全文获取类型
收费全文 | 277638篇 |
免费 | 3501篇 |
国内免费 | 1304篇 |
专业分类
电工技术 | 4800篇 |
综合类 | 519篇 |
化学工业 | 40245篇 |
金属工艺 | 11123篇 |
机械仪表 | 8414篇 |
建筑科学 | 6393篇 |
矿业工程 | 1575篇 |
能源动力 | 6966篇 |
轻工业 | 22456篇 |
水利工程 | 3035篇 |
石油天然气 | 5781篇 |
武器工业 | 43篇 |
无线电 | 33487篇 |
一般工业技术 | 56433篇 |
冶金工业 | 50863篇 |
原子能技术 | 7489篇 |
自动化技术 | 22821篇 |
出版年
2021年 | 2151篇 |
2019年 | 2060篇 |
2018年 | 3574篇 |
2017年 | 3668篇 |
2016年 | 3897篇 |
2015年 | 2484篇 |
2014年 | 4344篇 |
2013年 | 11956篇 |
2012年 | 7060篇 |
2011年 | 9699篇 |
2010年 | 7530篇 |
2009年 | 8744篇 |
2008年 | 9091篇 |
2007年 | 9129篇 |
2006年 | 7800篇 |
2005年 | 7246篇 |
2004年 | 7196篇 |
2003年 | 6972篇 |
2002年 | 6713篇 |
2001年 | 6844篇 |
2000年 | 6476篇 |
1999年 | 6760篇 |
1998年 | 16295篇 |
1997年 | 11579篇 |
1996年 | 8915篇 |
1995年 | 6844篇 |
1994年 | 6012篇 |
1993年 | 6051篇 |
1992年 | 4395篇 |
1991年 | 4180篇 |
1990年 | 4073篇 |
1989年 | 4055篇 |
1988年 | 3750篇 |
1987年 | 3387篇 |
1986年 | 3392篇 |
1985年 | 3739篇 |
1984年 | 3460篇 |
1983年 | 3217篇 |
1982年 | 3024篇 |
1981年 | 3038篇 |
1980年 | 3030篇 |
1979年 | 2829篇 |
1978年 | 2869篇 |
1977年 | 3141篇 |
1976年 | 4096篇 |
1975年 | 2416篇 |
1974年 | 2379篇 |
1973年 | 2396篇 |
1972年 | 2018篇 |
1971年 | 1781篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
921.
922.
S. Bismo P. Duverneuil L. Pibouleau S. Domenech J. -P. Couderc 《Materials and Manufacturing Processes》1995,10(2):241-266
This paper presents the results of our work on a new type of CVD reactor, annular reactor. This equipment is able to deposit pure silicon and also in-situ phosphorus doped silicon on a large number of substrates 相似文献
923.
M. Bethmont Y. Meyzaud P. Soulat 《International Journal of Pressure Vessels and Piping》1996,65(3):221-229
Primary piping elbows of ligh water reactors are made of cast austeno-ferritic materials (grade CF8 or CF8M) which are susceptible to embrittlement by thermal ageing in service. Ageing kinetics depends on chromium content and on the temperature. The effect of ageing on mechanical properties is determined by the decreasing of Charpy-U energy. It is shown that the rupture of such aged material comes from a combination of cleavage of the ferrite and shearing or ductile tearing of austenite ligaments. The fracture toughness is determined by J-R curves, which exhibit a large scatter related to the solidification macrostructure of the steel. It is shown that J-R curves are independent of the geometry of the specimens. 相似文献
924.
Piquemal F.P.M. Trapon G.R. Geneves G.P.J. 《IEEE transactions on instrumentation and measurement》1996,45(6):918-922
AC measurements of the longitudinal resistance, Rxx, of a quantum Hall effect (QHE) sample have been made in a frequency range from 10 Hz to 10 kHz. The results show no frequency effect on the minimum value of Rxx corresponding to the quantum numbers i=2 and i=4, within the measurement resolution of 0.5 mΩ. Therefore, the influence of frequency on the value of the quantized Hall resistance, RH, should not exceed a few parts in 109 . Some unwanted effects detected during the development of the resistance bridge have been pointed out 相似文献
925.
Summary Small oscillations of a rotating elasticum with a mass at the free end are investigated with Poincaré-Lindstedt series. It is shown that the mass moves on a figure-eight shaped curve in a direction determined by the sign of the angular velocity and hence that the Coriolis force influences the motion. 相似文献
926.
Froggatt M.E. Allison S.G. Moore J.P. 《IEEE transactions on instrumentation and measurement》1996,45(1):123-126
This paper presents a method of correcting for unwanted phase shifts introduced by interchanging ultrasonic transducers and other measurement system components when using the pulsed phase-locked loop (PPLL) ultrasonic system. Theory is derived mathematically separating phase errors into their constituents. The relationship to a previously derived method of determining the number of periods into the tone-burst, at which the system samples, is established, and a method of adjusting this number to be an integer is presented. Implementation of the technology on a computer is demonstrated through experimental results on transducers of differing frequencies and diameters. Sensitivity to path-length is tested. This work has resulted in a straightforward means of calibrating transducers in conjunction with PPLL measurements using a single, fixed reference block 相似文献
927.
Fractal geometry is finding its application in the nondestructive evaluation (NDE) of corrosion by characterizing the corrosion surface with fractal dimensions. It was found that corrosion surfaces can be well described by multifractals. Two algorithms were used to obtain the fractal dimensions of a corroded aluminum alloy surface, one being box-counting and another being coherent light scattering. Fractal dimensions were related with the damage caused by corrosion and fatigue. 相似文献
928.
929.
As a consequence of the phasing out of CFCs, sorption systems appear to be potential candidates to replace vapour compression systems. Amongst sorption systems there exists a choice between several systems, such as liquid absorption, solid adsorption and chemical reaction heat pumps. Nevertheless, few comparative studies between these systems have been undertaken so far. It is the aim of this paper to present such a study based on combined first and second law thermodynamical analysis of the different cycles. Simple entropy generation processes explain why the basic cycles for these systems yield performances much lower than the Carnot efficiency. The possibility of operating regenerative cycles with internal heat recovery and higher efficiencies has also been considered for typical common base conditions. Different entropy generation considerations have been visualised, such as thermal coupling (external/internal), non-uniform temperature component entropy production and other irreversible processes for the COP degradation in these systems. It is found that thermal coupling irreversibilities in solid sorption systems and other internal irreversibilities in liquid sorption systems with solution heat exchanger are dominant in the actual COP degradation with respect to the reversible Carnot COP. 相似文献
930.
A cryo-specimen storage system for low-temperature scanning electron microscopy (LTSEM) specimens is described, which: liberates multi-specimen experiments from sampling restrictions imposed by the rate at which LTSEM specimens can be examined in the SEM; provides security against experiment loss resulting from breakdown of the SEM or cryo-system; enables collection of specimens in the field or in laboratories remote from the SEM laboratory; and facilitates international air transport of LTSEM specimens. The components of the system, which has a capacity of 98 stub-mounted specimens, are readily made in a laboratory workshop. The details of the design may be altered to suit particular specimen types or experimental approaches. 相似文献