全文获取类型
收费全文 | 269593篇 |
免费 | 2421篇 |
国内免费 | 628篇 |
专业分类
化学 | 143647篇 |
晶体学 | 4177篇 |
力学 | 11969篇 |
综合类 | 9篇 |
数学 | 29618篇 |
物理学 | 83222篇 |
出版年
2019年 | 2304篇 |
2018年 | 3130篇 |
2017年 | 3125篇 |
2016年 | 4516篇 |
2015年 | 2699篇 |
2014年 | 4328篇 |
2013年 | 10746篇 |
2012年 | 8152篇 |
2011年 | 9976篇 |
2010年 | 7135篇 |
2009年 | 6940篇 |
2008年 | 9388篇 |
2007年 | 9589篇 |
2006年 | 8971篇 |
2005年 | 8151篇 |
2004年 | 7492篇 |
2003年 | 6789篇 |
2002年 | 6725篇 |
2001年 | 7396篇 |
2000年 | 5732篇 |
1999年 | 4393篇 |
1998年 | 3896篇 |
1997年 | 3875篇 |
1996年 | 3631篇 |
1995年 | 3362篇 |
1994年 | 3536篇 |
1993年 | 3215篇 |
1992年 | 3708篇 |
1991年 | 3692篇 |
1990年 | 3622篇 |
1989年 | 3482篇 |
1988年 | 3591篇 |
1987年 | 3492篇 |
1986年 | 3310篇 |
1985年 | 4389篇 |
1984年 | 4653篇 |
1983年 | 3899篇 |
1982年 | 4034篇 |
1981年 | 3952篇 |
1980年 | 3925篇 |
1979年 | 3897篇 |
1978年 | 4209篇 |
1977年 | 4120篇 |
1976年 | 4186篇 |
1975年 | 3866篇 |
1974年 | 3904篇 |
1973年 | 4067篇 |
1972年 | 2870篇 |
1971年 | 2389篇 |
1970年 | 2188篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
The effect of crack tip sharpness on crack propagation in vulcanized rubbers has been studied. For very sharp cracks, tearing is found to occur on a small scale at very low energies not far above the threshold required for the onset of mechanical crack growth. The “small-scale” tearing energies show relatively little variation for rubbers that differ widely in tear strength as normally measured. Thus the latter property appears to be strongly influenced by variations in the ability of rubbers to promote tip blunting. The small-scale tear behavior is of relevance to other fracture phenomena, including cutting by sharp objects and tensile failure. Natural variations in tip sharpness occur during cyclic or time-dependent mechanical crack growth and influence the form of the crack growth characteristics. 相似文献
902.
G. Lazarides C. Panagiotakopoulos Q. Shafi 《Zeitschrift fur Physik C Particles and Fields》1987,34(4):553-554
We discuss gauge models based on a superstring motivated rank six subgroup ofE 6. Lepton number is an accidental unbroken symmetry of the models which leads to an essentially stable proton. One of the neutral gauge bosons couples toB-L and may have mass below a TeV. 相似文献
903.
We study the approximability of minimum total weighted tardiness with a modified objective which includes an additive constant. This ensures the existence of a positive lower bound for the minimum value. Moreover the new objective has a natural interpretation in just-in-time production systems. 相似文献
904.
In this article we investigate some integral functional inequalities of Bellman–Bihari type for piecewise-continuous functions with some fixed points of discontinuity. We also prove a new analogy and generalization of results which were obtained by Bellman and Bihari to integro-sum inequalities with delay and discontinuities that do not belong to Lipschitz’s type. 相似文献
905.
906.
The stress-strain state of multilayered plates on an undeformable foundation is investigated. The design diagram of a transversely
loaded plate is formed by supplementing it with a symmetric one about the contact surface of the foundation. The double-thickness
plate obtained becomes loaded bilaterally and symmetrically about its midsurface. In such a way, only unflexural deformations
can be modeled, which reduces the number of unknowns and the general order of differentiation of the resolving system of equations.
The refined continual model developed takes into account the deformations of transverse shear and transverse compression in
high iterative approximations. The cases of a rigid contact between the foundation and the plate and frictionless slip of
the plate over the foundation are considered. Calculations confirm the efficiency of such an approach, which allows one to
obtain solutions qualitatively and quantitatively close to three-dimensional ones.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 643–654, September–October, 2006. 相似文献
907.
Nanometer scale Al/AlN multilayers have been prepared by dc magnetron sputtering technique with a columnar target. A set of Al/AlN multilayers with the Al layer thickness of 2.9 nm and the AlN layer thickness variation from 1.13 to 6.81 nm were determined. Low angle X-ray diffraction (LAXRD) was used to analyze the layered structure of multilayers. The phase structure of the coatings was investigated with grazing angle XRD (GAXRD). Mechanical properties of these multilayers were thoroughly studied using a nanoindentation and ball-on-disk micro-tribometer. It was found that the multilayer hardness and reduced modulus showed no strong dependence on the AlN layer thickness. Al2.9 nm/AlN1.13 nm multilayer had more excellent tribological properties than single layers and other proportion multilayers with a lowest friction coefficient of 0.15. And the tribological properties of all the multilayers are superior to the AlN single layer. 相似文献
908.
909.
A generalized linear differential equation in a Banach space is studied. The construction of a phase space and solutions with the help of the spectral theory of linear operators, ergodic theorems, and degenerate semigroups of linear operators is carried out. 相似文献
910.
The lanthanide sulfotellurides (LS)2Te1+x (0 ≤ x < 0.50) show order-disorder phenomena. Above 450°C, they crystallize in a partially disordered structure, orthorhombic with cell parameters a, b, and c close to 4.1, 5.2, and 13.6 Å, respectively. This structure is determined from diffractometer data on a (HoS)2Te1.34 crystal (R = 0.061). It is built up along the c axis from (L4S) tetrahedra layers, separated by Te planes. Disorder and nonstoichiometry are related to the two vacant Te sites. 相似文献