全文获取类型
收费全文 | 2685篇 |
免费 | 49篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 44篇 |
综合类 | 3篇 |
化学工业 | 447篇 |
金属工艺 | 78篇 |
机械仪表 | 53篇 |
建筑科学 | 144篇 |
矿业工程 | 10篇 |
能源动力 | 51篇 |
轻工业 | 173篇 |
水利工程 | 24篇 |
石油天然气 | 14篇 |
无线电 | 200篇 |
一般工业技术 | 389篇 |
冶金工业 | 673篇 |
原子能技术 | 22篇 |
自动化技术 | 413篇 |
出版年
2022年 | 23篇 |
2021年 | 23篇 |
2020年 | 20篇 |
2019年 | 26篇 |
2018年 | 33篇 |
2017年 | 33篇 |
2016年 | 39篇 |
2015年 | 35篇 |
2014年 | 55篇 |
2013年 | 152篇 |
2012年 | 78篇 |
2011年 | 114篇 |
2010年 | 75篇 |
2009年 | 75篇 |
2008年 | 135篇 |
2007年 | 94篇 |
2006年 | 90篇 |
2005年 | 85篇 |
2004年 | 82篇 |
2003年 | 76篇 |
2002年 | 79篇 |
2001年 | 49篇 |
2000年 | 49篇 |
1999年 | 53篇 |
1998年 | 75篇 |
1997年 | 38篇 |
1996年 | 51篇 |
1995年 | 43篇 |
1994年 | 62篇 |
1993年 | 36篇 |
1992年 | 54篇 |
1991年 | 32篇 |
1990年 | 43篇 |
1989年 | 37篇 |
1988年 | 36篇 |
1987年 | 33篇 |
1986年 | 33篇 |
1985年 | 37篇 |
1984年 | 45篇 |
1983年 | 42篇 |
1982年 | 41篇 |
1981年 | 31篇 |
1980年 | 32篇 |
1979年 | 27篇 |
1978年 | 33篇 |
1977年 | 30篇 |
1976年 | 34篇 |
1975年 | 23篇 |
1974年 | 29篇 |
1973年 | 27篇 |
排序方式: 共有2738条查询结果,搜索用时 0 毫秒
1.
W. Chen S. -H. Wang R. Chu F. King T. R. Jack R. R. Fessler 《Metallurgical and Materials Transactions A》2003,34(11):2601-2608
A study was carried out to understand the effect of precyclic loading on stress-corrosion-crack initiation in an X-65 pipeline
steel exposed to a near-neutral-pH soil environment. The test specimens were precyclically loaded before corrosion exposure
to represent a service history of up to about 20 years, depending on the severity of pressure fluctuation. Microcracks had
initiated on the polished surface of the X-65 pipeline steel after long-time exposure at open-circuit potential (OCP) in a
near-neutral-pH synthetic soil solution. These microcracks were mostly initiated from pits at metallurgical discontinuities
such as grain boundaries, pearlitic colonies, and banded phases in the steel. Strong preferential dissolution was observed
along planes of the banded structures in the steel. The selective corrosion attack at these metallurgical discontinuities
is attributed to the galvanic nature of those areas to their neighbors. Cyclic loading prior to corrosion exposure had significant
effects on microcrack initiation and propagation during subsequent corrosion exposure. Cyclic loading prior to corrosion exposure
either reduced or increased the probability of crack initiation and the rate of crack propagation, depending upon the magnitude
of the stress cycles. The largest reduction was seen at a peak cyclic stress of about 0.8 of the yield strength. This cyclic-loading-dependent
cracking behavior might be related to the alteration of the substructures and the residual stress in the steel as a result
of precyclic loading. 相似文献
2.
3.
The role of gas phase CH3 radicals in the oxidative coupling of CH4 over 1 wt% Sr/La2O3 is supported by the observations that (i) this is a very effective catalyst for the generation of CH3 · radicals and (ii) the concentration of CH3 · radicals increases with temperature over the range of 450 °C–800 °C. 相似文献
4.
Jack E. Snell 《Fire Technology》1994,30(3):357-365
The FORUM for International Cooperation on Fire Research is an informal group of people committed to fire research and the application of fire-research results. Since it was formed in 1988, the FORUM has brought together organizational leaders who direct resources for fire research throughout the world. This article is reprinted from the Nordic Fire Safety Engineering Symposium, Development and Verification of Tools for Performance Codes, August 30–September 1, 1993, in Espoo, Finland. 相似文献
5.
Jack F. Douglas 《Computational Materials Science》1995,4(4):292-308
Although some patterns of physical behavior are common in the glass transition and in the properties of supercooled liquids and glasses (characteristic viscoelasticity, temperature dependence of viscosity and relaxation times, property evolution through “physical aging”, difficulties in performing equilibrium measurements or simulations, etc.), it is difficult to arrive at a definition of the glass transition which distinguishes it from other phenomena exhibiting similar features. The present paper addresses this problem by defining a dynamical measure of order involving the average “shape” of particle trajectories in supercooled liquids. This dynamic order parameter should provide a measure of “closeness” to the glass transition and some indirect insights into the physical nature of supercooled liquids and glasses. Arguments are given that the proposed dynamic measure of order [“generalized capacity”, C(T)] is related to the temperature-dependent “effective hydrodynamic radius” RH(T) measured in supercooled liquids and model numerical calculations are given to support this view. Some consequences of the intermittent particle motion at low temperatures for stress relaxation are also discussed. 相似文献
6.
Abstract. A vector time series model of the form A(L)y(t) + B(L)x(t) =ε(t) is known as a vector autoregressive model with exogenous variables (VARX model) and involves a regressand vector y(t) and a regressor vector x(t). This paper provides a method for the recursive fitting of subset VARX models. It suggests the use of ascending recursions in conjunction with an order selection criterion to choose an 'optimum' subset VARX model. 相似文献
7.
Tung oil 总被引:2,自引:0,他引:2
Jack Greenfield 《Journal of the American Oil Chemists' Society》1959,36(11):565-574
8.
Petroleum pitch (Ashland A240) has been subjected to thermal treatment and solvent fractionation to produce refined pitches to be evaluated as impregnants for C-C composites. The solvent fractions were obtained by sequential Soxhlet extraction with solvents such as hexane, benzene, and pyridine. Thermal treatment to 408 °C produced a mesophase pitch (≈50% mesophase); an appreciable portion of the mesophase was soluble in strong solvents. There were substantial differences in chemical composition and in pyrolysis behaviour of the fractions. As the depth of fraction increased, the pyrolysis yield and bloating increased, and the microstructure of the coke became finer until glassy microconstituents were formed in the deepest fractions. 相似文献
9.
The interfacial reaction between styrene/maleic anhydride copolymer (SMA) and amine-terminated butadiene-acrylonitrile copolymer (ATBA) was observed using Fourier transform infrared (FTIR) imaging spectroscopy. The anhydride and amine reacted to form an imide. Each component was detected using a characteristic wavenumber, which was 1601 cm -1 for SMA, 2237 cm -1 for ATBA, and 1701 cm -1 for the imide. FTIR images were taken as the reaction proceeded at 150, 160, 170, and 180°C. At low temperatures (150 and 160°C), diffusion-controlled kinetics were observed since interdiffusion between the reactants did not appear in the images. On the other hand, both the diffusion front and the reaction front are observed in the images at high reaction temperatures (170 and 180°C), which indicates that the kinetics became reaction-controlled rather than diffusion-controlled. Absorbance profiles were extracted from the images and used for the calculation of the extent of reaction. The data were analyzed using the Frederickson and Milner theory based on the assumption of diffusion-controlled kinetics, and this theory fit the low reaction temperature data. 相似文献
10.
Iris Reinbacher Marc Benkert Marc van Kreveld Joseph S. B. Mitchell Jack Snoeyink Alexander Wolff 《Algorithmica》2008,50(3):386-414
In geographic information retrieval, queries often name geographic regions that do not have a well-defined boundary, such
as “Southern France.” We provide two algorithmic approaches to the problem of computing reasonable boundaries of such regions
based on data points that have evidence indicating that they lie either inside or outside the region. Our problem formulation
leads to a number of subproblems related to red-blue point separation and minimum-perimeter polygons, many of which we solve
algorithmically. We give experimental results from our implementation and a comparison of the two approaches.
This research is supported by the EU-IST Project No. IST-2001-35047 (SPIRIT) and by grant WO 758/4-2 of the German Research
Foundation (DFG). 相似文献