全文获取类型
收费全文 | 6270篇 |
免费 | 294篇 |
国内免费 | 192篇 |
专业分类
化学 | 866篇 |
晶体学 | 12篇 |
力学 | 3434篇 |
综合类 | 31篇 |
数学 | 351篇 |
物理学 | 2062篇 |
出版年
2024年 | 7篇 |
2023年 | 53篇 |
2022年 | 70篇 |
2021年 | 69篇 |
2020年 | 92篇 |
2019年 | 100篇 |
2018年 | 59篇 |
2017年 | 90篇 |
2016年 | 239篇 |
2015年 | 234篇 |
2014年 | 212篇 |
2013年 | 283篇 |
2012年 | 208篇 |
2011年 | 330篇 |
2010年 | 216篇 |
2009年 | 357篇 |
2008年 | 369篇 |
2007年 | 403篇 |
2006年 | 385篇 |
2005年 | 385篇 |
2004年 | 358篇 |
2003年 | 352篇 |
2002年 | 263篇 |
2001年 | 161篇 |
2000年 | 181篇 |
1999年 | 134篇 |
1998年 | 191篇 |
1997年 | 125篇 |
1996年 | 86篇 |
1995年 | 129篇 |
1994年 | 94篇 |
1993年 | 88篇 |
1992年 | 62篇 |
1991年 | 46篇 |
1990年 | 34篇 |
1989年 | 49篇 |
1988年 | 34篇 |
1987年 | 30篇 |
1986年 | 20篇 |
1985年 | 13篇 |
1984年 | 14篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1979年 | 19篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1973年 | 10篇 |
1972年 | 8篇 |
1971年 | 13篇 |
排序方式: 共有6756条查询结果,搜索用时 15 毫秒
51.
The properties of fluctuations in space in or outside thermal equilibrium are obtained by solving hierarchies of equations derived either from the Liouville or the Master equation. In particular we study the one-, two-, etc., time correlation functions that describe the spatial and temporal behavior of the fluctuations in space. Explicit solutions are obtained for a dilute gas. The Langevin approach is briefly discussed. Our results are compared with those obtained in the extensive literature, which is reviewed in some detail. 相似文献
52.
The third law of thermodynamics, in the sense that the entropy per unit volume goes to zero as the temperature goes to zero, is investigated within the framework of statistical mechanics for quantum and classical lattice models. We present two main results: (i) For all models the question of whether the third law is satisfied can be decided completely in terms of ground-state degeneracies alone, provided these are computed for all possible boundary conditions. In principle, there is no need to investigate possible entropy contributions from low-lying excited states, (ii) The third law is shown to hold for ferromagnetic models by an analysis of the ground states.Dedicated to Pierre Résibois. Work supported in part by NSF grant PHY-7825390 A01. 相似文献
53.
We prove theH-stability property and the existence of the thermodynamic limit of the free energy density of the two-dimensional, one-component classical plasma. We give lower and upper bounds on the free energy density in any dimensionv and draw some consequences. 相似文献
54.
Zhenjun Yang 《Acta Mechanica Sinica》2006,22(3):243-256
The scaled boundary finite element method (SBFEM) is a recently developed numerical method combining advantages of both finite element methods (FEM) and boundary element methods (BEM) and with its own special features as well. One of the most prominent advantages is its capability of calculating stress intensity factors (SIFs) directly from the stress solutions whose singularities at crack tips are analytically represented. This advantage is taken in this study to model static and dynamic fracture problems. For static problems, a remeshing algorithm as simple as used in the BEM is developed while retaining the generality and flexibility of the FEM. Fully-automatic modelling of the mixed-mode crack propagation is then realised by combining the remeshing algorithm with a propagation criterion. For dynamic fracture problems, a newly developed series-increasing solution to the SBFEM governing equations in the frequency domain is applied to calculate dynamic SIFs. Three plane problems are modelled.
The numerical results show that the SBFEM can accurately predict static and dynamic SIFs, cracking paths and load-displacement curves, using only a fraction of degrees of freedom generally needed by the traditional finite element methods.The project supported by the National Natural Science Foundation of China (50579081) and the Australian Research Council (DP0452681)The English text was polished by Keren Wang. 相似文献
55.
下承式梁拱组合桥梁的梁拱协作机理研究 总被引:1,自引:0,他引:1
文章将外部静定、内部高次超静定的梁拱组合桥梁分解成梁拱闭合体和吊杆两种构件,并且将吊杆力假定为膜张力,求解出了梁拱组合桥梁在均布荷载作用下拱肋分担的荷载大小及其修正系数,明确了其传力途径,定量地求出了梁拱分担的荷载比例,拱梁的拉压力偶矩大小以及梁拱截面的弯矩,并讨论了拱梁荷载比、弯矩比的影响因素及其关系,完整地揭示了下承式梁拱组合桥梁的梁拱协作机理. 相似文献
56.
In this paper, by capturing the atomic information and reflecting the behaviour governed by the nonlinear potential function,
an analytical molecular mechanics approach is proposed. A constitutive relation for single-walled carbon nanotubes (SWCNT’s)
is established to describe the nonlinear stress-strain curve of SWCNT’s and to predict both the elastic properties and breaking
strain of SWCNT’s during tensile deformation. An analysis based on the virtual internal bond (VIB) model proposed by P. Zhang
et al. is also presented for comparison. The results indicate that the proposed molecular mechanics approach is indeed an
acceptable analytical method for analyzing the mechanical behavior of SWCNT’s.
The project supported by the National Natural Science Foundation of China (10121202, 90305015 and 10328203), the Key Grant
Project of Chinese Ministry of Education (0306) and the Research Grants Council of the Hong Kong Special Administrative Region,
China (HKU 7195/04E). 相似文献
57.
通过建立力学模型,分析轿车冲撞行人的力学过程,对此进行了计算和讨论,进而得到与实验结果相吻合的使行人发生倒立时轿车车速的临界值.并提供了一种有效估算临界车速的方法. 相似文献
58.
本文简单地阐述了物理科学的发展电,在19世纪末期,物珲科学已经有相当发展,并形成了三个科学分支--研究物体运动,有牛顿力学;研究物质热运动,有热力学和统计力学;研究电磁波和光波,有电动力学,可是,这三种经典力学在20世纪初面临着新的挑战(困难),从而,相应地产生了三种新的基础理论,即狭义相对论,广义相对论;聚集理论,聚集力学;量子理论,量子力学,具体实践表明,它们在解决新的难题方面都取得很大成功. 相似文献
59.
The symmetries and non-Noether conservation laws of
Birkhoffian system with unilateral constraints are studied. The
differential equations of motion of the system are established,
and the criterions of Noether symmetry, Lie symmetry and Mei
symmetry of the system are given. Two types of new conservation
laws, called the Hojman conservation law and the Mei conservation
law respectively, are obtained, and the intrinsic relations among
the symmetries and the new conservation laws are researched.
At the end of the paper, an example is given to illustrate the
application of the results. 相似文献
60.
In the present paper the Lie symmetrical non-Noether conserved
quantity of the Poincaré-Chetaev equations of a generalized
classical mechanics under the general infinitesimal transformations
of Lie groups is discussed. First, we establish the determining
equations of Lie symmetry of the equations. Second, the Lie symmetrical
non-Noether conserved quantity of the equations is deduced. Finally,
an example is given to illustrate the application of the results. 相似文献