全文获取类型
收费全文 | 845789篇 |
免费 | 10025篇 |
国内免费 | 2592篇 |
专业分类
电工技术 | 14672篇 |
综合类 | 3261篇 |
化学工业 | 127782篇 |
金属工艺 | 37215篇 |
机械仪表 | 28192篇 |
建筑科学 | 19635篇 |
矿业工程 | 5842篇 |
能源动力 | 20703篇 |
轻工业 | 63890篇 |
水利工程 | 10183篇 |
石油天然气 | 18613篇 |
武器工业 | 76篇 |
无线电 | 92165篇 |
一般工业技术 | 171725篇 |
冶金工业 | 135900篇 |
原子能技术 | 18963篇 |
自动化技术 | 89589篇 |
出版年
2021年 | 6789篇 |
2019年 | 6457篇 |
2018年 | 26336篇 |
2017年 | 25624篇 |
2016年 | 22084篇 |
2015年 | 8248篇 |
2014年 | 13046篇 |
2013年 | 34376篇 |
2012年 | 23420篇 |
2011年 | 38006篇 |
2010年 | 31397篇 |
2009年 | 31555篇 |
2008年 | 32987篇 |
2007年 | 34346篇 |
2006年 | 21320篇 |
2005年 | 21789篇 |
2004年 | 20519篇 |
2003年 | 20073篇 |
2002年 | 18497篇 |
2001年 | 17421篇 |
2000年 | 16725篇 |
1999年 | 16706篇 |
1998年 | 39218篇 |
1997年 | 28346篇 |
1996年 | 21987篇 |
1995年 | 16927篇 |
1994年 | 15171篇 |
1993年 | 14972篇 |
1992年 | 11374篇 |
1991年 | 11050篇 |
1990年 | 10748篇 |
1989年 | 10500篇 |
1988年 | 10001篇 |
1987年 | 9050篇 |
1986年 | 8869篇 |
1985年 | 9947篇 |
1984年 | 9076篇 |
1983年 | 8601篇 |
1982年 | 7814篇 |
1981年 | 7935篇 |
1980年 | 7663篇 |
1979年 | 7588篇 |
1978年 | 7536篇 |
1977年 | 8301篇 |
1976年 | 10557篇 |
1975年 | 6675篇 |
1974年 | 6407篇 |
1973年 | 6481篇 |
1972年 | 5522篇 |
1971年 | 5074篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
P. F. Prasolov 《Strength of Materials》1991,23(3):282-285
Based on the criteria of safety of the spherical portion of the deformation stresses and for the work of deformation on the limiting condition of a material a separation is made of the elastic energy of deformation of an anisotropic body. It is shown that in the general case of loading the components of the spherical portion of the stresses and strains are not equal to one third of their first invariants. The values of these components, as for the values of the deviator portion of the elastic potential, depend upon the stressed and strained state and the loading direction (deformation).Translated from Problemy Prochnosti, No. 3, pp. 38–40, March, 1991. 相似文献
993.
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
994.
J. M. Parpia W. P. Kirk P. S. Kobiela Z. Olejniczak 《Journal of Low Temperature Physics》1985,60(1-2):57-72
The ac susceptibility of lanthanum-diluted cerium magnesium nitrate has been compared to the temperature scales as derived
from the (P, T) relation determined by Halperin and that was measured recently by Greywall. It is found that the susceptibility does
not obey a simple Curie-Weiss law over the temperature range between 1 and 50 mK. The results of these calibrations are also
used to determine the temperatures for the second-order phase transitions into the superfluid phases of3He at several pressures. TheseT
c(P) values are compared to results of earlier experiments that used thermometry based on the susceptibility of platinum as well
as other thermometry techniques. 相似文献
995.
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
996.
997.
998.
999.
Due to their small size, mammalian oocytes and embryos pose unique problems during preparation for transmission electron microscopy. This paper outlines a method which combines protein embedding with centrifugation to locate the specimens on the face of a Beem capsule mould. This method facilitates both the processing of oocytes with minimal loss and rapid location of the specimens within the block for simultaneous sectioning, staining and examination. 相似文献
1000.
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