全文获取类型
收费全文 | 1085篇 |
免费 | 55篇 |
国内免费 | 65篇 |
专业分类
化学 | 76篇 |
力学 | 398篇 |
综合类 | 11篇 |
数学 | 201篇 |
物理学 | 519篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 20篇 |
2021年 | 21篇 |
2020年 | 32篇 |
2019年 | 14篇 |
2018年 | 17篇 |
2017年 | 29篇 |
2016年 | 31篇 |
2015年 | 43篇 |
2014年 | 32篇 |
2013年 | 51篇 |
2012年 | 44篇 |
2011年 | 74篇 |
2010年 | 68篇 |
2009年 | 72篇 |
2008年 | 72篇 |
2007年 | 49篇 |
2006年 | 61篇 |
2005年 | 63篇 |
2004年 | 69篇 |
2003年 | 58篇 |
2002年 | 34篇 |
2001年 | 35篇 |
2000年 | 35篇 |
1999年 | 24篇 |
1998年 | 22篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 18篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1979年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1205条查询结果,搜索用时 15 毫秒
171.
The integrability character of nonlinear equations of motion of two-dimensional gravity with dynamical torsion and bosonic string coupling is studied in this paper. The space-like and time-like first integrals of equations of motion are also found. 相似文献
172.
CHEN Bin ZHANG Jun-Feng 《理论物理通讯》2005,44(9)
We construct the two-flux colliding plane wave solutions in higher-dimensional gravity theory with dilaton,and two complementary fluxes. Two kinds of solutions have been obtained: Bell-Szekeres (BS) type and homogeneous type. After imposing the junction condition, we find that only the BS type solution is physically well-defined. Furthermore, we show that the future curvature singularity is always developed for our solutions. 相似文献
173.
在分数导数粘弹性本构模型的基础上综合考虑桩周土和桩芯土的平衡方程和几何方程建立了桩周土和桩芯土的竖向运动的控制方程.在频率域内利用分离变量法和分数导数的性质求解了桩周土和桩芯土竖向振动控制方程.考虑管桩与桩周土、管桩与桩芯土的边界连续性条件以及三角函数的正交性得到了分数导数粘弹性模型描述的土中管桩的竖向振动,通过数值分析研究了管桩和土体模型参数和几何参数对管桩的桩顶复刚度的影响规律.结果显示:桩芯土本构模型的分数导数的阶数对管桩竖向振动的影响较桩周土本构模型的阶数要小,且与频率有一定关系;桩芯土与桩周土的模型参数比τ1 和τ2 对等效阻尼的影响较对刚度因子的影响要大;管桩桩周和桩芯的直径比d 越小,管桩复刚度的实部和虚部就越大;土体力学性能对管桩竖向振动的影响要比管桩桩身力学性能的影响小. 相似文献
174.
随着深井、超深井数量的快速增加, 钻柱振动导致的钻具失效问题更加突出. 针对钻柱振动的研究可分为理论与数值模拟、测量分析两种方法. 由于钻柱振动具有复杂的非线性特征, 使得理论与数值模拟研究受到了很大限制, 因此井下振动测量技术的研究显得尤为重要. 本文比较全面和系统地介绍了国内外钻柱振动测量技术研究现状和进展情况, 并对几个应用较为成熟的国外测量系统的工作原理、分析方法及应用技术进行了详细的综述. 所得结论可为我国井下振动测量技术的发展提供重要参考. 相似文献
175.
The purpose of this paper is to present an efficient analytic method for obtaining the deformation of thin straight pipes, subjected to prescribed edge displacements or concentrated loads.The approach uses the mixed formulation where unknown functions are combined with trigonometric terms. A variational procedure is used to obtain the system of ordinary differential equations. For the applied load a Fourier approach is used to represent the load as an analytical function. For the prescribed displacement, three solutions for the ovalization are evaluated and a method based on energy contribution of each term is used to obtain their superposition.In contrast to finite element method the proposed method is efficient and can be applied to other boundary condition problems leading to continuous displacement and stress fields with a low number of unknowns. Comparisons with experimental and finite element procedures show good agreement that enhances the merits of the analytical solutions proposed.The value of this method is based on solving the differential equations rather than using commercial codes. So far, the solution of prescribed edge displacements has been limited to one term. This paper discusses how to add further terms using the mixed formulation, thus, presenting a novel procedure. 相似文献
176.
The optimal transient growth process of perturbations driven by the pressure gradient is studied in a turbulent pipe flow. A new computational method is proposed, based on the projection operators which project the governing equations onto the subspace spanned by the radial vorticity and radial velocity. The method is validated by comparing with the previous studies. Two peaks of the maximum transient growth amplification curve are found at different Reynolds numbers ranging from 20 000 to 250 000. The optimal flow structures are obtained and compared with the experiments and DNS results. The location of the outer peak is at the azimuthal wave number n=1, while the location of the inner peak is varying with the Reynolds number. It is observed that the velocity streaks in the buffer layer with a spacing of 100δv are the most amplified flow structures. Finally, we consider the optimal transient growth time and its dependence on the azimuthal wave length. It shows a self-similar behavior for perturbations of different scales in the optimal transient growth process. 相似文献
177.
178.
179.
Total reaction and fusion cross sections at sub- and near-barrier energies for the system 7Li + 28Si
A. Pakou K. Rusek N. Alamanos X. Aslanoglou M. Kokkoris A. Lagoyannis T. J. Mertzimekis A. Musumarra N. G. Nicolis D. Pierroutsakou D. Roubos 《The European Physical Journal A - Hadrons and Nuclei》2009,39(2):187-194
Fusion cross sections are extracted for the 7Li$ + $28Si system, via reaction cross section and transfer measurements at sub- and near-barrier energies ( E
lab = 5.7 to 14MeV). The energy evolution of transfer to reaction cross section ratios is determined with the aid of CDCC calculations,
which subsequently allows the deduction of fusion cross sections at sub- and near-barrier energies. It is shown that fusion
can be well represented in a BPM context. Fusion cross sections are compared for the systems 7Li$ + $28Si and 6Li$ + $28Si, the latter studied previously, and are found to exhibit different strengths. Last, the direct channels determined at 13MeV,
are found to be dominated by a 2n -transfer mechanism. 相似文献
180.