全文获取类型
收费全文 | 127196篇 |
免费 | 2028篇 |
国内免费 | 443篇 |
专业分类
化学 | 56234篇 |
晶体学 | 1015篇 |
力学 | 8183篇 |
数学 | 38945篇 |
物理学 | 25290篇 |
出版年
2023年 | 384篇 |
2022年 | 323篇 |
2021年 | 539篇 |
2020年 | 705篇 |
2019年 | 679篇 |
2018年 | 11091篇 |
2017年 | 10754篇 |
2016年 | 7429篇 |
2015年 | 2272篇 |
2014年 | 1743篇 |
2013年 | 3351篇 |
2012年 | 7168篇 |
2011年 | 13669篇 |
2010年 | 7594篇 |
2009年 | 7626篇 |
2008年 | 9403篇 |
2007年 | 11477篇 |
2006年 | 2952篇 |
2005年 | 3929篇 |
2004年 | 3771篇 |
2003年 | 3762篇 |
2002年 | 2574篇 |
2001年 | 1205篇 |
2000年 | 1089篇 |
1999年 | 717篇 |
1998年 | 618篇 |
1997年 | 540篇 |
1996年 | 687篇 |
1995年 | 432篇 |
1994年 | 454篇 |
1993年 | 462篇 |
1992年 | 456篇 |
1991年 | 407篇 |
1990年 | 379篇 |
1989年 | 382篇 |
1988年 | 325篇 |
1987年 | 327篇 |
1986年 | 290篇 |
1985年 | 453篇 |
1984年 | 408篇 |
1983年 | 299篇 |
1982年 | 387篇 |
1981年 | 375篇 |
1980年 | 339篇 |
1979年 | 327篇 |
1978年 | 300篇 |
1976年 | 299篇 |
1975年 | 272篇 |
1974年 | 277篇 |
1973年 | 285篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
We have quantized a flat cosmological model in the context of the metric models, using the causal Bohmian quantum theory. The equations are solved and then we have obtained how the quantum corrections
influence the classical equations. 相似文献
952.
Vimla Vyas 《Pramana》2008,70(4):731-738
Speeds of sound and densities of three ternary liquid systems namely, toluene + n-heptane + n-hexane (I), cyclohexane + n-heptane + n-hexane (II) and n-hexane + n-heptane + n-decane (III) have been measured as a function of the composition at 298.15 K at atmospheric pressure. The experimental isothermal
compressibility has been evaluated from measured values of speeds of sound and density. The isothermal compressibility of
these mixtures has also been computed theoretically using different models for hard sphere equations of state and Flory’s
statistical theory. Computed values of isothermal compressibility have been compared with experimental findings. A satisfactory
agreement has been observed. The superiority of Flory’s statistical theory has been established quite reasonably over hard
sphere models.
相似文献
953.
The phase diagram of the coupled sine circle map system exhibits a variety of interesting phenomena including spreading regions
with spatiotemporal intermittency, non-spreading regions with spatial intermittency, and coherent structures termed solitons.
A spreading to non-spreading transition is seen in the system. A cellular automaton version of the coupled system maps the
spreading to non-spreading transition to a transition from a probabilistic to a deterministic cellular automaton. The solitonic
sector of the system shows spatiotemporal intermittency with soliton creation, propagation and absorption. A probabilistic
cellular automaton mapping is set up for this sector which can identify each one of these phenomena.
相似文献
954.
Note on Generalized Quantum Gates and Quantum Operations 总被引:1,自引:0,他引:1
Yue-Qing Wang Hong-Ke Du Yan-Ni Dou 《International Journal of Theoretical Physics》2008,47(9):2268-2278
Recently, Gudder proved that the set of all generalized quantum gates coincides the set of all contractions in a finite-dimensional
Hilbert space (S. Gudder, Int. J. Theor. Phys. 47:268–279, 2008). In this note, we proved that the set of all generalized
quantum gates is a proper subset of the set of all contractions on an infinite dimensional separable Hilbert space ℋ. Meanwhile,
we proved that the quantum operation deduced by an isometry is an extreme point of the set of all quantum operations on ℋ.
This subject is supported by NSF of China (10571113). 相似文献
955.
G. A. Martínez-Castañón N. Niño-Martínez F. Martínez-Gutierrez J. R. Martínez-Mendoza Facundo Ruiz 《Journal of nanoparticle research》2008,10(8):1343-1348
Silver nanoparticles with different sizes (7, 29, and 89 nm mean values) were synthesized using gallic acid in an aqueous
chemical reduction method. The nanoparticles were characterized using transmission electron microscopy (TEM), dynamic light
scattering (DLS), X-ray diffraction (XRD), and ultraviolet–visible (UV–Vis) absorption spectroscopy; the antibacterial activity
was assessed using the standard microdilution method, determining the minimum inhibitory concentration (MIC) according to
the National Committee for Clinical Laboratory Standards. From the microscopies studies (TEM) we observed that silver nanoparticles
have spherical (7 and 29 nm) and pseudospherical shape (89 nm) with a narrow size distribution. The sizes of the silver nanoparticles
were controlled by varying some experimental conditions. It was found that the antibacterial activity of the nanoparticles
varies when their size diminishes. 相似文献
956.
Bruno Galvan 《Journal of statistical physics》2008,131(6):1155-1167
An extension of the Born rule, the quantum typicality rule, has recently been proposed [B. Galvan in Found. Phys. 37:1540–1562 (2007)]. Roughly speaking, this rule states that if the
wave function of a particle is split into non-overlapping wave packets, the particle stays approximately inside the support
of one of the wave packets, without jumping to the others.
In this paper a formal definition of this rule is given in terms of imprecise probability. An imprecise probability space is a measurable space
endowed with a set of probability measures ℘. The quantum formalism and the quantum typicality rule allow us to define a set of probabilities
on (X
T
,ℱ), where X is the configuration space of a quantum system, T is a time interval and ℱ is the σ-algebra generated by the cylinder sets. Thus, it is proposed that a quantum system can be represented as the imprecise stochastic process
, which is a canonical stochastic process in which the single probability measure is replaced by a set of measures. It is
argued that this mathematical model, when used to represent macroscopic systems, has sufficient predictive power to explain
both the results of the statistical experiments and the quasi-classical structure of the macroscopic evolution. 相似文献
957.
Nicolas Dupré Julie Oliveri Jeremy Degryse Jean-Frédéric Martin Dominique Guyomard 《Ionics》2008,14(3):203-207
The growth and evolution of the interphase, due to contact with the ambient atmosphere or electrolyte, are followed using 7Li magic-angle spinning nuclear magnetic resonance (MAS NMR) in the case of two materials amongst the most promising candidates for positive electrodes for lithium batteries: LiFePO4 and LiMn0.5Ni0.5O2. The use of appropriate experimental conditions to acquire the NMR signal allows observing only the «diamagnetic» lithium species at the surface of the grains of active material. The reaction of LiMn0.5Ni0.5O2 with the ambient atmosphere or LiPF6 (1 M in Ethylene Carbonated/DiMéthyl Carbonate (EC/DMC)) electrolyte is extremely fast and leads to an important amount of lithium-containing diamagnetic species compared to what can be observed in the case of LiFePO4. The two studied materials display a completely different surface chemistry in terms of reactivity and/or kinetics of the surface towards electrolyte. Moreover, these results show that MAS NMR is a very promising tool to monitor phenomena taking place at the interface between electrode and electrolyte. 相似文献
958.
Wen-Yang Chang Te-Hua Fang Yu-Cheng Lin 《Applied Physics A: Materials Science & Processing》2008,92(3):693-701
Physical characteristics of polyimide films, including optical, micro/nano mechanical, and thermophysical characteristics
were investigated using a photometric, a nanoindentation, and a thermomechanical analyzer for applications in flexible sensors.
Experimental results show that UV light cannot transmit into the polyimide films. The transmittances, with a maximum of about
86%, at VIS and near IR lights decrease with increasing PI film thicknesses. The mechanical characteristics were determined
using tensile, bending moment, and nanoindentation testing. The stress–strain curve approximated bilinear characteristics,
the load–unload bending moment exhibited hysteresis, and nanoindentation generated elastic energy dissipation in the loading–unloading
region. Nanoindentation showed an almost uniform hardness and a reduced Young’s modulus of about 0.181±0.03 and 3.21±0.06 GPa,
respectively, when the penetrating depth was more than about 2 μm. Thermophysical characteristics were greatly influenced
on 8.3 and 25 μm specimens due to the higher relaxation of thin PI films. The thermal expansion remained steady when the thickness
was over 50 μm. The results show that PI films have potential in flexible sensing and higher temperature fabrication. 相似文献
959.
Yoav Linzon Boris A. Malomed Michael Zaezjev Roberto Morandotti Maite Volatier Vincent Aimez Richard Ares Shimshon Bar-Ad 《Central European Journal of Physics》2008,6(3):555-562
We study nonlinear interactions between discrete optical solitons that propagate in different regimes of diffraction, and
the nonlinear scattering of dispersive waves by local optical potentials. It is well known in optics that when linear coherent
waves meet, they interfere without interactions. Linear waves also scatter through local optical structures not exchanging
any power with the guided modes of these structures. As a focusing Kerr nonlinearity is present, such linearly-inhibited phenomena
can exist. Our studies are performed in silica and AlGaAs nonlinear waveguides, excited by ultra-short pulses in the near
infrared.
Presented at 9-th International Workshop on Nonlinear Optics Applications, NOA 2007, May 17–20, 2007, Świnoujście, Poland 相似文献
960.
A. A. Morozov Z. Geretovszky L. Égerházi T. Szörényi 《Applied Physics A: Materials Science & Processing》2008,93(3):691-696
A simple analytical model for inverse pulsed laser deposition is proposed. In the model the motion of the evaporated material
is assumed to emerge as from a point source located above the surface of evaporation at some distance. The obtained thickness
profiles of inverse deposited films agree well with those calculated by the test particle Monte Carlo method. The proposed
approach has been applied for analysis of experimental data on inverse pulsed laser deposition of graphite in nitrogen atmosphere
with nanosecond pulses of laser fluences between 1 and 7 J/cm2. The model describes well the thickness profiles and pressure dependence of film growth rate for inverse deposition. 相似文献