全文获取类型
收费全文 | 25787篇 |
免费 | 5922篇 |
国内免费 | 4235篇 |
专业分类
化学 | 19512篇 |
晶体学 | 351篇 |
力学 | 372篇 |
综合类 | 175篇 |
数学 | 1014篇 |
物理学 | 14520篇 |
出版年
2024年 | 99篇 |
2023年 | 430篇 |
2022年 | 1010篇 |
2021年 | 1171篇 |
2020年 | 1369篇 |
2019年 | 1101篇 |
2018年 | 984篇 |
2017年 | 1054篇 |
2016年 | 1445篇 |
2015年 | 1335篇 |
2014年 | 1614篇 |
2013年 | 2575篇 |
2012年 | 1882篇 |
2011年 | 1982篇 |
2010年 | 1567篇 |
2009年 | 1622篇 |
2008年 | 1788篇 |
2007年 | 1781篇 |
2006年 | 1630篇 |
2005年 | 1479篇 |
2004年 | 1347篇 |
2003年 | 1132篇 |
2002年 | 1011篇 |
2001年 | 728篇 |
2000年 | 726篇 |
1999年 | 515篇 |
1998年 | 526篇 |
1997年 | 385篇 |
1996年 | 300篇 |
1995年 | 276篇 |
1994年 | 188篇 |
1993年 | 172篇 |
1992年 | 123篇 |
1991年 | 94篇 |
1990年 | 93篇 |
1989年 | 80篇 |
1988年 | 48篇 |
1987年 | 36篇 |
1986年 | 36篇 |
1985年 | 35篇 |
1984年 | 32篇 |
1983年 | 22篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1972年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 617 毫秒
61.
A. Khrennikov 《Annalen der Physik》2003,12(10):575-585
We study the probabilistic consequences of the choice of the basic number field in the quantum formalism. We demonstrate that by choosing a number field for a linear space representation of quantum model it is possible to describe various interference phenomena. We analyse interference of probabilistic alternatives induced by real, complex, hyperbolic (Clifford) and p‐adic representations. 相似文献
62.
63.
Liyue Liu Yingge Yang Yafei Zhang 《Physica E: Low-dimensional Systems and Nanostructures》2004,24(3-4):343-348
The electrical conductivity was investigated for multi-walled carbon nanotubes (MWNTs) dissolved in chloroform and toluene, respectively. The electrical conductivity remarkably increased with increase in the content of MWNTs, which is in accordance with Archie's equation . Furthermore, a hypothesis of the electronic transport process was proposed to explain the difference between the solution and the solid compound. In addition, the temperature dependence of the electrical conductivity shows that log σ vs. 1/T exist in a good linear relationship. The activation energy of the electrical conductivity decreased with increase in concentration and an inflexion was observed at 60 °C in MWNT/toluene solution. 相似文献
64.
1 INTRODUCTION Carbon nanotubes have many potential applica- tions due to their unique structures and properties[1~4]. Physicists have been studying their electrical, me- chanical and other properties since their discove- ries[5, 6]. Recently, chemists are interested in carbon nanotubes because their properties can be altered by chemical functionalization[7~14], and these functiona- lized nanotubes can undergo further chemical trea- tment. So the potential application range of such na- … 相似文献
65.
《Magnetic resonance in chemistry : MRC》2003,41(6):417-430
A systematic study of the one‐bond and long‐range J(C,C), J(C,H) and J(H,H) in the series of nine bicycloalkanes was performed at the SOPPA level with special emphasis on the coupling transmission mechanisms at bridgeheads. Many unknown couplings were predicted with high reliability. Further refinement of SOPPA computational scheme adjusted for better performance was carried out using bicyclo[1.1.1]pentane as a benchmark to investigate the influence of geometry, basis set and electronic correlation. The calculations performed demonstrated that classical ab initio SOPPA applied with the locally dense Dunning's sets augmented with inner core s‐functions used for coupled carbons and Sauer's sets augmented with tight s‐functions used for coupled hydrogens performs perfectly well in reproducing experimental values of different types of coupling constants (the estimated reliability is ca 1–2 Hz) in relatively large organic molecules of up to 11 carbon atoms. Additive coupling increments were derived for J(C,C), J(C,H) and J(H,H) based on the calculated values of coupling constants within SOPPA in the model bicycloalkanes, in reasonably good agreement with the known values obtained earlier on pure empirical grounds. Most of the bridgehead couplings in all but one bicycloalkane appeared to be essentially additive within ca 2–3 Hz while bicyclo[1.1.1]pentane demonstrated dramatic non‐additivity of ?14.5 Hz for J(C,C), +16.6 Hz for J(H,H) and ?5.5 Hz for J(C,H), in line with previous findings. Non‐additivity effects in the latter compound established at the SOPPA level should be attributed to the through‐space non‐bonded interactions at bridgeheads due to the essential overlapping of the bridgehead rear lobes which provides an additional and effective non‐bonding coupling path for the bridgehead carbons and their protons in the bicyclopentane framework. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
66.
M. Castagnino R. Id Betan R. Laura 《International Journal of Theoretical Physics》2003,42(10):2423-2439
By extending the notion of mixed states to functionals acting on the space of observables with diagonal singularity we obtain a well-defined complex spectral decomposition of the time evolution for a quantum decaying system. In this formalism, generalized Gamow states are obtained with well-defined physical properties. 相似文献
67.
Dimitar I. Pushkarov 《Central European Journal of Physics》2004,2(3):420-455
Basic ideas and results which characterize quantum diffusion of defects in quantum crystals like solid helium as a new phenomenon
are presented. Quantum effects in such media lead to a delocalization of point defects (vacancies, impurities etc.) and they
turn into quasiparticles of a new type—defectons, which are characterized not by their position in the crystal lattice but
by their quasimomentum and dispersion law. Defecton-defecton and defecton-phonon scattering are considered and an interpolation
formula for the diffusion coefficient valid in all interesting temperature and concentration regions is presented. A comparison
with the experimental data is made. Some alternative points of view are discussed in detail and the inconsistency of the Kisvarsanyi-Sullivan
theory is shown. 相似文献
68.
We consider a quark model based on QCD scale anomaly in which the quarks move in the field of an effective glueball field.
Hadrons correspond to solitonic bags of higher energy density in a nonperturbative sea of condensed gluons. We calculate the
static properties of nucleon in this model and find that the nucleon mass is far too large (2.4–4 GeV) and the proton charge
radius (0.37–0.54 fm) is low. The proton gyromagnetic ratio and gA/gv are in reasonable agreement with the experimental numbers. 相似文献
69.
We propose a unified method for deducing recursive relations for the canonical partition function of a system of noninteracting particles with charge conservation if the particles follow the Bose–Einstein, Fermi–Dirac, or Maxwell–Boltzmann statistics or parastatistics. For all these types of statistics, we find recursive relations for the partition function of a new statistical model of nuclear multifragmentation with electric charge and baryon number conservation, accounting for the internal degrees of freedom of the nuclear fragments. 相似文献
70.
Palladium-containing zeolites catalyze the cycloisomerization of diethyl diallylmalonate to dimethylcyclopentenes. When the reaction is carried out in toluene, the performance of the palladium catalyst depends on the pore size of the zeolites. At 60 °C, palladium adsorbed on large pore size Beta zeolite (pore size ∼7.4 Å) is more active than medium pore size ZSM-5 (pore size ∼5.4 Å). This lower activity of ZSM-5 compared to Beta is attributable to the restricted diffusion of reagent and products through the ZSM-5 channels as compared to Beta zeolite. However, due to the gas-like diffusion characteristic of the supercritical state, the activity of ZSM-5 increases and becomes identical to that of Beta zeolite using supercritical CO2 as medium. 相似文献