全文获取类型
收费全文 | 389250篇 |
免费 | 3640篇 |
国内免费 | 1102篇 |
专业分类
化学 | 193255篇 |
晶体学 | 5356篇 |
力学 | 19260篇 |
综合类 | 10篇 |
数学 | 53611篇 |
物理学 | 122500篇 |
出版年
2021年 | 1923篇 |
2020年 | 2227篇 |
2019年 | 2320篇 |
2018年 | 11128篇 |
2017年 | 11961篇 |
2016年 | 8491篇 |
2015年 | 4141篇 |
2014年 | 4706篇 |
2013年 | 13219篇 |
2012年 | 14490篇 |
2011年 | 24672篇 |
2010年 | 15351篇 |
2009年 | 15448篇 |
2008年 | 21963篇 |
2007年 | 25101篇 |
2006年 | 11748篇 |
2005年 | 17188篇 |
2004年 | 12924篇 |
2003年 | 11707篇 |
2002年 | 9657篇 |
2001年 | 10665篇 |
2000年 | 8131篇 |
1999年 | 6066篇 |
1998年 | 4453篇 |
1997年 | 4518篇 |
1996年 | 4524篇 |
1995年 | 4025篇 |
1994年 | 3892篇 |
1993年 | 3502篇 |
1992年 | 4232篇 |
1991年 | 4279篇 |
1990年 | 3927篇 |
1989年 | 3853篇 |
1988年 | 3896篇 |
1987年 | 3816篇 |
1986年 | 3554篇 |
1985年 | 4880篇 |
1984年 | 4889篇 |
1983年 | 3936篇 |
1982年 | 4114篇 |
1981年 | 3869篇 |
1980年 | 3789篇 |
1979年 | 4031篇 |
1978年 | 4212篇 |
1977年 | 4069篇 |
1976年 | 3952篇 |
1975年 | 3809篇 |
1974年 | 3704篇 |
1973年 | 3863篇 |
1972年 | 2356篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
992.
993.
We introduce a random perturbed version of the classical fidelity and we show that it converges with the same rate of decay
of correlations, but not uniformly in the noise. This makes the classical fidelity unstable in the zero-noise limit. 相似文献
994.
Formulas that include the contribution from dipole-distributed anomalous masses represented as layers distributed in height relative to the reference ellipsoid to the gravitational field in the quadratic approximation have been derived. The relationships between the expansion coefficients of some function and its square in terms of spherical functions have been established. The contribution from the relief masses and the density jump at the Mohorovicic discontinuity is used to illustrate the results. 相似文献
995.
996.
In this paper we describe the design and manufacture of an axial-torsion test specimen, and provide relationships needed when
conducting stress-strain characterization experiments with the specimen. The specimen is a short hollow cylinder of rubber
bonded between two steel mounting rings, in which simultaneous axial and shear strains are produced via independently controlled
axial and twist displacements. We present calculations for the strain-displacement and stress-load relationships, and strain
energy density. These relationships have been established and validated via a combination of analytical and experimental techniques,
and finite element analysis. We have investigated the extent and effects of strain and stress field non-uniformity in the
test specimen. The specimen design is sufficiently simple that a closed-form expression for the strain-displacement relationship
has been successfully developed. 相似文献
997.
The hyperfine constants for muonium in elemental and binary inorganic solids suggest formation of three different families
of defect centre, with distinct electronic structures. The overall range of values, spanning nearly five orders of magnitude,
and their correlation with host properties such as band gap and electron affinity, reveal a deep-to-shallow instability which
has profound implications for the electrical properties of hydrogen impurity in electronic materials, both semiconducting
and dielectric. 相似文献
998.
Jae-Yeon Lee Eugene Lubarsky Ben T. Zinn 《Proceedings of the Combustion Institute》2005,30(2):1757-1764
This paper describes an experimental investigation of the feasibility of using “slow” active control approaches, which “instantaneously” change liquid fuel spray properties, to suppress combustion instabilities. The objective of this control approach was to break up the feedback between the combustion process heat release and combustor pressure oscillations that drive the instability by changing the characteristics of the combustion process (e.g., the characteristic combustion time). To demonstrate the feasibility of such control, this study used a proprietary fuel injector (NanomiserTM), which can vary its fuel spray properties, to investigate the dependence of acoustics–combustion process coupling, i.e., the driving of combustion instabilities, upon the fuel spray properties. This study showed that by changing the spray characteristics it is possible to significantly damp combustion instabilities. Furthermore, using combustion zone chemiluminescence distributions, which were obtained by Abel’s deconvolution synchronized with measured acoustic data, it has been shown that the instabilities were mostly driven midway between the combustor centerline and wall, a short distance downstream from the flame holder, where the mean axial flow velocity is approximately zero in the vortex near the flame holder. The results of this study strongly suggest that a “slow” active control system that employs controllable fuel injectors could be effectively used to prevent the onset of detrimental combustion instabilities. 相似文献
999.
The Bekenstein–Hawking entropy of certain black holes can be computed microscopically in string theory by mapping the elusive
problem of counting microstates of a strongly gravitating black hole to the tractable problem of counting microstates of a
weakly coupled D-brane system, which has no event horizon, and indeed comfortably fits on the head of a pin. We show here
that, contrary to widely held beliefs, the entropy of spherically symmetric black holes can easily be dwarfed by that of stationary
multi-black-hole “molecules” of the same total charge and energy. Thus, the corresponding pin-sized D-brane systems do not
even approximately count the microstates of a single black hole, but rather those of a zoo of entropically dominant multicentered
configurations.
Fourth Award in the 2007 Essay Competition of the Gravity Research Foundation. 相似文献
1000.
The possibility of performing a quantitative analysis of vibrational states of nanocrystalline carbon has been explored by using the spectroscopic method of diffuse IR reflection. An expression derived from the Kubelka-Munk relation has been proposed and employed to investigate the effect of the original parameters of a sample (absorber concentration, sample dispersion, radiation frequency, scattering factors) on the characteristic features of IR spectra. The IR absorption bands observed in the diffuse reflection spectrum of pyrographite were assigned. 相似文献