全文获取类型
收费全文 | 7744篇 |
免费 | 1270篇 |
国内免费 | 519篇 |
专业分类
化学 | 2605篇 |
晶体学 | 86篇 |
力学 | 1669篇 |
综合类 | 86篇 |
数学 | 755篇 |
物理学 | 4332篇 |
出版年
2024年 | 12篇 |
2023年 | 49篇 |
2022年 | 167篇 |
2021年 | 169篇 |
2020年 | 201篇 |
2019年 | 218篇 |
2018年 | 162篇 |
2017年 | 217篇 |
2016年 | 280篇 |
2015年 | 323篇 |
2014年 | 356篇 |
2013年 | 1044篇 |
2012年 | 441篇 |
2011年 | 533篇 |
2010年 | 380篇 |
2009年 | 428篇 |
2008年 | 417篇 |
2007年 | 441篇 |
2006年 | 382篇 |
2005年 | 384篇 |
2004年 | 375篇 |
2003年 | 286篇 |
2002年 | 285篇 |
2001年 | 242篇 |
2000年 | 180篇 |
1999年 | 153篇 |
1998年 | 197篇 |
1997年 | 167篇 |
1996年 | 131篇 |
1995年 | 132篇 |
1994年 | 112篇 |
1993年 | 119篇 |
1992年 | 99篇 |
1991年 | 66篇 |
1990年 | 54篇 |
1989年 | 48篇 |
1988年 | 57篇 |
1987年 | 38篇 |
1986年 | 34篇 |
1985年 | 30篇 |
1984年 | 25篇 |
1983年 | 5篇 |
1982年 | 21篇 |
1981年 | 19篇 |
1980年 | 7篇 |
1979年 | 17篇 |
1978年 | 7篇 |
1976年 | 4篇 |
1973年 | 4篇 |
1972年 | 5篇 |
排序方式: 共有9533条查询结果,搜索用时 15 毫秒
52.
The melting curve of MgSiO分子动力学 MgSiO3钙钛矿 熔化温度 高压 melting temperature, molecular dynamics, high pressure Project supported by the National Natural Science Foundation of China (Grant Nos 10274055 and 10376021),the Natural Science Foundation of Gansu Province, China (Grant No 3ZS051-A25-027) and the Scientific Research Foundation of Education Bureau of Gansu Province, China (Grant No 0410-01). 2005-01-12 5/8/2005 12:00:00 AM The melting curve of MgSiO3 perovskite is simulated using molecular dynamics simulations method at high pressure. It is shown that the simulated equation of state of MgSiO3 perovskite is very successful in reproducing accurately the experimental data. The pressure dependence of the simulated melting temperature of MgSiO3 perovskite reproduces the stability of the orthorhombic perovskite phase up to high pressure of 130GPa at ambient temperature, consistent with the theoretical data of the other calculations. It is shown that its transformation to the cubic phase and melting at high pressure and high temperature are in agreement with recent experiments. 相似文献
53.
S. Loridant G. LucazeauT. Le Bihan 《Journal of Physics and Chemistry of Solids》2002,63(11):1983-1992
A high-pressure structural study of SrCeO3 has been performed at room temperature by Raman spectroscopy and X-ray diffraction up to 32 and 45 GPa, respectively. A first-order reversible phase transition is observed at about 12 GPa in both techniques. A second weak structural change, taking place between 18 and 25 GPa, can be suspected from Raman data. The increase in the number of Raman bands and diffraction lines is an indication that the symmetry is lowered and the compound does not evolve towards the ideal cubic perovskite structure. A Rietveld analysis of X-ray data was performed for the low-pressure phase and the atomic positions and the cell lattice parameters variations are reported in this paper. The volume compressibility derived from Raman modes (5.6×10−12 Pa−1), involving mainly bond-stretching for each type of polyhedron, is found to be close to the one obtained from volume cell variations measured by X-ray diffraction (7.9×10−12 Pa−1). 相似文献
54.
Haim Gvirtzman Mordeckai Magaritz Eugenia Klein Arie Nadler 《Transport in Porous Media》1987,2(1):83-93
Cold stage Scanning Electron Microscopy (SEM) with a rapid cooling technique makes it possible to investigate the water phase within unsaturated porous media. It is thought that this technique preserves the main features of the micromorphology of the water menisci as it exists in the liquid phase in soils. Saddle-shaped elements, as well as pendular rings of water, were observed with concave and convex curvatures of the water-air interface. The hydraulic conductivity of an unsaturated soil may be inferred from SEM photographs. Observations of isolated water menisci indicate the existence of an immobile water domain. The surface geometry of the water menisci was analyzed quantitatively and surface tension and capillary pressure were determined. 相似文献
55.
S. Scott Collis Kaveh Ghayour Matthias Heinkenschloss Michael Ulbrich Stefan Ulbrich 《国际流体数值方法杂志》2002,40(11):1401-1429
The control of complex, unsteady flows is a pacing technology for advances in fluid mechanics. Recently, optimal control theory has become popular as a means of predicting best case controls that can guide the design of practical flow control systems. However, most of the prior work in this area has focused on incompressible flow which precludes many of the important physical flow phenomena that must be controlled in practice including the coupling of fluid dynamics, acoustics, and heat transfer. This paper presents the formulation and numerical solution of a class of optimal boundary control problems governed by the unsteady two‐dimensional compressible Navier–Stokes equations. Fundamental issues including the choice of the control space and the associated regularization term in the objective function, as well as issues in the gradient computation via the adjoint equation method are discussed. Numerical results are presented for a model problem consisting of two counter‐rotating viscous vortices above an infinite wall which, due to the self‐induced velocity field, propagate downward and interact with the wall. The wall boundary control is the temporal and spatial distribution of wall‐normal velocity. Optimal controls for objective functions that target kinetic energy, heat transfer, and wall shear stress are presented along with the influence of control regularization for each case. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
56.
The primary resource for quantum computation is Hilbert-space dimension. Whereas Hilbert space itself is an abstract construction, the number of dimensions available to a system is a physical quantity that requires physical resources. Avoiding a demand for an exponential amount of these resources places a fundamental constraint on the systems that are suitable for scalable quantum computation. To be scalable, the effective number of degrees of freedom in the computer must grow nearly linearly with the number of qubits in an equivalent qubit-based quantum computer. 相似文献
57.
抽吸和压力梯度在层流边界层转捩过程中的作用 总被引:1,自引:0,他引:1
用空间模式的二次稳定性理论研究了抽吸和压力梯度对边界层三维亚谐扰动流动稳定性的影响.数值结果表明,固体边界上的抽吸有明显的层流控制作用,逆压梯度则有较强的不稳定作用. 相似文献
58.
59.
The question about the definition of the “internal pressure” concept is being discussed. It is shown that the previously found differential relation between the cohesion energy density and the internal pressure is one of the examples of an absolutely general interrelation between definitely connected differential functions. It is ascertained that the ratio (the internal pressure divided by the cohesion energy density) is a structuresensitive parameter inherent to the calorific (thermal) equation of a liquid state. 相似文献
60.