全文获取类型
收费全文 | 365篇 |
免费 | 48篇 |
国内免费 | 57篇 |
专业分类
化学 | 101篇 |
晶体学 | 5篇 |
力学 | 136篇 |
综合类 | 14篇 |
数学 | 20篇 |
物理学 | 194篇 |
出版年
2023年 | 5篇 |
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 20篇 |
2019年 | 8篇 |
2018年 | 4篇 |
2017年 | 17篇 |
2016年 | 17篇 |
2015年 | 17篇 |
2014年 | 22篇 |
2013年 | 30篇 |
2012年 | 24篇 |
2011年 | 19篇 |
2010年 | 15篇 |
2009年 | 15篇 |
2008年 | 15篇 |
2007年 | 13篇 |
2006年 | 18篇 |
2005年 | 13篇 |
2004年 | 27篇 |
2003年 | 20篇 |
2002年 | 8篇 |
2001年 | 22篇 |
2000年 | 15篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有470条查询结果,搜索用时 15 毫秒
101.
Hydro-mechanical aspects of the sand production problem 总被引:3,自引:0,他引:3
This paper examines the hydro-mechanical aspect of the sand production problem and sets the basic frame of the corresponding mathematical modelling. Accordingly, piping and surface erosion effects are studied on the basis of mass balance and particle transport considerations as well as Darcy's law. The results show that surface erosion is accompanied by high changes of porosity and permeability close to the free surface. Quantities which can be measured in experiment, like the amount of produced solids or fluid discharge, can be used in an inverse way to determine the constitutive parameters of the problem.Notation dV
Volume element
- dV
s
Volume of solids pt
- dV
v
Volume of voids
- dV
ff
Volume of fluid phase
- dV
fs
Volume of fluidized-particles
-
Volume of mixture
- dM
s
Mass of solids
- dM
ff
Mass of fluid phase
- d
M
fs
Mass of fluidized-particles
-
Mass of mixture
-
s
Density of solids
-
f
Density of fluid
-
ff
Density of fluid phase
-
fs
Density of fluidized-particles
-
Density of mixture
-
i
ff
Velocity of fluid
-
i
fs
Velocity of fluidized-particles
-
i
s
Velocity of solids
-
Velocity of mixture
-
q
ff
Volume-discharge of fluid
-
q
fs
Volume-discharge of fluidized-particles
-
Volume-discharge of mixture
-
m
ff
Mass-discharge of fluid
-
m
fs
Mass-discharge of fluidized-particles
-
Mass-discharge of mixture
-
er
Rate of mass-eroded
-
dep
Rate of mass-deposited
-
Mass generation term
- dS
i
Surface element
-
Pore-surface element
-
D
IJ
Tensor of mechanical dispersion
-
x
i
Location
-
t
Time
-
Porosity
-
c
Transport concentration
-
c
cr
Critical value ofc
-
p
Fluid-pressure
-
k
Permeability coefficient
-
k
Kinematic viscosity
-
Spatial frequency of erosion starter points 相似文献
102.
采用阴离子交换色谱法对成都地区的秋季雨水中常见的无机阴离子含量进行了测定,测定结果反映了该地区秋季大气污染的状况。 相似文献
103.
M. L. Illingsworth B. A. Banks J. W. Smith D. Jayne R. G. Garlick S. K. Rutledge K. K. de Groh 《Plasma Chemistry and Plasma Processing》1996,16(2):209-225
Glassy residues of the complex bis(N,N-disalicylidene-1,2-phenylenediamino)zirconium(IV), Zr(dsp)2, on glass slides were exposed to atomic oxygen in a plasma asher or an atomic beam facility for various amounts of lime in order to study the erosion process, determine the rate of erosion, and learn the chemical identity of the residue. The exposed films were characterized by weight loss, optical photography, profilometry, diffuse reflectance and total transmittance spectroscopy, scanning electron microscopy (SEM) with wavelength dispersive X-ray spectrometry (WDS), X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). Results indicate that these films erode much more slowly polyimide (Kapton) film under identical conditions, that the erosion is very nonuniform, and that zirconium dioxide is the predominant product after extended exposure. This complex is currently being evaluated as a polymer additive. 相似文献
104.
Experimental results are presented for electrode erosion on copper electrodes in magnetically rotated arcs in argon and helium. Measurements were also made of the arc voltage and velocity. The effects due to the contamination of the electrode surface by either a native contaminant layer (copper oxide and carbon traces) or the continuous injection of very small amounts of various diatomic gases (nitrogen, oxygen, chlorine, and carbon monoxide) into the inert plasma gases were determined. The erosion rates for pure argon were significantly higher than those for pure helium (13.5 g/C for argon and 1 g/C for helium) and with both gases, very high arc velocities were measured initially (>60 m/s for argon and >160 m/s for helium) when a natural contaminant layer was still present on the cathode. The removal of this layer resulted in lower velocities (2m/s for argon and 20m/s for helium) and higher erosion rates. The removal of the layer was much faster with argon, due possibly to higher electrode surface current densities for argon arcs. 相似文献
105.
106.
针对直线变压器驱动源(LTD)对开关的长寿命需求,基于前期研制的200kV低抖动多间隙气体开关电极几何参数以及开关通流水平,详细开展了不同电极材料(钼、黄铜、铜钨合金、高密度石墨、304和321不锈钢)的烧蚀性能实验。实验结果表明,在单次电荷转移量15.4mC,脉冲电流20kA条件下,体积烧蚀速率从大到小依次为:石墨、黄铜、铜钨合金、钼、不锈钢。电极烧蚀微观形貌分析表明,不锈钢是用于LTD开关相对较好的电极材料。根据不锈钢电极的体积烧蚀速率,可知理论上LTD开关的运行寿命可以超过1×106次,但前提是开关外壳需保持足够的绝缘强度。 相似文献
107.
以直径为0.1~0.6 mm的石英砂为磨料,黏度为10 mPa·s的原油为携砂液,在自制的冲蚀磨损试验装置上研究了含砂原油对石油防砂割缝筛管的冲蚀磨损性能,采用LW200-4CS数码倒置金相显微镜观测了筛管缝口表面的冲蚀磨损形貌;利用曲线拟合方法建立了割缝筛管冲蚀磨损率与原油流速、砂粒直径、砂粒浓度、冲蚀角之间关系的数学模型.结果表明:筛管的冲蚀磨损率随含砂原油流速的增加而成指数关系增加;开始时随着原油中所携带砂粒直径和浓度的增加,筛管的冲蚀磨损率增加,达到一定数值后砂粒直径和浓度再增加,割缝筛管的冲蚀磨损率反而降低;随着冲蚀角的增大,割缝筛管的冲蚀磨损率增加,在冲蚀角为90°时达到最大,这种现象不同于塑性材料的冲蚀磨损机理;所建立的数学模型与试验结果较吻合. 相似文献
108.
高速水流中旋涡空化所引起的空蚀和振动 总被引:5,自引:1,他引:5
为了研究旋涡空化所引起的空蚀和振动观象以及二者的关系,采用高速摄影的方法,观察了发生在射流放水阀山部的空化形态。采用快速富里叶变换(FFT)分析了空化所引起的振动。采用失重法,进行了空蚀实验。结果表明,旋涡空化能引起严重的空蚀和剧烈的振动。在旋涡空化发展的个同阶段,其所导致的振动和空蚀呈观了个同的特性。当Sσ>0.74时,随空化数的变化,振动和空蚀呈现了相同的变化趋势,但是,在0.50<σ<0.74的范围内,振动和空蚀呈现了相反的变化趋势。这是由于水流中空化旋涡的数目和形态随空化数的变化,以及旋涡空化引起振动和空蚀的机理不同所造成的。 相似文献
109.
Kimitaka KAWAMURA 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2023,99(1):1
Low molecular weight monocarboxylic acids (LMW monoacids, C1–C10) are the most abundant gaseous organic compound class in the atmosphere. Formic or acetic acid is the dominant volatile organic compound (VOC) in Earth’s atmosphere. They can largely contribute to rainwater acidity, especially in the tropical forest, and react with alkaline metals, ammonia, and amines, contributing to new particle formation and secondary organic aerosol production. Gaseous and particulate LMW monoacids were abundantly reported in China. They can be directly emitted from fossil fuel combustion and biomass burring; however, the secondary formation is more important than primary emissions via the photochemical oxidation of anthropogenic and biogenic VOCs. In this paper, we review the distributions of LMW monoacids from urban, mountain, and marine sites as well as from rainwater and alpine snow samples and discuss their sources and formation mechanisms in the atmosphere. We also discuss their importance as cloud condensation nuclei (CCN) and provide future perspectives of LMW monoacids study in the warming world. 相似文献
110.
针对直线变压器驱动源(LTD)对开关的长寿命需求,基于前期研制的200 kV低抖动多间隙气体开关电极几何参数以及开关通流水平,详细开展了不同电极材料(钼、黄铜、铜钨合金、高密度石墨、304和321不锈钢 )的烧蚀性能实验。实验结果表明,在单次电荷转移量15.4 mC,脉冲电流20 kA条件下,体积烧蚀速率从大到小依次为:石墨、黄铜、铜钨合金、钼、不锈钢。电极烧蚀微观形貌分析表明,不锈钢是用于LTD开关相对较好的电极材料。根据不锈钢电极的体积烧蚀速率,可知理论上LTD开关的运行寿命可以超过1106次,但前提是开关外壳需保持足够的绝缘强度。 相似文献