全文获取类型
收费全文 | 262529篇 |
免费 | 3259篇 |
国内免费 | 825篇 |
专业分类
电工技术 | 5152篇 |
综合类 | 338篇 |
化学工业 | 38169篇 |
金属工艺 | 10299篇 |
机械仪表 | 8531篇 |
建筑科学 | 6312篇 |
矿业工程 | 1084篇 |
能源动力 | 6457篇 |
轻工业 | 23073篇 |
水利工程 | 2576篇 |
石油天然气 | 3910篇 |
武器工业 | 72篇 |
无线电 | 34854篇 |
一般工业技术 | 50375篇 |
冶金工业 | 46688篇 |
原子能技术 | 5453篇 |
自动化技术 | 23270篇 |
出版年
2021年 | 2088篇 |
2019年 | 2057篇 |
2018年 | 3507篇 |
2017年 | 3555篇 |
2016年 | 3791篇 |
2015年 | 2377篇 |
2014年 | 4104篇 |
2013年 | 11390篇 |
2012年 | 6651篇 |
2011年 | 8995篇 |
2010年 | 7074篇 |
2009年 | 7950篇 |
2008年 | 8771篇 |
2007年 | 8696篇 |
2006年 | 7895篇 |
2005年 | 7219篇 |
2004年 | 6950篇 |
2003年 | 6775篇 |
2002年 | 6422篇 |
2001年 | 6518篇 |
2000年 | 6224篇 |
1999年 | 6318篇 |
1998年 | 14310篇 |
1997年 | 10330篇 |
1996年 | 8164篇 |
1995年 | 6465篇 |
1994年 | 5763篇 |
1993年 | 5617篇 |
1992年 | 4590篇 |
1991年 | 4252篇 |
1990年 | 4081篇 |
1989年 | 3820篇 |
1988年 | 3651篇 |
1987年 | 3202篇 |
1986年 | 3097篇 |
1985年 | 3636篇 |
1984年 | 3412篇 |
1983年 | 3060篇 |
1982年 | 2869篇 |
1981年 | 2981篇 |
1980年 | 2785篇 |
1979年 | 2670篇 |
1978年 | 2518篇 |
1977年 | 2967篇 |
1976年 | 3573篇 |
1975年 | 2337篇 |
1974年 | 2334篇 |
1973年 | 2341篇 |
1972年 | 1858篇 |
1971年 | 1759篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Field R. D. Hartwig K. T. Necker C. T. Bingert J. F. Agnew S. R. 《Metallurgical and Materials Transactions A》2002,33(13):965-972
The equal-channel angular extrusion (ECAE) technique has been applied to a powder metallurgy (P/M) source Be alloy. Extrusions
have been successfully completed on Ni-canned billets of Be at approximately 425°C. No cracking was observed in the billets,
and significant grain refinement was achieved. In this article, microstructural features and dislocation structures are discussed
for a singlepass extrusion, including evidence of <c> and <c+a> dislocations. Significant crystallographic texture developed during ECAE, which is discussed in terms of this unique deformation
processing technique and the underlying physical processes which sustain the deformation.
S.R. AGNEW, formerly with the Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
172.
It is essential in the simulation of power electronics applications to model magnetic components accurately. In addition to modeling the nonlinear hysteresis behavior, eddy currents and winding losses must be included to provide a realistic model. In practice the losses in magnetic components give rise to significant temperature increases which can lead to major changes in the component behavior. In this paper a model of magnetic components is presented which integrates a nonlinear model of hysteresis, electro-magnetic windings and thermal behavior in a single model for use in circuit simulation of power electronics systems. Measurements and simulations are presented which demonstrate the accuracy of the approach for the electrical, magnetic and thermal domains across a variety of operating conditions, including static thermal conditions and dynamic self heating 相似文献
173.
A quantum well (QW) in the simultaneous presence of a terahertz field polarized in the growth direction and an incident optical field near an excitonic resonance results in substantial frequency mixing between the terahertz and optical fields. In particular, a response at new frequencies given by the input optical frequency plus or minus multiples of the terahertz frequency occurs-the terahertz sidebands. In a symmetric QW, the dominant contribution to terahertz-sideband formation is the high-frequency modulation of the overlap integral of the relevant conduction- and valence-subband envelope functions that determine the strength of the interband dipole moment. terahertz-sideband generation is shown to be strongly enhanced in a high quality-factor optical microcavity. Numerical values of the reflected intensity into the first terahertz sideband normalized with respect to the reflected intensity at the fundamental as large as /spl sim/10% are estimated. This suggests that terahertz-sideband generation in semiconductor microcavities is a promising option worthy of exploration for wavelength conversion for wavelength-division multiplexing applications. 相似文献
174.
In this paper, the authors present the results of experiments which clearly demonstrate a technical basis confirming that the carrier frequency harmonics data can be used for diagnostics relative to motor stator insulation degradation. 相似文献
175.
Determination of dislocation densities in HCP metals from X-ray diffraction line-broadening analysis
Griffiths M. Sage D. Holt R. A. Tome C. N. 《Metallurgical and Materials Transactions A》2002,33(13):859-865
X-Ray diffraction (XRD) line-broadening analysis has been performed on highly textured Zr-2.5Nb specimens which had been deformed
in tensile tests to produce well-controlled dislocation structures. An iterative deconvolution method has been applied to
extract the broadening function for the material, using as standards, a Zr single crystal and a 0 pct deformed specimen. In
both cases, for specific tensile tests, a significant contribution to the basal line braodening was observed, which was clearly
not directly related to the dislocation structure generated by the deformation, i.e., so-called c-component dislocations having a component of their Burgers vectors perpendicular to the basal plane. Calculations showed
that the extent of basal line broadening cannot be attributed to the secondary effect of strain from a-type dislocations, i.e., dislocations with Burgers vectors parallel with the basal plane. It is concluded that most of the line broadening observed
was the result of intergranular strain distributions. These distributions are most prominent for grains oriented with their
c-axes perpendicular to the tensile-deformation axis and resulted in basal-plane line broadening even when there were few,
if any, c-component dislocations present.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science and Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
176.
(U,Gd)O2 sintered pellets are fabricated by different methods. The homogeneity characterisation of the Gd content seems to be necessary for a production control to qualify the process and the final product obtained. In this paper, we propose an analysis of the X-ray diffraction powder patterns through the Rietveld method, in which the differences between the experimental and the calculated data proposed from a crystalline structure model are evaluated. This result allows us to determine the cell parameters, that can be correlated with the Gd concentration, and the existence of other phases with different Gd contents. 相似文献
177.
Interface characteristics of carbon fibre reinforced copper matrix composites materials with various interface states and their effect on the flexural strength of composites have been studied. Interfacial states are mechanical bonding, dissolution bonding and reaction bonding. To a certain extent, raising the interfacial strength enables an increase in the flexural strength due to prevention of carbon fibre being pulled out under low stress during fracture process of composites. Raising the interfacial bondage strength, causes the brittleness of composites to increase; the fracture surface of composites is converted from a fibre pull-out model to a fibre even model. While strengthening the interface bondage, the extent of chemical reaction and dissolution at the interface must be controlled to avoid degrading the carbon fibre. 相似文献
178.
It is established that the capillary rise of a liquid has an oscillatory character, in contrast to the commonly accepted opinion that a vertical capillary is filled at a monotonically varying velocity. The value of the tangential shear stress arising in an ascending liquid is evaluated for ethyl alcohol and distilled water. 相似文献
179.
A. D. Pogrebnyak M. V. Il’yashenko V. S. Kshnyakin V. V. Ponaryadov Sh. M. Ruzimov Yu. N. Tyurin 《Technical Physics Letters》2003,29(12):1028-1030
Chromium carbide-nickel coatings were deposited onto a technical grade copper substrate by means of a high-velocity plasma
jet of a plasmatron operating in specially selected regimes. An analysis of the coatings showed evidence of the formation
of a Ni-based solid solution, a complex chromium carbide (Cr7C3), and an fcc crystal phase with a lattice parameter of 3.614 Å. The surface of the coatings exhibits a characteristic relief
resulting from a dynamic interaction between melted and fused particles of the initial powder. The local hardness on some
areas of the surface and in depth of the coating reaches 66±4.5 HRC, while the coating adhesion strength varies from 25 to
300 MPa. 相似文献
180.
Intraseptal scopolamine has differential effects on Pavlovian eye blink and heart rate conditioning.
Evaluated the effects of intraseptal scopolamine hydrobromide (40 μg) injections on Pavlovian (classical) conditioning, with tones used as the CS and a periorbital electric shock train as the UCS, using New Zealand albino rabbits. Eyeblink (EB) and heart rate (HTR) CRs were concomitantly recorded. Although injections of scopolamine into the medial septum impaired the acquisition of the Pavlovian conditioned eyelid reflex, these injections enhanced the magnitude of accompanying Pavlovian conditioned HTR decelerations. However, scopolamine applied to the lateral septal area had no effect on EB conditioning, relative to the vehicle; like medial injections, scopolamine also enhanced the magnitude of the accompanying HTR decelerations. Results are compatible with those of previous investigations indicating that medial septal dysfunction impairs somatomotor conditioning but leaves autonomic conditioning intact and that septal dysfunction produces a parasympathetic bias of the cardiovascular system. (49 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献