全文获取类型
收费全文 | 667篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 99篇 |
金属工艺 | 56篇 |
机械仪表 | 10篇 |
建筑科学 | 8篇 |
能源动力 | 17篇 |
轻工业 | 25篇 |
水利工程 | 1篇 |
石油天然气 | 2篇 |
无线电 | 77篇 |
一般工业技术 | 165篇 |
冶金工业 | 72篇 |
原子能技术 | 53篇 |
自动化技术 | 99篇 |
出版年
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 17篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 19篇 |
2017年 | 21篇 |
2016年 | 21篇 |
2015年 | 11篇 |
2014年 | 21篇 |
2013年 | 29篇 |
2012年 | 40篇 |
2011年 | 28篇 |
2010年 | 39篇 |
2009年 | 39篇 |
2008年 | 35篇 |
2007年 | 21篇 |
2006年 | 30篇 |
2005年 | 15篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 15篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 14篇 |
1998年 | 22篇 |
1997年 | 15篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 15篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1979年 | 7篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1969年 | 3篇 |
1968年 | 3篇 |
排序方式: 共有689条查询结果,搜索用时 601 毫秒
71.
F. Ochoa J. J. Williams N. Chawla 《JOM Journal of the Minerals, Metals and Materials Society》2003,55(6):56-60
The microstructure, tensile, and creep behavior of bulk Sn-3.5Ag solder were studied as a function of cooling rate. Controlled
cooling rates were obtained by cooling specimens in different media: water, air, or furnace. The cooling rate significantly
affected secondary dendrite arm size and spacing of the tin-rich phase, as well as the morphology of Ag3Sn. Ag3Sn was relatively spherical at the fastest cooling rate and had a needle-like morphology at the slowest cooling rate. Both
the yield strength in tension and creep resistance of Sn-3.5Ag solder increased with increasing cooling rate while the strain-to-failure
decreased. In this study, the mechanical behavior was correlated with the observed microstructure, creep-stress exponents,
and fracture behavior, in order to understand the underlying damage mechanisms.
For more information, contact N. Chawla, Arizona State University, Department of Chemical and Materials Engineering, P.O.
Box 876006, Tempe, AZ, 85287-6006; (480) 965-2402; fax (480) 965-0037; e-mail nchawla@asu.edu. 相似文献
72.
To adequately characterize the behavior of solder spheres in electronic packaging, their mechanical behavior needs to be studied
at small-length scales. The creep behavior of single Sn-3.5Ag solder spheres on a copper substrate was studied between 25°C
and 130°C using a microforce testing system. In the low-stress regime, the creep stress exponent changed from 6 at lower temperatures
to 4 at higher temperatures, indicating creep by dislocation climb. The activation energy for creep was also found to be temperature
dependent, and correlated with values for dislocation core diffusion and lattice diffusion in pure tin. A change in the stress
exponent with increasing stress was also observed and explained in terms of a threshold stress for dislocation motion, due
to the presence of obstacles in the form of Ag3Sn particles.
For more information, contact N. Chawla, Arizona State University, Department of Chemical and Materials Engineering, Ira A.
Fulton School of Engineering, Tempe, AZ 85287-6006; e-mail nchawla@asu.edu. 相似文献
73.
The effect of cooling rate on microstructure and creep behavior of bulk, eutectic Sn-3.5Ag solders was studied. The cooling
rate is an important processing variable that significantly affects the microstructure of the solder and therefore determines
its mechanical behavior. Controlled cooling rates were obtained by cooling specimens in different media: water, air, and furnace,
which resulted in cooling rates of 24°C/s, 0.5°C/s, and 0.08°C/s, respectively. The cooling rate decreased the secondary dendrite
arm size and the spacing of the Sn-rich phase, as well as the morphology of Ag3Sn. The Sn-dendrite arm size and spacing were smaller at fast cooling rates, while slower cooling rates yielded a nearly eutectic
microstructure. The morphology of Ag3Sn also changed from relatively spherical, at faster cooling rates, to needlelike for slower cooling. The effect of cooling
rate on creep behavior was studied at 25°C, 60°C, 95°C, and 120°C. Faster cooling rates were found to increase the creep strength
of the solder due to the refinement of the solder microstructure. Stress exponents, n, indicated that dislocation climb was
the controlling mechanism. Activation energies, for all cooling rates, indicated that the dominant diffusional mechanism corresponded
to dislocation pipe diffusion of Sn. Grain boundary sliding (GBS) measurements were conducted, using both scanning electron
microscopy (SEM) and atomic force microscopy (AFM). It was observed that GBS had a very small contribution to the total creep
strain. 相似文献
74.
The tensile behavior and microstructure of bulk, Sn-3.5Ag solders as a function of cooling rate were studied. Cooling rate
is an important processing parameter that affects the microstructure of the solder and, therefore, significantly influences
mechanical behavior. Controlled cooling rates were obtained by cooling specimens in different media: water, air, and furnace.
Cooling rate significantly affected secondary dendrite-arm size and spacing of the Sn-rich phase, as well as the aspect ratio
of Ag3Sn. The Sn-rich dendrite-arm size and spacing were smaller for water-cooled specimens than for air-cooled specimens. Furnace
cooling yielded a nearly eutectic microstructure because the cooling rate approached equilibrium cooling. The morphology of
Ag3Sn also changed from spherical, at a fast cooling rate, to a needlelike morphology for slower cooling. The changes in the
microstructure induced by the cooling rate significantly affected the mechanical behavior of the solder. Yield strength was
found to increase with increasing cooling rate, although ultimate tensile strength and strain-to-failure seemed unaffected
by cooling rate. Cooling rate did not seem to affect Young’s modulus, although a clear coorelation between modulus and porosity
was obtained. The mechanical behavior was correlated with the observed microstructure, and fractographic analysis was employed
to elucidate the underlying damage mechanisms. 相似文献
75.
An analysis of strain in chip breaking using slip-line field theory with adhesion friction at chip/tool interface 总被引:1,自引:0,他引:1
A slip-line field model for orthogonal cutting with step-type chip breaker assuming adhesion friction at chip/tool interface is developed using Kudo's basic slip-line field. An alternative method is suggested for estimation of breaking strain in the chip. The model proposed predicts that with decrease in distance of chip breaker from the cutting edge of the tool, the breaking strain and shear strain in the secondary deformation zone increase while the total plastic strain decreases. The breaking of the chip is found to be solely dependent on the breaking strain, and not on ‘material damage’ or the specific cutting energy. The chip radius of curvature, cutting ratio, range of position of chip breaker for effective chip breaking are computed. The calculated results are found to be in general agreement with experimental measurements. 相似文献
76.
77.
Explosive shock-compression processing is used to fabricate Ti3Al and TiAl composites reinforced with TiB2. The reinforcement ceramic phase is either added as TiB2 particulates or as an elemental mixture of Ti + B or both TiB2 + Ti + B. In the case of fine TiB2 particulates added to TiAl and Ti3Al powders, the shock energy is localized at the fine particles, which undergo extensive plastic deformation thereby assisting in bonding the coarse aluminide powders. With the addition of elemental titanium and boron powder mixtures, the passage of the shock wave triggers an exothermic combustion reaction between titanium and boron. The resulting ceramic-based reaction product provides a chemically compatible binder phase, and the heat generated assists in the consolidation process. In these composites the reinforcement phase has a microhardness value significantly greater than that of the intermetallic matrix. Furthermore, no obvious interface reaction is observed between the intermetallic matrix and the ceramic reinforcement. 相似文献
78.
79.
80.
The NEPTUN test facility is currently being used for reflooding experiments in tight hexagonal geometry, representative of light water high conversion reactors (LWHCRs). Results of parametric studies, based on over sixty forced-feed bottom reflooding experiments carried out with the NEPTUN-III (p / d = 1.13) test bundle, show that flooding rate is the most important, single thermal-hydraulics parameter.Direct comparisons with earlier NEPTUN experiments in standard LWR geometry indicate — on the basis of pressure difference considerations — that much smaller flooding rates may be expected to occur in tight LWHCR cores. The corresponding NEPTUN-III experiments show long-lasting rod surface temperature excursions with relatively high maximum temperatures being reached, and some of the more detailed experimental data collected is used to explain this behaviour. In spite of the above, rewetting of the tight-LWHCR geometry bundle was found to occur in all experiments with reasonably LWHCR-representative values for the various thermal-hydraulics parameters. 相似文献