全文获取类型
收费全文 | 217篇 |
免费 | 5篇 |
专业分类
化学 | 57篇 |
晶体学 | 1篇 |
力学 | 8篇 |
物理学 | 156篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 4篇 |
2016年 | 1篇 |
2014年 | 4篇 |
2013年 | 13篇 |
2012年 | 16篇 |
2011年 | 23篇 |
2010年 | 16篇 |
2009年 | 12篇 |
2008年 | 17篇 |
2007年 | 15篇 |
2006年 | 14篇 |
2005年 | 8篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 9篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有222条查询结果,搜索用时 31 毫秒
91.
92.
93.
Franck Richecoeur Sbastien Ducruix Philippe Scouflaire Sbastien Candel 《Proceedings of the Combustion Institute》2009,32(2):1663-1670
This article considers the influence of fluctuations in temperature on acoustic resonance characteristics of a combustion chamber. This analysis is concerned with acoustic coupling experienced in high frequency instabilities. Experiments carried out on a multiple injector combustor (MIC) operating with liquid oxygen and gaseous methane are used to simulate on a model scale the situation prevailing in a liquid rocket thrust chamber. External acoustic modulations are generated by periodically blocking an auxiliary nozzle with a rotating toothed wheel. By continuously changing the rotation velocity, it is possible to apply a linear frequency sweep and obtain the response of the system to an external excitation. It is found that the chamber quality factor under hot fire conditions is reduced with respect to the one measured under cold flow conditions. This is shown to be correlated with the level and spatial extension of temperature fluctuations inside the chamber. Temperature fluctuations induce variations in the speed of sound which in turn perturb the eigenfrequencies of the system and modify its response. This effect is modeled in a simplified way by considering a second order dynamical system featuring an eigenfrequency which fluctuates around its mean value. The dynamics is analyzed by making use of simulations and by the method of averaging. It is shown that when the eigenfrequency fluctuates, the system behaves as if it had an augmented level of dissipation and that this induces a reduction in the quality factor. It is concluded that this mechanism could have an important impact on the development of oscillations in liquid rocket engines. 相似文献
94.
C. Laurent L. Esclapez D. Maestro G. Staffelbach B. Cuenot L. Selle T. Schmitt F. Duchaine T. Poinsot 《Proceedings of the Combustion Institute》2019,37(4):5147-5154
High-fidelity numerical simulations are used to study flame root stabilization mechanisms of cryogenic flames, where both reactants (O2 and CH4) are injected in transcritical conditions in the geometry of the laboratory scale test rig Mascotte operated by ONERA (France). Simulations provide a detailed insight into flame root stabilization mechanisms for these diffusion flames: they show that the large wall heat losses at the lips of the coaxial injector are of primary importance, and require to solve for the fully coupled conjugate heat transfer problem. In order to account for flame–wall interaction (FWI) at the injector lip, detailed chemistry effects are also prevalent and a detailed kinetic mechanism for CH4 oxycombustion at high pressure is derived and validated. This kinetic scheme is used in a real-gas fluid solver, coupled with a solid thermal solver in the splitter plate to calculate the unsteady temperature field in the lip. A simulation with adiabatic boundary conditions, an hypothesis that is often used in real-gas combustion, is also performed for comparison. It is found that adiabatic walls simulations lead to enhanced cryogenic reactants vaporization and mixing, and to a quasi-steady flame, which anchors within the oxidizer stream. On the other hand, FWI simulations produce self-sustained oscillations of both lip temperature and flame root location at similar frequencies: the flame root moves from the CH4 to the O2 streams at approximately 450 Hz, affecting the whole flame structure. 相似文献
95.
96.
FCC metals and alloys are frequently used in cryogenic applications, nearly down to the temperature of absolute zero, because of their excellent physical and mechanical properties including ductility. Some of these materials, often characterized by the low stacking fault energy (LSFE), undergo at low temperatures three distinct phenomena: dynamic strain ageing (DSA), plastic strain induced transformation from the parent phase (γ) to the secondary phase (α′) and evolution of micro-damage. The constitutive model presented in the paper is focused on the discontinuous plastic flow (serrated yielding) and takes into account the relevant thermodynamic background. The discontinuous plastic flow reflecting the DSA effect is described by the mechanism of local catastrophic failure of Lomer–Cottrell (LC) locks under the stress fields related to the accumulating edge dislocations (below the transition temperature from the screw dislocations to the edge dislocations mode T1). The failure of LC locks leads to massive motion of released dislocations accompanied by the step-wise increase of the strain rate. The response of stress is defined in terms of four stages within each serration cycle. In the fourth stage, the strain rate sensitivity model with temperature playing the role of relaxation parameter is applied. Identification of parameters of the constitutive model is based on the experimental data collected during a campaign of tensile tests carried out on copper and stainless steel samples immersed in liquid helium (4.5 K), by means of a unique equipment developed at CERN. 相似文献
97.
采用由SRK方程计算得出的混合工质物性参数,将具有相变两相流体物性分三部分处理,得出混合工质分段物性数据拟合曲线,并输入FLUENT软件的材料物性数据文件中,作为数值模拟物性参数数据。在上述物性数据处理的基础上,对混合工质天然气液化装置中换热器采用分段方式进行稳态数值模拟研究,得到沿长度方向一定温度下传热系数、压力梯度的变化曲线。通过与MUSE软件数据比较,计算结果有一定合理性,所得结论为有相变换热的混合工质低温板翅式换热器的设计和优化提供一定参考。 相似文献
98.
Pyrene-1-carboxy acid has a pK of 4 in the ground state, and a pK of 8 in the excited state. Fluorescence spectra of the acid and base forms are presented as a function of solvent and temperature.
Ab initio quantum calculations indicate that the bond between the ring system and the carboxyl group has aromatic character
that becomes stronger upon excitation. This stabilization helps to account for the increase in pK upon excitation. 相似文献
99.
本文以液氢温区下的双温区多管道为研究对象, 对其进行了热流分析, 建立了几何模型, 采用有限元方法进行了热-结构耦合分析求解, 分析了不同壁厚及不同支撑宽度下漏热、 应力及形变的变化规律. 研究结果表明: 壁厚减小时, 漏热值减少, 绝热支撑总体应力增加, 支撑形变增大; 宽度减小时,20 K 温区漏热量减少,80 K 温区漏热增加, 总漏热量减少, 支撑应力增大, 最大形变量增大. 最终, 针对某工程使用的双温区四管道, 拟合出了壁厚与漏热、 最大应力及最大形变量变化规律的曲线、 方程, 宽度与双温区漏热、 最大应力及最大形变量变化规律的曲线、 方程. 在应力、 漏热、 形变量均允许的情况下, 得出最薄壁厚可取到1 .576 mm; 在壁厚取为2 mm 时, 得出最小宽度可取为0.572 mm. 相似文献
100.