全文获取类型
收费全文 | 243420篇 |
免费 | 3151篇 |
国内免费 | 1241篇 |
专业分类
电工技术 | 4856篇 |
综合类 | 264篇 |
化学工业 | 35441篇 |
金属工艺 | 10864篇 |
机械仪表 | 7070篇 |
建筑科学 | 6239篇 |
矿业工程 | 481篇 |
能源动力 | 6276篇 |
轻工业 | 24157篇 |
水利工程 | 1836篇 |
石油天然气 | 1335篇 |
武器工业 | 3篇 |
无线电 | 31054篇 |
一般工业技术 | 44888篇 |
冶金工业 | 50128篇 |
原子能技术 | 3868篇 |
自动化技术 | 19052篇 |
出版年
2021年 | 1564篇 |
2019年 | 1426篇 |
2018年 | 2321篇 |
2017年 | 2224篇 |
2016年 | 2444篇 |
2015年 | 1908篇 |
2014年 | 3160篇 |
2013年 | 10796篇 |
2012年 | 5452篇 |
2011年 | 7791篇 |
2010年 | 6292篇 |
2009年 | 6969篇 |
2008年 | 7565篇 |
2007年 | 7664篇 |
2006年 | 7033篇 |
2005年 | 6522篇 |
2004年 | 6245篇 |
2003年 | 6267篇 |
2002年 | 6246篇 |
2001年 | 6377篇 |
2000年 | 5805篇 |
1999年 | 6422篇 |
1998年 | 16569篇 |
1997年 | 11605篇 |
1996年 | 8953篇 |
1995年 | 6690篇 |
1994年 | 5908篇 |
1993年 | 5728篇 |
1992年 | 4054篇 |
1991年 | 3998篇 |
1990年 | 3587篇 |
1989年 | 3507篇 |
1988年 | 3441篇 |
1987年 | 2910篇 |
1986年 | 2842篇 |
1985年 | 3416篇 |
1984年 | 3053篇 |
1983年 | 2747篇 |
1982年 | 2548篇 |
1981年 | 2569篇 |
1980年 | 2431篇 |
1979年 | 2273篇 |
1978年 | 2235篇 |
1977年 | 2809篇 |
1976年 | 4172篇 |
1975年 | 1900篇 |
1974年 | 1797篇 |
1973年 | 1784篇 |
1972年 | 1461篇 |
1971年 | 1317篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
The work-hardening mechanisms in two-phase γ-titanium aluminide alloys were characterized in terms of the glide obstacles determining the velocity and slip path of dislocations,
utilizing transmission electron microscopy (TEM) observations and thermodynamic-glide parameters. There was clear evidence
that short-range obstacles in the form of dislocation debris and dipoles were produced during plastic deformation at room
temperature. These dislocation obstacles contributed significantly to work hardening. The observed strong strain hardening
arose from long-range elastic dislocation interactions and the production of dipole and debris defects. The thermal stability
of these deformation-induced defects was assessed by isothermal and isochronal annealing. The results indicated that the dipole
and debris defects were relatively unstable upon annealing at moderately high temperatures, which led to significant recovery
of work hardening.
This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented
at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint
Committee on Mechanical Behavior of Materials. 相似文献
942.
G. C. Coelho J. A. Golczewski H. F. Fischmeister 《Metallurgical and Materials Transactions A》2003,34(9):1749-1758
Thermodynamical equilibria have been calculated for a wide variety of high-speed steel compositions belonging to the multicomponent
system Fe-C-W-Mo-V-Cr-Nb as well as for two series of white-cast-iron alloys containing niobium. Some temperature-concentration
diagrams for both classes of alloys are presented and calculated quantities (melting and transformation temperatures, amounts
and compositions of phases) are compared with experimental data. Good agreement between calculated and experimental information
has been obtained, with the exception of the MC phase compositions and transformation temperatures for white-cast-iron alloys
with high carbon and chromium contents. These differences can, however, be satisfactorily explained by plausible kinetic effects. 相似文献
943.
944.
Novel floating-patch micro-electro-mechanical system (MEMS) antennas are proposed for millimetre-wave applications. The floating-patch MEMS antennas are fabricated on a high resistivity silicon (HRS) substrate using surface micromachining technology. Simulation and experimental results for reflection coefficients and radiation patterns are presented. 相似文献
945.
X. X. Xi X. H. Zeng A. V. Pogrebnyakov A. Soukiassian S. Y. Xu Y. F. Hu E. Wertz Q. Li Y. Zhong C. O. Brubaker Z.-K. Liu E. M. Lysczek J. M. Redwing J. Lettieri D. G. Schlom W. Tian H. P. Sun X. Q. Pan 《Journal of Superconductivity and Novel Magnetism》2003,16(5):801-806
The recently discovered superconductor MgB2 with T c at 39 K has great potential in superconducting electronics. In this paper, we review the deposition techniques used for MgB2 thin films in the light of a thermodynamic study of the Mg-B system with the calculation of phase diagrams (CALPHAD) modeling technique. This thermodynamic study identifies a growth window in the pressure–temperature phase diagram, in which the magnesium pressure is very high for likely in situ growth temperatures. A Hybrid Physical–Chemical Vapor Deposition (HPCVD) technique that successfully achieves such a high Mg pressure is shown to produce in situ epitaxial MgB2 thin films with bulk superconducting properties. 相似文献
946.
Shuman Daniel W.; Cunningham Mark D.; Connell Mary A.; Reid William H. 《Canadian Metallurgical Quarterly》2003,34(3):233
Forensic psychology has made important gains in professional recognition and stature in the courts, resulting in increasing demands for mobility of expertise. Current regulations regarding the interjurisdictional temporary forensic practice of psychology, however, are characterized by variability of regulations, ambiguity and inaccessibility, and continuing total barriers. A uniform, well-reasoned policy is needed. A conceptual basis for such a policy is provided by a discussion of licensing rationales and the application of these to forensic practice. Uniformity, public and professional protection, and practicability are identified as fundamental regulatory criteria. A Model Rule Regarding the Temporary Forensic Practice of Psychology is proposed for adoption by state licensing boards on a nationwide basis. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
947.
Nickel-rich β-NiAl alloys, which are potential materials for high-temperature shape-memory alloys, show a thermoelastic martensitic transformation,
which produces their shape memory effect. However, the transformation to Ni5Al3 phase during heating of NiAl martensite can interrupt the reversible martensitic transformation; consequently, the shape
memory effect in NiAl martensite might not appear after heating. The phase transformation process in binary Ni-(34 to 37)Al
martensite was investigated by differential thermal analysis (DTA) method, and we found that the condition of reversible martensitic
transformation was not the β → Ni5Al3 transformation, but rather the M → Ni5Al3 transformation occurring at 250 °C to 300 °C. Therefore, the transformation temperature of M → Ni5Al3 determined the highest operating temperature for the shape memory effect. For verifying the critical temperature, the phase
transformation process was investigated for eight ternary Ni-33Al-X alloys (X=Cu, Co, Fe, Mn, Cr, Ti, Si, and Nb). Only Ti,
Si, and Nb additions were found to be effective in dropping the M
s temperature, and they facilitated the shape memory effect in Ni-33Al-X alloys. In particular, the addition of Si and Nb raised
the transformation temperature of M → Ni5Al3, a potentially beneficial effect for shape memory at higher temperatures.
This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented
at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint
Committee on Mechanical Behavior of Materials. 相似文献
948.
Influence of Ni Interlayers on the Mechanical Properties of Ti6Al4V/(WC-Co) Friction Welds 总被引:2,自引:0,他引:2
M. Shamanian M. Salehi A. Saatchi T. H. North 《Materials and Manufacturing Processes》2003,18(4):581-598
Ni interlayers were introduced prior to dissimilar friction welding of Ti6Al4V base material to three cemented carbide substrates. The fracture strength of Ti6Al4V/(WC-6 wt% Co) welds were poor and were markedly improved when 20-µm thick Ni interlayers were introduced prior to dissimilar friction welding. These results were only produced when the (WC-6 wt% Co) cermet was electroplated prior to friction welding. When the Ti6Al4V alloy was electroplated prior to friction welding, fractured WC particles and cracking were observed in the (WC-Co) carbide substrate. The fracture strengths of Ti6Al4V/(WC-11 wt% Co) and Ti6Al4V/(WC-24 wt% Co) welds were not improved when 20-µm thick Ni interlayers were introduced prior to friction welding. During mechanical testing, the Ni layer retained at the dissimilar joint interface created a region of weakness. 相似文献
949.
This paper presents experimental and analytical results of four scaled prestressed concrete box-girder bridges with corrugated steel webs. The location of prestressing strands at both ends of the specimens and the thickness of end diaphragms are the two major parameters. Based on the experimental results of all four specimens, their seismic behavior is critically examined, including hysteretic loops, ductility factor, dissipated energy, and failure mode, etc. It was found that both the thickness of end diaphragms and the location of prestressing strands at both ends of the specimens are insignificant when the specimens failed at the mid-span due to concrete crushing, and the proposed analytical model can be used to predict the load-displacement relationship of such bridges. 相似文献
950.
Over the last century, IQ scores have been steadily rising, a phenomenon dubbed the Flynn effect. Because of the Flynn effect, IQ tests are periodically renormed, making them harder. Given that eligibility for mental retardation (MR) services relies heavily on IQ scores, renormed tests could have a significant impact on MR placements. In longitudinal IQ records from 9 sites around the country, students in the borderline and mild MR range lost an average of 5.6 points when retested on a renormed test and were more likely to be classified MR compared with peers retested on the same test. The magnitude of the effect is large and affects national policies on education, social security, the death penalty, and the military. This paper reports the perceptions of professionals as they relate to IQ score fluctuations in normal, borderline, and/or MR populations. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献