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511.
We provide the first direct comparisons, to our knowledge, of complex 3D micro cracking initiation and propagation in heterogeneous quasi-brittle materials modelled by the phase field numerical method and observed in X-ray microtomography images recorded during in situ mechanical testing. Some material parameters of the damage model, including the process zone (internal) length, are identified by an inverse approach combining experimental data and 3D simulations. A new technique is developed to study the micro cracking at a finer scale by prescribing the local displacements measured by digital volume correlation over the boundary of a small sub-volume inside the sample during the numerical simulations. The comparisons, performed on several samples of lightweight plaster and concrete, show a remarkable quantitative agreement between the 3D crack morphology obtained by the model and by the experiments, without any a priori knowledge about the location of the initiation of the cracks in the numerical model. The results indicate that the crack paths can be predicted in a fully deterministic way in spite of the highly random geometry of the microstructure and the brittle nature of its constituents. 相似文献
512.
应用慢应变速率拉伸试验和电化学方法研究了湿硫化氢溶液中UNS J91450不锈钢的电化学行为对应力腐蚀开裂的影响.结果表明,本实验条件下UNS J91540不锈钢具有较高的SCC敏感性,并随着溶液pH的降低而明显增大.该不锈钢的电化学行为对它的腐蚀开裂(SCC)敏感性具有重要影响.开路电位下该不锈钢的SCC行为同时受氢脆作用和裂纹尖端阳极溶解作用的影响.在pH较低的介质中析氢电流较高而裂纹尖端阳极溶解作用略低,而在pH较高的介质中析氢电流较低而裂纹尖端的阳极溶解作用相对增强.氢脆作用对UNS J91540不锈钢SCC敏感性影响更显著. 相似文献
513.
514.
植被护坡中植物根系的阻裂增强机理研究 总被引:3,自引:0,他引:3
本文从复合材料的角度对植物根系的加固机理进行了分析,将含根系的岩土体看成一特殊的复合材料,其中岩土体为基体相材料,根系为增强相材料,根系犹如纤维,将对根土复合体起到阻裂增强作用.并运用能量原理对根系的阻裂增强作用进行了分析研究,得出根土复合体中某点的抗剪强度增量的计算公式及该点处根系的抗拔力和最大拔出长度的计算公式,得出某点抗剪强度增量主要与该点处根的面积比、面密度、长径比、抗拉强度、根士间的黏聚力及摩擦系数有关,及如果根系深入某点以下锚同段长度大于该点处的最大拔出长度,根系将被拉断的结论. 相似文献
515.
催化裂化过程中含硫化合物转化规律的研究 总被引:12,自引:3,他引:9
选择丁硫醚、叔丁硫醚、四氢噻吩和乙基苯基硫醚作为模化合物,在模拟固定床催化裂化微反装置上考察含硫化合物转化和分布规律,在催化裂化过程中,烷基硫醚可以完全转化,转化产物为硫化氢,反应条件对转化程度没有明显影响;环状含硫化合物的转化程度与反应条件、溶剂性质有关,转化产物主要为硫化氢和汪量噻吩,生产的噻吩可进一步发生烷基化反应,反应温度升高,溶剂供氢能力增强,硫化氢的收率增加;乙基苯基硫醚也可以完全转化,转化产物主要为硫化氢和苯硫酚,生成的苯硫酚可进一步发生烷基化反应,反应温度升高,溶剂供氢能力增强,硫化氢的收率增加。 相似文献
516.
517.
K. Ivanova 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):327-330
The two-dimensional Ausloos et al. model of fluid invasion, freezing and thawing in a porous medium is elaborated upon and investigated in order to take into
account the pore volume redistribution and conservation during freezing. The results are qualitatively different from previous
work, since the damaged pore sizes are found to be much less than the possible maximum value and is reached after a large
number of invasion-freezing-thawing cycles, e.g. the material is “slowly damaged”. The pore size distribution is thus found in better agreement with expected practical findings.
The successive invasion percolation clusters are still found to be self-avoiding with aging. The cluster size decreases with
a power law as a function of invasion-frost-thaw iterations. The aging kinetics is also discussed through the normalized totally
invaded pore volume.
Received 24 September 1999 and Received in final form 5 January 2000 相似文献
518.
《Particuology》2017
Two modes of gas-solid riser operation, i.e., fluid catalytic cracking (FCC) and circulating fluidized bed combustor (CFBC), have been recognized in literature; particularly in the understanding of choking phenomena. This work compares these two modes of operation through computational fluid dynamics (CFD) simulation. In CFD simulations, the different operations are represented by fixing appropriate boundary conditions: solids flux or solids inventory. It is found that the FCC and CFBC modes generally have the same dependence of solids flux on the mean solids volume fraction or solids inventory. However, during the choking transition, the FCC mode of operation needs more time to reach a steady state; thus the FCC system may have insufficient time to respond to valve adjustments or flow state change, leading to the choking. The difference between FCC and CFBC systems is more pronounced for the systems with longer risers. A more detailed investigation of these two modes of riser operation may require a three-dimensional full loop simulation with dynamic valve adjustment. 相似文献
519.
《Particuology》2017
Gas–solid flow in a fluid catalytic cracking (FCC) riser exhibits poor mixing in the form of a core–annulus flow pattern and a dense bottom/dilute top distribution of solids. To enhance gas–solid mixing, studies on dense fluidized beds have suggested using a pulsating flow of gas. The present study investigates the effect of pulsating flow on gas–solid hydrodynamics inside the FCC riser employing computational fluid dynamics. Two flow conditions are investigated: a cold flow of air-FCC catalyst in a pilot-scale riser and a reactive flow in an industrial-scale FCC riser. In the cold-flow riser, pulsating flows cause the slug flow of solids and thus increase the average solid accumulation in the flow domain and solid segregation towards the wall. In the industrial FCC riser, pulsating flows produce radial profiles that are more homogeneous. Pulsating flows further improve the conversion and yield in the initial few metres of height. At 7 m, the conversion from pulsating flow is 59%, compared with 44% in without pulsating flow. The results and analysis presented here will help optimize flow conditions in the circulating fluidized bed riser, in not only FCC but also applications such as fast pyrolysis and combustion. 相似文献
520.