全文获取类型
收费全文 | 54227篇 |
免费 | 2993篇 |
国内免费 | 169篇 |
专业分类
电工技术 | 790篇 |
综合类 | 70篇 |
化学工业 | 11699篇 |
金属工艺 | 2295篇 |
机械仪表 | 3484篇 |
建筑科学 | 1211篇 |
矿业工程 | 49篇 |
能源动力 | 2300篇 |
轻工业 | 4215篇 |
水利工程 | 298篇 |
石油天然气 | 98篇 |
武器工业 | 2篇 |
无线电 | 8647篇 |
一般工业技术 | 11609篇 |
冶金工业 | 4239篇 |
原子能技术 | 712篇 |
自动化技术 | 5671篇 |
出版年
2024年 | 54篇 |
2023年 | 617篇 |
2022年 | 959篇 |
2021年 | 1594篇 |
2020年 | 1159篇 |
2019年 | 1289篇 |
2018年 | 1555篇 |
2017年 | 1533篇 |
2016年 | 1916篇 |
2015年 | 1407篇 |
2014年 | 2272篇 |
2013年 | 3319篇 |
2012年 | 3561篇 |
2011年 | 4287篇 |
2010年 | 3054篇 |
2009年 | 3244篇 |
2008年 | 3054篇 |
2007年 | 2392篇 |
2006年 | 2224篇 |
2005年 | 1906篇 |
2004年 | 1726篇 |
2003年 | 1677篇 |
2002年 | 1469篇 |
2001年 | 1228篇 |
2000年 | 1096篇 |
1999年 | 1025篇 |
1998年 | 1681篇 |
1997年 | 1091篇 |
1996年 | 877篇 |
1995年 | 612篇 |
1994年 | 515篇 |
1993年 | 460篇 |
1992年 | 335篇 |
1991年 | 311篇 |
1990年 | 286篇 |
1989年 | 260篇 |
1988年 | 220篇 |
1987年 | 186篇 |
1986年 | 132篇 |
1985年 | 146篇 |
1984年 | 109篇 |
1983年 | 68篇 |
1982年 | 43篇 |
1981年 | 46篇 |
1980年 | 44篇 |
1979年 | 43篇 |
1978年 | 34篇 |
1977年 | 45篇 |
1976年 | 67篇 |
1975年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
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
962.
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
963.
964.
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
965.
Chan-Yeol Seo Seung-Jun Choi Jeon Choi Choong-Nyeon Park Paul. S. Lee Jai-Young Lee 《Journal of Alloys and Compounds》2003,350(1-2):324-331
AB5-type intermetallic compounds were prepared by arc-melting in argon atmosphere. The composition of a stoichiometric compound LaNi3.6Al0.4Co0.7Mn0.3 with a hexagonal CaCu5 structure was varied by stoichiometric and nonstoichiometric addition of Ti. With the increase of the Ti y0.05 content in LaNi3.6Al0.4Co0.7Mn0.3Tiy, the hydrogen storage capacity is enhanced, whereas when y=0.1–0.3, it is decreased. The discharge capacity and cyclability are increased considerably by addition of titanium in the range of 0.02–0.1 with a maximum value at about 0.1%. The highest maximum capacity is achieved for a nonstoichiometric addition of 0.05% Ti. The kinetic properties are also additionally improved by the formation of a titanium-rich second phase. This can explain the improvement of the capacity for alloys with low Ti content. The decrease in capacity for high Ti content was also correlated with the amount of the Ti-rich phase. Therefore, the improvement of kinetics are due to the catalytic effect, grain boundary diffusion effect or more pronounced alloy pulverization upon cycling. This study has been aimed to improve the electrode properties of a series of multicomponent LaNi3.6Al0.4Co0.7Mn0.3Tiy (y=0.0, 0.02, 0.05, 0.1, 0.2, 0.3) alloys which have mutual complementary properties. All the prepared alloys have been subjected to analyses by EDS, SEM and XRD. In order to determine the hydrogen storage capacity, the pressure composition isotherms (P–C–T curves) have been used. The metal hydride electrodes were characterized by galvanostatic cycling test. 相似文献
966.
The relationship between the yield ratio and the material constants,b andN, of the Swift equation for hotrolled low carbon steels has been established. The yield ratio calculated by using the Swift
equation agrees well with an experimentally obtained yield ratio. It was found that the yield ratio decreases with an increasing
value ofN or with a decreasing value ofb. It was also found, however, that high yield strength is associated with small values of bothb andN. Therefore, to obtain both high yield strength and low yield ratio, a detailed microstructural control is needed to determine
the optimum values ofb andN. 相似文献
967.
Hyoun Woo Kim Kwang-sik Kim Woon-suk Hwang Rafael Reif 《Metals and Materials International》2002,8(5):463-467
We investigated the effect of the rinsing and drying technique on the oxygen and carbon concentration on a silicon surface.
Rinsing in deionized water increased the interfacial oxygen concentration and helped generate defects. Blow-drying was more
efficient than spin-drying in reducing interfacial oxygen concentration. Exposure to the atmosphere was detrimental to obtaining
high crystallinity in the epitaxial layer. We evaluated the effectiveness of the cleaning process by observing the grown epilayer
and the epilayer/substrate interface. 相似文献
968.
Kyu-Seog Hwang Chi-Kyoon Kim Sang-Bok Kim Jeong-Tae Kwon Joo-Sang Lee Yeon-Hum Yun Yun-Ho Kim Bo-An Kang 《Surface & coatings technology》2002,150(2-3):177-181
Epitaxial and polycrystalline Bi4Ti3O12 thin films were prepared on single crystal (100) MgO substrates by a chemical solution deposition process using metal naphthenates as starting materials. Pyrolyzed films (at 500°C) were annealed for 30 min in air at 650, 700, 750 and 800°C, respectively. The effects of annealing temperature on the crystallinity, epitaxy and surface morphology of the films were investigated by X-ray diffraction θ-2θ scans, pole-figure analysis, and atomic force microscopy (AFM). Epitaxially grown films annealed at 700 and 750°C, respectively, showed growth of three-dimensional needle-shaped grains. During annealing at 800°C, grain growth of Bi4Ti3O12 may be suppressed by the formation of a titanium-rich phase such as Bi2Ti2O7 owing to Bi volatilization, resulting in lower root mean square roughness than that of film annealed at 750°C. 相似文献
969.
To investigate the effects of introducing the iron compound on the carbonization behavior polyacrylonitile (PAN)-based electrospun nanofibers were carbonized with or without iron(III) acetylacetonate (AAI) over the temperature range of 900–1500 °C in nitrogen atmosphere. The morphological characteristics of the carbon nanofibers were investigated using X-ray diffractometer (XRD), Raman spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The electrical conductivity of the carbon nanofiber web was measured by four-point probe method. The iron catalyst had a profound effect on the crystal structure of the carbonized nanofiber. In the presence of AAI the nanofibers carbonized at 1300 °C developed graphite structure, which could be obtained at the temperature higher than 2000 °C in the absence of the catalyst. The in-plane size of the graphite crystals (La) was measured to be about 6.5 nm by Raman spectroscopy and the (0 0 2) spacing by XRD was 0.341 nm. 相似文献
970.
Superplastic deformation and crystallization behavior of a Cu54Ni6Zr22Ti18 metallic glass were investigated. A maximum elongation of 650% was obtained at 733 K at 1 × 10−2 s−1 from the sheet fabricated by squeeze copper-mold casting method. At low strain rates, the strain-rate-sensitivity exponent value was close to 1, suggesting that Newtonian-like behavior governed the plastic flow. At a high strain rate around 10−2 s−1, a transition from Newtonian to non-Newtonian behavior took place with decrease in m value. Large strain hardening by crystallization occurred during the course of deformation. The strain hardening was found to be caused by crystallization according to the analyses of the relation of true stress vs. testing time, T-T-T diagram and DSC characteristics. The time periods up to the strain before strain hardening at 733 K for the Cu54Ni6Zr22Ti18 metallic glass were similar to that of the Zr65Al10Ni10Cu15 metallic glass at 696 K as 180–300 s (3–5 min). This coincidence could be explained by comparison of their T-T-T diagrams showing that the incubation times for crystallization of the Cu BMG at 733 K and for Zr BMG at 696 K are similar. 相似文献