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231.
爆坑是土中爆炸荷载作用下的主要响应形式,基于大型爆炸实验场地,开展了一系列低含水率砂土和饱和砂土中的爆炸成坑现场实验,研究了药量、埋深及含水率等因素对土中爆坑效应的影响。研究结果显示:根据药包的比例埋深,低含水率砂土场地的最终爆坑形态可以分为隐爆、塌陷型漏斗坑和抛掷型爆坑3类,发生封闭爆炸的临界比例埋深为2.3 m/kg1/3;形成抛掷型爆坑的条件为比例埋深小于1.5 m/kg1/3;当比例埋深为1.5~2.3 m/kg1/3时,形成塌陷型漏斗坑。土中孔隙水压力的增大导致坑壁周围土体发生了液化流动、坍塌,最终造成爆坑横向尺寸的扩大。相同爆源条件下,饱和砂土场地形成的坑面直径比低含水率砂土场地提高了25%~35%,饱和砂土场地发生封闭爆炸的极限比例埋深可达2.5 m/kg1/3。 相似文献
232.
DPTM simulation of aeolian sand ripple 总被引:1,自引:1,他引:1
Aeolian sand ripple and its time evolution are simulated by the discrete particle tracing method (DPTM) presented in this
paper. The difference between this method and the current methods is that the former can consider the three main factors relevant
to the formation of natural aeolian sand ripples, which are the wind-blown sand flux above the sand bed formed by lots of
sand particles with different diameters, the particle-bed collision and after it the rebound and ejection of sand particles
in the sand bed, the saltation of high-speed sand particles and the creep of low-speed sand particles, respectively. The simulated
aeolian sand ripple is close to the natural sand ripple not only in basic shape and characteristic, particle size segregation
and stratigraphy, but also in formation stages. In addition, three important speeds can be obtained by this method, which
are the propagation speed of the saturated aeolian sand ripple and the critical frictional wind speeds of emergence and disappearance
of sand ripple.
Supported by the Key Project of the National Natural Science Foundation of China (Grant No. 10532040) 相似文献
233.
A new isokinetic vertical sand trap is designed in this work, and the new trap has an advantage that airflows in all sampling tubes at different height can simultaneously approach the isokinetic state. The stagnant effect and vertical sand mass flux are experimentally investigated in a wind tunnel. Compared with the traditional passive sand trap, the new design greatly reduces the stagnant effect, and has higher efficiency at different heights and wind speeds. The results obtained in this Letter also show the stagnant effect of the sand trap not only changes the total efficiency of the sand collection, but also the distribution of the vertical sand flux. The new isokinetic sand trap has good performance and can be applied to study the sand flux in aeolian sand transport. 相似文献
234.
以油砂中钠元素为研究对象,首次应用近红外光谱,结合Lasso(least absolute shrinkage and selection operator)建模方法,建立了油砂金属钠含量的近红外光谱定量校正模型,并与传统的PLS建模方法进行比较。结果表明,两种方法建立的油砂金属钠含量校正模型都具有很高的精度,预测性能方面略有差异。在实验验证集与预测集中,PLS与Lasso算法的相关系数分别是:Rv=0.878 8,Rp=0.857 9和Rv=0.887 4,Rp=0.860 0。实验验证了使用近红外光谱快速测定油砂金属钠含量的有效性,并分析了PLS与Lasso算法的适用范围。 相似文献
235.
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237.
太赫兹波空间传输特性研究对于太赫兹波在空间中的应用具有重要意义.为研究太赫兹波在沙尘暴天气中的传输特性,本文根据沙尘粒子尺度的对数正态分布,应用Mie散射理论和Monte Carlo方法,分析了国内不同地域的六种干沙模态沙尘暴对1—10 THz频段太赫兹波的衰减特性,给出了消光参量和衰减率与频率的关系.结果表明,随着频率的增大,1—10 THz频段太赫兹波的衰减率呈先增加后减小的趋势,沙尘暴的模态不同,太赫兹波衰减较强的频段范围有所不同.为了分析沙粒含水量对太赫兹波传输衰减的影响,计算了不同尺寸的沙尘粒子3个效率因子与含水量的关系,发现粒子尺寸不同,含水量对消光的影响也不同;应用Monte Carlo方法计算了两种湿沙模态的沙尘暴对1—10 THz频段太赫兹波的衰减,给出了衰减率与含水量及频率的关系.结果表明,随沙粒含水量增大,沙尘暴对太赫兹波衰减较强的频段向低频方向移动,含水量小于5%时,太赫兹波衰减率随含水量增大显著增强,湿度较大的沙尘暴天气对太赫兹波的传输衰减影响更大. 相似文献
238.
为了解决岩石工程相似模型实验中传统相似材料难以模拟深部软岩低强度、大变形和强流变的问题,本文选用70#沥青(产量大、成本低、粘弹性、易成型、易软化等)和海砂作为深部软岩的相似模拟材料.采用连续加压法对其进行了单轴压缩实验,对不同配比下试件的密度、抗压强度及初始弹性模量进行分析,得到了该相似材料有关的原始数据和规律.本文初步验证了使用该相似材料模拟深部软岩的可行性,并针对不足之处给出一些合理改进建议,为进一步模型模拟实验提供指导. 相似文献
239.
With the PDPA (Phase Doppler Particle Analyzer) measurement technology, the probability distributions of particle impact and
lift-off velocities on bed surface and the particle velocity distributions at different heights are detected in a wind tunnel.
The results show that the probability distribution of impact and lift-off velocities of sand grains can be expressed by a
log-normal function, and that of impact and lift-off angles complies with an exponential function. The mean impact angle is
between 28° and 39°, and the mean lift-off angle ranges from 30° to 44°. The mean lift-off velocity is 0.81–0.9 times the
mean impact velocity. The proportion of backward-impacting particles is 0.05–0.11, and that of backward-entrained particles
ranges from 0.04 to 0.13. The probability distribution of particle horizontal velocity at 4 mm height is positive skew, the
horizontal velocity of particles at 20 mm height varies widely, and the variation of the particle horizontal velocity at 80
mm height is less than that at 20 mm height. The probability distribution of particle vertical velocity at different heights
can be described as a normal function.
Supported by the National Natural Science Foundation of China (Grant No. 10532030) and the National Basic Research Program
of China (Grant No. G2000048702) 相似文献
240.
Khaled A. Ramadan Mostafa K. Seddeek Abdelkareem Nijim Taher Sharshar 《Isotopes in environmental and health studies》2013,49(4):456-469
The radioactivity levels are poorly studied in non-coastal arid regions. For this reason, 38 locations covering an area of about 350 km2 in northeast Sinai, Egypt, were investigated by γ-ray spectroscopy. Moderately significant correlations among 238U, 234Th, and 226Ra isotopes and low significant correlations between the concentrations of 238U-series and 232Th in sand were obtained. No evidence of correlation was found between the concentrations of radioisotopes and pH, grain size, total organic matter content, bicarbonate or calcium carbonate concentrations of the sand samples. The mean values of soil-to-plant transfer factor were 0.15, 0.18, 1.52 and 0.74 for 226Ra, 232Th, 40K, and 137Cs, respectively. The range of concentrations of 226Ra, 232Th, and 40K in water samples collected from five wells were<0.4–0.16,<0.4–0.13, and<0.15–1.62 Bq l?1, respectively. The mean absorbed dose rate in outdoor air at a height of 1 m above the ground surface for the sand samples was 19.4 nGy h?1. The Raeq activities of the sands are lower than the recommended maximum value of 370 Bq kg?1 criterion limit for building materials. 相似文献