全文获取类型
收费全文 | 412144篇 |
免费 | 2942篇 |
国内免费 | 802篇 |
专业分类
化学 | 199126篇 |
晶体学 | 6096篇 |
力学 | 22233篇 |
综合类 | 17篇 |
数学 | 57879篇 |
物理学 | 130537篇 |
出版年
2020年 | 2942篇 |
2019年 | 3491篇 |
2018年 | 11678篇 |
2017年 | 12231篇 |
2016年 | 10108篇 |
2015年 | 4269篇 |
2014年 | 6369篇 |
2013年 | 14225篇 |
2012年 | 14507篇 |
2011年 | 23292篇 |
2010年 | 15707篇 |
2009年 | 16037篇 |
2008年 | 21050篇 |
2007年 | 23856篇 |
2006年 | 11470篇 |
2005年 | 15309篇 |
2004年 | 11965篇 |
2003年 | 11208篇 |
2002年 | 9659篇 |
2001年 | 9402篇 |
2000年 | 7284篇 |
1999年 | 5432篇 |
1998年 | 4675篇 |
1997年 | 4644篇 |
1996年 | 4424篇 |
1995年 | 3987篇 |
1994年 | 4035篇 |
1993年 | 3794篇 |
1992年 | 4336篇 |
1991年 | 4544篇 |
1990年 | 4284篇 |
1989年 | 4339篇 |
1988年 | 4224篇 |
1987年 | 4171篇 |
1986年 | 3928篇 |
1985年 | 5064篇 |
1984年 | 5274篇 |
1983年 | 4388篇 |
1982年 | 4486篇 |
1981年 | 4349篇 |
1980年 | 4075篇 |
1979年 | 4569篇 |
1978年 | 4743篇 |
1977年 | 4695篇 |
1976年 | 4745篇 |
1975年 | 4474篇 |
1974年 | 4447篇 |
1973年 | 4586篇 |
1972年 | 3285篇 |
1971年 | 2979篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
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
952.
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
953.
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
954.
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
955.
V. V. Lozhkarev S. G. Garanin R. R. Gerke V. N. Ginzburg E. V. Katin A. V. Kirsanov G. A. Luchinin A. N. Mal’shakov M. A. Mart’yanov O. V. Palashov A. K. Poteomkin N. N. Rukavishnikov A. M. Sergeev S. A. Sukharev G. I. Freidman E. A. Khazanov A. V. Charukhchev A. A. Shaikin I. V. Yakovlev 《JETP Letters》2005,82(4):178-180
In experiments on the parametrical amplification of femtosecond pulses in wide-aperture DKDP crystals, a power of more than 100 TW has been reached, which is much higher than the record level achieved in such lasers. The energy efficiency obtained for the parametric amplifier is equal to 27%. The energy of a 72-fs pulse is equal to 10 J. 相似文献
956.
In recent years there has been considerable progress in the application of large-eddy simulation (LES) to increasingly complex flow configurations. Nevertheless a lot of fundamental problems still need to be solved in order to apply LES in a reliable way to real engineering problems, where typically finite-volume codes on unstructured meshes are used. A self-adaptive discretisation scheme, in the context of an unstructured finite-volume flow solver, is investigated in the case of isotropic turbulence at infinite Reynolds number. The Smagorinsky and dynamic Smagorinsky sub-grid scale models are considered. A discrete interpolation filter is used for the dynamic model. It is one of the first applications of a filter based on the approach presented by Marsden et al. In this work, an original procedure to impose the filter shape through a specific selection process of the basic filters is also proposed. Satisfactory results are obtained using the self-adaptive scheme for implicit LES. When the scheme is coupled with the sub-grid scale models, the numerical dissipation is shown to be dominant over the sub-grid scale component. Nevertheless the effect of the sub-grid scale models appears to be important and beneficial, improving in particular the energy spectra. A test on fully developed channel flow at Reτ = 395 is also performed, comparing the non-limited scheme with the self-adaptive scheme for implicit LES. Once again the introduction of the limiter proves to be beneficial. 相似文献
957.
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
958.
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
959.
M. Vedani G. Angella Paola Bassani D. Ripamonti A. Tuissi 《Journal of Thermal Analysis and Calorimetry》2007,87(1):277-284
Equal channel angular
pressing (ECAP) was carried out on solution annealed samples of Al–Mg–Si–Zr
and Al–Mg–Si–Zr–Sc alloys to achieve a substantial
grain refinement of the materials. Post ECAP aging was then investigated on
the ultrafine grained alloys by DSC and TEM analyses.
DSC scans
were carried out with heating rates ranging from 5 to 30°C min–1.
Peak identification was performed by the support of literature information
and TEM analyses. Precipitation kinetics revealed to be similar for both alloys
but the Sc-free alloy showed a recrystallization peak at temperatures ranging
from 310 to 340°C, depending on the strain accumulated during ECAP. On
the contrary, the Sc-containing alloy showed a greater grain stability. Analyses
of peak positions and of activation energies as a function of ECAP passes
experienced by the samples revealed large modifications of precipitation kinetics
in the ultrafine-grained alloys with respect to the coarse-grained materials. 相似文献
960.
Maxim V. Pavlov 《Communications in Mathematical Physics》2007,272(2):469-505
The algebro-geometric approach for integrability of semi-Hamiltonian hydrodynamic type systems is presented. The class of
symmetric hydrodynamic type systems is defined and the calculation of the associated Riemann surfaces is greatly simplified for this
class. Many interesting and physically motivated examples are investigated. 相似文献