全文获取类型
收费全文 | 53879篇 |
免费 | 3055篇 |
国内免费 | 157篇 |
专业分类
电工技术 | 780篇 |
综合类 | 73篇 |
化学工业 | 11578篇 |
金属工艺 | 2274篇 |
机械仪表 | 3506篇 |
建筑科学 | 1177篇 |
矿业工程 | 28篇 |
能源动力 | 2275篇 |
轻工业 | 4158篇 |
水利工程 | 276篇 |
石油天然气 | 92篇 |
武器工业 | 2篇 |
无线电 | 8572篇 |
一般工业技术 | 11671篇 |
冶金工业 | 4346篇 |
原子能技术 | 730篇 |
自动化技术 | 5553篇 |
出版年
2024年 | 27篇 |
2023年 | 569篇 |
2022年 | 727篇 |
2021年 | 1560篇 |
2020年 | 1145篇 |
2019年 | 1282篇 |
2018年 | 1543篇 |
2017年 | 1529篇 |
2016年 | 1908篇 |
2015年 | 1412篇 |
2014年 | 2276篇 |
2013年 | 3318篇 |
2012年 | 3555篇 |
2011年 | 4253篇 |
2010年 | 3059篇 |
2009年 | 3206篇 |
2008年 | 3045篇 |
2007年 | 2378篇 |
2006年 | 2209篇 |
2005年 | 1886篇 |
2004年 | 1717篇 |
2003年 | 1666篇 |
2002年 | 1471篇 |
2001年 | 1230篇 |
2000年 | 1116篇 |
1999年 | 1040篇 |
1998年 | 1720篇 |
1997年 | 1140篇 |
1996年 | 911篇 |
1995年 | 628篇 |
1994年 | 511篇 |
1993年 | 477篇 |
1992年 | 337篇 |
1991年 | 327篇 |
1990年 | 290篇 |
1989年 | 258篇 |
1988年 | 229篇 |
1987年 | 178篇 |
1986年 | 132篇 |
1985年 | 144篇 |
1984年 | 107篇 |
1983年 | 73篇 |
1982年 | 45篇 |
1981年 | 51篇 |
1980年 | 46篇 |
1979年 | 44篇 |
1978年 | 36篇 |
1977年 | 48篇 |
1976年 | 75篇 |
1975年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
951.
Functionally graded materials (FGMs) belong to a relatively new class of inhomogeneous composite materials, in which the composition
and/or microstructure undergo a gradual change along some directions. In this review article, the microstructures and composition
gradients in Al/SiC, Al/Shirasu (volcanic eruptions commonly found in south Kyushu in Japan), Al/Al3Ti, Al/Al3Ni, Al/Al2Cu FGMs have been investigated. The Al/SiC, Al/Shirasu and Al/Al3Ti FGMs are fabricated by the centrifugal solid particle method where the distribution particles of SiC, Shirasu and Al3Ti are solids in the melts. On the other hand, Al/Al3Ni and Al/Al2Cu FGMs are fabricated by the centrifugalin-situ method where Al/Al3Ni and Al/Al2Cu systems have lower liquidus temperatures than the processing temperatures. The feature of Al/(Al3Ti−Al3Ni) hydrid FGM, which is fabricated by a method combining both the centrifugal solid-particle andin-situ methods, is also shown. 相似文献
952.
Jooho Hwang Chun-Hong Park Chan-Hong Lee Seung-Woo Kim 《International Journal of Machine Tools and Manufacture》2006,46(7-8):801-810
This paper describes an estimation and correction method for the two-dimensional (2D) position errors of a planar XY stage that is driven along the Y-axis by two linear motors. The 2D position errors of the stage were estimated and corrected based on measured motion errors from a conventional laser interferometer system. To compensate for the planar XY stage 2D position errors, corrections were introduced for the yaw, perpendicular, straightness and 1D position errors along each axis, which are predominantly caused by linear scale, yaw, and pitching motion errors. The effect of the motion error corrections was evaluated by diagonal measurements based on the ISO230-6 standard and six different 1D position error measurements along the X and Y-axes. By applying error motion corrections, the diagonal systematic deviation at the center point was improved from 499.7 μm to 1.16 μm, and the estimated maximum 2D position errors were improved to −0.263 and 0.530 μm in the X and Y directions, respectively. The diagonal systematic deviation at a corner point was 1.23 μm and the estimated maximum difference between the corner and center points improved from −2.603 and 2.603 μm to −0.05 and 0.12 μm in the X and Y directions respectively. 相似文献
953.
Thermoelectric properties of mechanically alloyed iron disilicides consolidated by various processes
Mn doped p-type iron disilicide powders have been produced by a mechanical alloying process. As-milled powders were of metastable
state and mostly transformed to β-FeSi2 phase by subsequent isothermal annealing. As-milled powders were consolidated by various processes such as sintering of the
cold compact in vacuum, vacuum hot pressing (VHP), and spray drying/atmospheric plasma thermal spraying. Phase transitions
during the processes were investigated using XRD, EDS, and SEM. As-consolidated specimens consisted of a mixture of α-Fe2Si5 and ε-FeSi phases, which were gradually transformed into a thermoelectric semiconducting α-FeSi2 phase by subsequent isothermal annealing in the vicinity of 845°C in vacuum. However, some residual α and ε phases remained
even after prolonged annealing. Thermoelectric properties were measured as a function of temperature and correlated with phase
transformation. They showed optimum values in the vacuum hot pressed specimen due to a higher fraction of β phase and/or higher
density. 相似文献
954.
The corrosion behavior of Cr-N coated steels with different phases (-Cr, CrN and Cr2N) deposited by cathodic arc deposition on AISI H13 steel was investigated in a 3.5% NaCl solution at ambient temperature. Potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were the techniques applied to characterize the corrosion behavior. It was found that the CrN coating had a lower current density from potentiodynamic polarization tests than others. The porosity, corresponding to the ratio of the polarization resistance of the uncoated and the coated substrate, was higher in the Cr2N coating than in the other Cr-N coated steels. EIS measurements showed, for most of the Cr-N coated steels, that the Bode plot presented two time constants. Also, the Cr2N coating represented the characteristic of Warburg behavior after 72 h of immersion. The coating morphologies were examined in planar view and cross-section by SEM analysis and the results were compared with those of the electrochemical measurement. The CrN coating had a dense, columnar grain-sized microstructure with minor intergranular porosity. From the above results, it is concluded that the CrN coating provided a better corrosion protection than the other Cr-N coated steels. 相似文献
955.
Design of Bulk metallic glasses with high glass forming ability and enhancement of plasticity in metallic glass matrix composites: A review 总被引:1,自引:0,他引:1
To overcome some of the limits of existing metallic alloys, a new alloy design concept has been introduced recently in order
to control the crystallinity, i.e. to utilize crystalline, quasicrystalline, and amorphous structures. In particular, bulk
metallic glasses (BMGs) receive great attention because of their unique properties due to their different atomic configuration.
Recently, significant progress in enhancing glass forming ability (GFA) has led to the fabrication of BMGs having potential
for application as structural and functional materials. Moreover, successful design of BMG matrix composite microstructure
suggests that the plasticity of BMGs can be controlled properly. In this review article, we introduce recent research results
on the design of BMGs with high GFA and on the enhancement of plasticity in metallic glass matrix composites. 相似文献
956.
A composite coating of aluminide-yttrium has shown excellent corrosion resistance in a cyclic high-temperature hot-corrosion environment. To understand the effect of yttrium on the stability of the composite coating, the specimens were prepared with various coating parameters of Y thickness, sequence of post heat treatment and surface condition before Y-ion plating. Performance of the composite coating was evaluated by isothermal oxidation and cyclic high-temperature hot corrosion. Isothermal-oxidation-test results show that the Y in the composite coating helps to form a thick and dense Al2O3 scale which is ductile and resistant to thermal stress. The Y in Al2O3 may act as a donor which leads to an increase in concentration of interstitial oxygen and, thus, increases in oxidation rate. The presence of Y2O3 and (Y, Al) O-type compounds in grain boundaries of Al2O3 and boundaries between the Al2O3 and NiAl effectively prohibits the fast diffusion of oxidants (such as O and S) and Al along grain boundaries. Consequently, it may induce slow diffusion through the matrix, and thus the corrosion resistance of the composite coating under cyclic hot corrosion increases substantially. 相似文献
957.
Ahn Kyu-Hong Hwang Jong-Hyuk Song Kyung-Guen Jung Yong-Ho Cho Eul-Saeng Lim Byung-Ran Kim Kwang-Soo 《Metals and Materials International》2004,10(2):167-170
The performance of an attached growth wastewater treatment process was investigated in an effort to improve nitrogen removal
efficiency. Recycled Yakult (lactic acid fermentation drink) bottles made of polystyrene were used as a biofilm media. The
use of Yakult bottles as a biofilm media has been attempted by numerous researchers in Japan for the removal of solids and
organics. However, these studies focused only on the removal of solids and organics. This study extended their application
to the removal of nitrogen for domestic sewage treatment. Yakult media was placed in a reactor with 70% apparent reactor volume
in a conventional A/O process. The bottom of the Yakult media was removed, and randomly filled Yakult media were effectively
able to reduce the flow in tanks, resulting in an increase in the contact time between pollutants and microorganisms. With
higher HRT, the nitrogen removal efficiency was increased by up to 83% with 12 hr of HRT. Nitrification appeared to be the
limiting factor of nitrogen removal at an HRT that is less than 12 hr, indicating that the Yakult process requires more retention
time to achieve nitrification compared to other biofilm processes. The removal efficiencies of organics and solids were high
regardless of the change of operational parameters.
This article is based on a presentation in “The 7th Korea-China Workshop On Advanced Materials” organized by the Korea-China
Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju
Hotel, Jeju Island, Korea on August 24–27, 2003. 相似文献
958.
The stability of lamellar structure is crucial for the creep resistance of TiAl alloys, but degradation of the lamellar structure
is unavoidable at high temperatures. The degradation of the lamellar structure in PST crystals of Ti-48mol.%Al was studied
during high temperature exposure (annealing and creep testing) to examine how to make a stable lamellar structure with high
creep deformation resistance. Since the six orientation variants of γ lamellae are nucleated independently of the adjoining
lamellae, pseudo twin and 120° rotational fault boundaries are most frequently observed at the initial stage of lamellar formation.
The preferential removal of high energy (pseudo twin and 120° rotational fault) boundaries during the evolution of lamellar
structure results in the highly probable appearance of a true twin boundary at a later stage of lamellar evolution. The coarsening
of lamellar spacing and the spheroidization of the lamellae are the major degradation events occurring during creep deformation,
and the migration of the lamellar boundaries brings both of them about. The lamellar structures of TiAl alloy contain four
types of lamellar boundaries. The stability of the four types of boundaries decreases in the following order: γ/α2 > true twin > pseudo twin > or=120° rotational fault boundaries. The γ/α2 boundary has the highest stability (lowest mobility), and the high density of γ/α2 boundaries is proposed to make a stable lamellar structure with good creep resistance. A material having the high density
of γ/α2 boundaries was produced through the heat treatment of a PST crystal in the α+γ two-phase regime. The excellent creep properties
of the material were proven through creep tests of hard oriented PST crystals made of the material.
This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials,”
organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei
University, Seoul, Korea on October 25–26, 2002. 相似文献
959.
960.
A coating consisting of (Cr2N−Mo2S3) overlay coating and an underlying Cr coating was deposited on a steel substrate by D.C. magnetron sputtering. The oxidation
characteristics of the deposited double-layered coating were studied at temperatures ranging from 400 to 900 °C in air. The
oxidation product was primarily Cr2O3. The unreacted coating beneath the oxide scale had some dissolved oxygen, sulfur, and iron. Oxidation of the coating occurred
via complex routes such as the outward diffusion of chromium and nitrogen from Cr2N and iron from the substrate, and the inward transport of oxygen from air, chromium from Cr2N, and S from Mo2S3. This counter diffusion of various ions occurred easily via fine crystallites that constituted the coating, which had some
solubility of S, O, and Fe. 相似文献