全文获取类型
收费全文 | 4060篇 |
免费 | 379篇 |
国内免费 | 437篇 |
专业分类
化学 | 1854篇 |
晶体学 | 35篇 |
力学 | 822篇 |
综合类 | 62篇 |
数学 | 266篇 |
物理学 | 1837篇 |
出版年
2024年 | 3篇 |
2023年 | 32篇 |
2022年 | 46篇 |
2021年 | 101篇 |
2020年 | 102篇 |
2019年 | 164篇 |
2018年 | 96篇 |
2017年 | 153篇 |
2016年 | 177篇 |
2015年 | 127篇 |
2014年 | 162篇 |
2013年 | 365篇 |
2012年 | 208篇 |
2011年 | 262篇 |
2010年 | 166篇 |
2009年 | 233篇 |
2008年 | 196篇 |
2007年 | 264篇 |
2006年 | 254篇 |
2005年 | 262篇 |
2004年 | 206篇 |
2003年 | 187篇 |
2002年 | 144篇 |
2001年 | 117篇 |
2000年 | 115篇 |
1999年 | 127篇 |
1998年 | 100篇 |
1997年 | 96篇 |
1996年 | 82篇 |
1995年 | 49篇 |
1994年 | 49篇 |
1993年 | 41篇 |
1992年 | 39篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 18篇 |
1986年 | 12篇 |
1985年 | 7篇 |
1984年 | 13篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1976年 | 5篇 |
1973年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有4876条查询结果,搜索用时 31 毫秒
941.
Radiative transfer plays an important role in the numerical simulation of turbulent combustion. However, for the reason that combustion and radiation are characterized by different time scales and different spatial and chemical treatments, the radiation effect is often neglected or roughly modelled. The coupling of a large eddy simulation combustion solver and a radiation solver through a dedicated language, CORBA, is investigated. Two formulations of Monte Carlo method (Forward Method and Emission Reciprocity Method) employed to resolve RTE have been compared in a one-dimensional flame test case using three-dimensional calculation grids with absorbing and emitting media in order to validate the Monte Carlo radiative solver and to choose the most efficient model for coupling. Then the results obtained using two different RTE solvers (Reciprocity Monte Carlo method and Discrete Ordinate Method) applied on a three-dimensional flame holder set-up with a correlated-k distribution model describing the real gas medium spectral radiative properties are compared not only in terms of the physical behavior of the flame, but also in computational performance (storage requirement, CPU time and parallelization efficiency). To cite this article: J. Zhang et al., C. R. Mecanique 337 (2009). 相似文献
942.
A Lagrangian framework is set out to describe turbulent non-premixed combustion in high speed coflowing jet flows. The final aim is to provide a robust computational methodology to simulate, in various conditions, the underexpanded GH2/GO2 torch jet that is used to initiate combustion in an expander cycle engine. The proposed approach relies on an early modelling proposal of Borghi and his coworkers. The model is well suited to describe finite rate chemistry effects and its recent extension to high speed flows allows one to take the influence of viscous dissipation phenomena into account. Indeed, since the chemical source terms are highly temperature sensitive, the influence of viscous phenomena on the thermal runaway is likely to be all the more pronounced since the Mach number values are high. The validation of the extended model has been recently performed through the numerical simulation of two distinct well-documented experimental databases. Only a brief summary of this preliminary validation step is provided here. The main purpose of the present work is to proceed with the numerical simulation of geometries that bring together the essential peculiarities of the underexpanded GH2/GO2 torch. The behavior of the corresponding supersonic coflowing jet flames for various conditions is discussed in the light of computational results. To cite this article: J.-F. Izard, A. Mura, C. R. Mecanique 337 (2009). 相似文献
943.
Mikaël Orain Frdric Grisch Eric Jourdanneau Bjorn Rossow Christian Guin Brigitte Trtout 《Comptes Rendus Mecanique》2009,337(6-7):373-384
Simultaneous measurements of PLIF-kerosene and PLIF-OH have been successfully performed in a multipoint injection system for various overall equivalence ratio, air inlet temperature between 480 and 730 K and pressure up to 2.2 MPa. Single shot 2D-maps of the spatial distribution of kerosene vapour and OH radical in the combustor have been recorded with good signal-to-noise ratio. Results show that depending on the split between the pilot and the main injectors, the flame front exhibits a single or a double structure. Good spatial correlation between the repartition of the kerosene vapour and the position of the flame front was observed; in particular, no “dark zone” is observed between the fuel and the flame front. As temperature and pressure increase, fuel evaporation improves and the spatial distribution of OH radical becomes more homogeneous in the combustor, suggesting a partially-distributed combustion. To cite this article: M. Orain et al., C. R. Mecanique 337 (2009). 相似文献
944.
使用主值空间表示的各向同性塑性本构方程 总被引:1,自引:0,他引:1
针对各向同性材料,在内变量为标量的假定下,应用张量函数表示定理给出了其塑性应变增量的不变性表示.它的3个不可约基张量取决于应力张量、相互正交且共主轴.建立3个基张量构成的张量子空间与三维主值空间的对应关系,将共主轴的张量采用笛卡尔坐标系中的矢量描述,矢量在不同坐标系下的分量均为张量的一组不可约不变量.定义塑性应变增量对应的矢量为内变量增量,使用张量函数表示理论得到,内变量演化方程除取决于应力对应的矢量和内变量本身外,还取决于应力增量在张量子空间中的投影,该投影就是应力对应矢量的增量,因此,本构方程归结为确定主值空间中矢量之间的关系.最后表明,三维主值空间与张量子空间中的流动法则是等价的. 相似文献
945.
V. Di Sarli A. Di Benedetto G. Russo S. Jarvis E. J. Long G. K. Hargrave 《Flow, Turbulence and Combustion》2009,83(2):227-250
In gas explosions, the unsteady coupling of the propagating flame and the flow field induced by the presence of blockages
along the flame path produces vortices of different scales ahead of the flame front. The resulting flame–vortex interaction
intensifies the rate of flame propagation and the pressure rise. In this paper, a joint numerical and experimental study of
unsteady premixed flame propagation around three sequential obstacles in a small-scale vented explosion chamber is presented.
The modeling work is carried out utilizing large eddy simulation (LES). In the experimental work, previous results (Patel
et al., Proc Combust Inst 29:1849–1854, 2002) are extended to include simultaneous flame and particle image velocimetry (PIV) measurements of the flow field within the
wake of each obstacle. Comparisons between LES predictions and experimental data show a satisfactory agreement in terms of
shape of the propagating flame, flame arrival times, spatial profile of the flame speed, pressure time history, and velocity
vector fields. Computations through the validated model are also performed to evaluate the effects of both large-scale and
sub-grid scale (SGS) vortices on the flame propagation. The results obtained demonstrate that the large vortical structures
dictate the evolution of the flame in qualitative terms (shape and structure of the flame, succession of the combustion regimes
along the path, acceleration-deceleration step around each obstacle, and pressure time trend). Conversely, the SGS vortices
do not affect the qualitative trends. However, it is essential to model their effects on the combustion rate to achieve quantitative
predictions for the flame speed and the pressure peak. 相似文献
946.
Among many presumed-shape pdf approaches for modeling non-premixed turbulent combustion, the presumed β-function pdf is widely used in the literature. However, numerical integration of the β-function pdf may encounter singularity difficulties at mixture fraction values of Z = 0 or 1. To date, this issue has been addressed by few publications. The present study proposes the Piecewise Integration
Method (PIM), an efficient, robust and accurate algorithm to overcome these numerical difficulties with the added benefit
of improving computational efficiency. Comparison of this method to the existing numerical integration methods shows that
the PIM exhibits better accuracy and greatly increases computational efficiency. The PIM treatment of the β-function pdf integration is first applied to the Burke–Schumann solution in conjunction with the k − ε turbulence model to simulate a CH4/H2 bluff-body turbulent flame. The proposed new method is then applied to the same flow using a more complex combustion model,
the laminar flamelet model. Numerical predictions obtained by using the proposed β-function pdf integration method are compared to experimental values of the velocity field, temperature and species mass fractions
to illustrate the efficiency and accuracy of the present method. 相似文献
947.
The internal modes of incoherent vector solitons (IVSs) in
photovoltaic photorefractive materials are investigated in the
framework of coupled nonlinear Schr\"{o}dinger equations. It is found
that there is a pair of internal modes corresponding to a
bright--bright IVS. The propagation dynamics of the bright-bright IVS
perturbed by the internal modes is simulated by numerical method. 相似文献
948.
Hong Zhang Ethan Tumarkin Ruby May A. Sullan Gilbert C. Walker Eugenia Kumacheva 《Macromolecular rapid communications》2007,28(5):527-538
Polymer microgels in the size range from several micrometers to hundreds of micrometers are used in the pharmaceutical, cosmetics, nutrition, pesticide, and food industries, as well as in the encapsulation of cells. To date, a broad range of strategies for the generation of polymer microgels exist, however, these methods involve multistage processes, do not utilize biocompatible components or do not allow precise control of the dimensions and internal structure of the microgels. Recently, microfluidic strategies for the production of polymer particles have offered precise control over the shapes, morphologies, and size distributions of polymer colloids. This paper discusses the most recent results obtained by the authors in the area of the microfluidic production of biopolymer microgels. It provides a brief review of the microfluidic methods for the continuous synthesis and fabrication of microgels, sets the criteria for the successful microfluidic generation of biomicrogels, and describes two methods for the preparation of microgels by microfluidic means. The article concludes with a summary and an outlook.
949.
用多极方法数值研究构成六重对称全内反射型光子晶体光纤各种结构参数对基模零色散点的调节.数值结果表明,在相对孔径较大时,包层空气孔柱层数不影响零色散点,在其它结构参数相同的条件下,空气孔直径越大,零色散点波长越短,而在其它结构参数相同的条件下,空气孔孔距越大,零色散点波长越长,当空气孔直径与空气孔孔距都很小时,零色散点出现在长波区域,当空气孔直径与空气孔孔距大到一定程度时,色散曲线在零色散线出现振荡特性,并出现多个零色散点,在包层空气柱层数一定的条件下,中央纤芯缺省空气孔层数对零色散点的调节范围大. 相似文献
950.
多目标多光谱辐射高速高温计的研制 总被引:1,自引:0,他引:1
固体火箭羽焰是一种特殊的火焰,固体火箭发动机喷管羽流沿径向和轴向的温度是研究固体推进剂燃烧状况和发动机燃烧流场的基本参数。针对固体火箭发动机尾喷焰温度及其空间分布测量的需要,继1999年采用多光谱辐射测温方法和技术实现航天某型号固体火箭发动机测量后,研制了新型的多目标多光谱辐射高速高温计用于固体火箭发动机地面搭载试验。仪器使用组合棱镜和光电二极管阵列实现目标0.4~1.1μm光谱的热辐射测量,在主光路设计中首次使用光纤技术,实现一台仪器同时测量空间分布6个目标点的温度和发射率,每个点的空间位置由光阑上的通光孔精确确定,且每个目标测点均有8个工作光谱,研制的同步高速数据采集系统完成48个测量通道的数据同步时间小于10 ns。 相似文献