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234.
Finite element modelling of solidification in sand castings employing an implicit—explicit algorithm
The finite element method is used to model the solidification process in a sand casting. With a relatively coarse mesh, there is good agreement between numerical and experimental results. An implicit-explicit time-stepping algorithm demonstrated significant computer time savings when the appropriate solver was implemented. Consideration is also given to the problem of capacitance matrix lumping when quadratic elements are employed. 相似文献
235.
水合氧化铁/石英砂吸附剂的制备及性质 总被引:2,自引:0,他引:2
用反复沉淀法和加热蒸发法制备了水合氧化铁/石英砂水处理吸附剂,用电子显微镜观察了它们的表面形态,测定了氧化铁在表面上的附着能力,研究了该吸附剂对重金属离子的吸附和脱附性质.结果表明,加热蒸发法所得样品表面形态复杂;在酸性溶液和机械振荡条件下表面氧化铁有良好附着能力;对Cd2+和Cr3+有较强的吸附性质. 相似文献
236.
Cíntia S. Silva Cassiana S. Nomura Joaquim A. Nóbrega Pedro V. Oliveira 《Mikrochimica acta》2008,161(1-2):109-114
A fast and reliable method for the direct determination of iron in sand by solid sampling graphite furnace atomic absorption
spectrometry was developed. A Zeeman-effect 3-field background corrector was used to decrease the sensitivity of spectrometer
measurements. This strategy allowed working with up to 200 μg of samples, thus improving the representativity. Using samples
with small particle sizes (1–50 μm) and adding 5 μg Pd as chemical modifier, it was possible to obtain suitable calibration
curves with aqueous reference solutions. The pyrolysis and atomization temperatures for the optimized heating program were
1400 and 2500 °C, respectively. The characteristic mass, based on integrated absorbance, was 56 pg, and the detection limits,
calculated considering the variability of 20 consecutive measurements of platform inserted without sample was 32 pg. The accuracy
of the procedure was checked with the analysis of two reference materials (IPT 62 and 63). The determined concentrations were
in agreement with the recommended values (95% confidence level). Five sand samples were analyzed, and a good agreement (95%
confidence level) was observed using the proposed method and conventional flame atomic absorption spectrometry. The relative
standard deviations were lower than 25% (n = 5). The tube and boat platform lifetimes were around 1000 and 250 heating cycles, respectively.
Correspondence: Pedro V. Oliveira, Instituto de Química, Universidade de S?o Paulo, CP 26077, 05513-970 S?o Paulo, SP, Brazil 相似文献
237.
采用直锥变截面式Φ74mm分离式霍普金森压杆,对不同替代率沙漠砂混凝土进行冲击压缩实验,得到了不同替代率沙漠砂混凝土在不同应变率下的应力应变曲线。分析应变率对沙漠砂混凝土峰值应力、峰值应变和比能量影响,揭示了沙漠砂替代率对沙漠砂混凝土峰值应力影响规律,并对沙漠砂混凝土动态破坏模式进行研究。研究表明:随着应变率增加,沙漠砂混凝土峰值应力、强度增强因子、比能量和峰值应变逐渐增大;在同一应变率下,随着替代率增加,沙漠砂混凝土峰值应力逐渐减小。本文研究结果可为沙漠砂在工程中的应用提供指导和借鉴。 相似文献
238.
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
239.
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
240.
Fluid-particle interaction underpins important behavior of granular media. Particle-scale simulation may help to provide key microscopic information governing the interaction and offer better understanding of granular media as a whole. This paper presents a coupled computational fluid dynamics and discrete element method (CFD-DEM) approach for this purpose. The granular particle system is modeled by DEM, while the fluid flow is simulated by solving the locally averaged Navier–Stokes equation with CFD. The coupling is considered by exchanging such interaction forces as drag force and buoyancy force between the DEM and CFD. The approach is benchmarked by two classic geomechanics problems for which analytical solutions are available, and is further applied to the prediction of sand heap formation in water through hopper flow. It is demonstrated that the key characteristic of granular materials interacting with pore water can be successfully captured by the proposed method. 相似文献