全文获取类型
收费全文 | 260499篇 |
免费 | 2206篇 |
国内免费 | 319篇 |
专业分类
电工技术 | 4280篇 |
综合类 | 107篇 |
化学工业 | 42376篇 |
金属工艺 | 15478篇 |
机械仪表 | 10359篇 |
建筑科学 | 4376篇 |
矿业工程 | 3825篇 |
能源动力 | 4520篇 |
轻工业 | 10815篇 |
水利工程 | 4240篇 |
石油天然气 | 13074篇 |
武器工业 | 28篇 |
无线电 | 21691篇 |
一般工业技术 | 65235篇 |
冶金工业 | 33566篇 |
原子能技术 | 11313篇 |
自动化技术 | 17741篇 |
出版年
2021年 | 3245篇 |
2019年 | 3125篇 |
2018年 | 5953篇 |
2017年 | 6194篇 |
2016年 | 6491篇 |
2015年 | 3306篇 |
2014年 | 5736篇 |
2013年 | 10877篇 |
2012年 | 7769篇 |
2011年 | 9557篇 |
2010年 | 7796篇 |
2009年 | 8583篇 |
2008年 | 8603篇 |
2007年 | 8202篇 |
2006年 | 6640篇 |
2005年 | 5792篇 |
2004年 | 5692篇 |
2003年 | 5495篇 |
2002年 | 5286篇 |
2001年 | 5073篇 |
2000年 | 5061篇 |
1999年 | 4392篇 |
1998年 | 7494篇 |
1997年 | 6048篇 |
1996年 | 4654篇 |
1995年 | 3849篇 |
1994年 | 3582篇 |
1993年 | 3766篇 |
1992年 | 3335篇 |
1991年 | 3495篇 |
1990年 | 3579篇 |
1989年 | 3466篇 |
1988年 | 3376篇 |
1987年 | 3362篇 |
1986年 | 3240篇 |
1985年 | 3422篇 |
1984年 | 3336篇 |
1983年 | 3238篇 |
1982年 | 3078篇 |
1981年 | 3125篇 |
1980年 | 3142篇 |
1979年 | 3302篇 |
1978年 | 3527篇 |
1977年 | 3511篇 |
1976年 | 3980篇 |
1975年 | 3239篇 |
1974年 | 3321篇 |
1973年 | 3369篇 |
1972年 | 3005篇 |
1971年 | 2767篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The field evaporation of carbidized tungsten (ribbed crystals) was studied by the atom probe method at various temperatures of the sample in the regions of cryogenic, room, and elevated (1300–1600 K) temperatures. For a high pulsed (not less than 40%) component in the evaporating field, the room-temperature field evaporation mass spectra correctly reflect the surface composition of the evaporated sample. The mass spectra reveal a large number of molecular and polymerized (cluster) ions. Data from field ion desorption microscopy indicate that high-temperature field evaporation of a ribbed crystal proceeds via ion emission from walking and merging thermal-field microroughnesses. 相似文献
992.
By combining the methods of boundary integral equations and small parameter, we solve a three-dimensional problem of low-frequency harmonic loading of the surfaces of a shallow crack in an infinite elastic body. The functions of crack opening displacements and the stress intensity factors are obtained in the form of double convergent power series in the wave number and in a geometric parameter characterizing the curvature of the crack. We study the influence of inertial terms on the level of stresses in the vicinity of spheroidal cracks with various values of eccentricity under the action of uniform dynamic pressure with constant amplitude. 相似文献
993.
Borodina I. A. Zaitsev B. D. Kuznetsova I. E. Teplykh A. A. Shurygin V. V. 《Technical Physics Letters》2003,29(9):781-783
The conditions for hybridization of the zero-order and high-order acoustic waves propagating in a piezoelectric crystal plate have been studied. The dependence of the phase velocity of the hybrid waves on the parameter hf (h is the plate thickness and f is the wave frequency) is established for the potassium niobate and lithium niobate plates possessing various crystallographic orientations and conductivities. It is found that hybridization takes place when the conductivity of a thin surface layer exceeds a certain critical value, which can vary within broad limits depending on the plate material and orientation. The degree of dispersive repulsion of the coupled modes grows with increasing electromechanical coupling coefficient. 相似文献
994.
On the example of KS25 and KS37 samarium–cobalt-base commercial alloys and LaNi4.5Al0.5 alloy, we show the possibility, in principle, of obtaining functional materials in the nanocrystalline state with the help of a planetary mill in hydrogen medium. Milling with a rotational speed of 600 rpm during 24 h leads to the disproportionation of KS25 and KS37 alloys into samarium hydride and iron–cobalt (cobalt) and of LaNi4.5Al0.5 into Ni3Al and amorphous products. After vacuum annealing up to 1181 K, the main phases of samarium–cobalt materials are recombined. The crystallite sizes after annealing are 58–72 and 70 nm for KS25 and KS37, respectively. We established that LaNi4.5Al0.5 alloy is not recombined in vacuum, and the nanocrystalline state in it can be reached by milling up to 30 min. The crystallite sizes constitute 45–78 nm. 相似文献
995.
996.
S. V. Prikhodko Y. Ma A. J. Ardell D. G. Isaak J. D. Carnes S. Moser 《Metallurgical and Materials Transactions A》2003,34(9):1863-1868
The adiabatic elastic stiffness constants C
ij of Ni-Si single-crystal solid-solution alloys of two slightly different compositions, 10.78 and 11.17 at. pct Si, were measured
over the temperature range from 20 °C to 900 °C using the rectangular parallelepiped resonance method. The isotropic elastic
constants of the polycrystalline ordered intermetallic compound Ni3Si containing 23 at. pct Si were also measured over this temperature range. Values of the C
ij for Ni3Si were estimated from the data on the polycrystalline alloy, as well as from published data in the literature on isomorphous
ternary ordered intermetallic compounds containing different amounts of Si. Using measured values and previously published
data, the stiffness constants of Ni3Ti were estimated; these are the only available data on this alloy. The estimated single-crystal elastic constants of Ni3Si, as well as the experimentally measured bulk modulus, are considerably smaller than published values calculated from first-principles
methods. The same is true for the C
ij of Ni3Ti, but the discrepancies are smaller. 相似文献
997.
Thin-film nickel coatings on fiber materials 总被引:1,自引:0,他引:1
L. M. Lyn’kov V. A. Bogush E. A. Senkovets S. M. Zavadskii 《Technical Physics Letters》2003,29(8):641-642
Vacuum deposition of thin films onto fiber materials is a promising method of obtaining electromagnetic screens. We have studied the structure and the electromagnetic properties of machine-knitted fabric coated with nickel by means of magnetron sputtering. When the fabric is irradiated from the metal-coated side, the reflection coefficient is higher by a factor of 1.4 as compared to the case when the same source of electromagnetic radiation is situated on the opposite side (facing the uncoated surface), while the absorption coefficient in both cases is the same. 相似文献
998.
The fabrication and characterization of two‐photon polymerized features written within and outside of colloidal crystals is presented. Two‐photon polymerization (TPP) response diagrams are introduced and developed to map the polymerization and damage thresholds for features written via modulated beam rastering. The use of tris[4‐(7‐benzothiazol‐2‐yl‐9,9‐diethylfluoren‐2‐yl)phenyl]amine (AF‐350) as an initiator for TPP is demonstrated for the first time and TPP response diagrams illustrate the polymerization window. These diagrams also demonstrate that the polymerization behavior within and outside of colloidal crystals is similar and electron microscopy reveals nearly identical resolution. Fluorescence confocal microscopy further enables visualization of non‐self‐supporting, three‐dimensional TPP features within self‐assembled photonic crystals. Finally, microspot spectroscopy is collected from a two‐photon feature written within a colloidal crystal and this is compared with simulation. 相似文献
999.
The corrosion behaviour of nitrogen-containing austenitic stainless steel in methanol containing different concentrations
of H2SO4, HCl, LiCl and H2SO4 + HCl has been investigated using a potentiostatic polarization method. The cathodic reaction in the H2SO4, HCl and H2SO4 + HCl solutions was proton reduction whereas in the neutral LiCl solution, oxygen reduction was the predominant cathodic
reaction. Active, passive and transpassive behaviours were observed only for higher concentrations of H2SO4 (0.01–2.0 M) due to the inherent water content. A cathodic loop, characterized by measured negative current in the anodic
region, was also observed in solutions, in which the concentration of H2SO4 was 1.0 M or higher. The relative stability of the passive films decreased as the H2SO4 concentration increased, and thus the steel suffered from mild pitting corrosion. In the chloride environment, the rate of
corrosion increased as the Cl− ion concentration increased. The presence of acid along with Cl− ions enhanced corrosion, and the corrosion rate increased significantly. The steel suffered from mild intergranular corrosion
in acidic chloride solutions of methanol. In the H2SO4 + HCl solutions, passive films were only formed when the H2SO4 to HCl concentration ratio was greater than ∼10:1. 相似文献
1000.