately somewhere within the wide range between mmol of element per kg of hydrated tissue and mmol of element per kg of dehydrated tissue. However, if a ‘tag’ element is incorporated in the embedding medium, the contribution of the medium to the local continuum count in each probed field should be measurable, and the X-ray data may then unambiguously yield mmol of element per kg of dehydrated tissue. This result should not be affected by shrinkage on freeze-drying or by incomplete replacement of water by embedding medium. The same X-ray data can additionally provide estimates of mmol of element per unit volume, mmol of element per kg of hydrated tissue and local dry-mass fraction. However, these estimates are subject to errors due to tissue shrinkage, incomplete replacement of water and beam damage. 相似文献
960.