全文获取类型
收费全文 | 3252篇 |
免费 | 134篇 |
国内免费 | 1篇 |
专业分类
化学 | 2274篇 |
晶体学 | 19篇 |
力学 | 45篇 |
数学 | 443篇 |
物理学 | 606篇 |
出版年
2023年 | 26篇 |
2022年 | 10篇 |
2021年 | 40篇 |
2020年 | 50篇 |
2019年 | 30篇 |
2018年 | 66篇 |
2017年 | 59篇 |
2016年 | 109篇 |
2015年 | 110篇 |
2014年 | 116篇 |
2013年 | 231篇 |
2012年 | 235篇 |
2011年 | 267篇 |
2010年 | 120篇 |
2009年 | 119篇 |
2008年 | 198篇 |
2007年 | 201篇 |
2006年 | 166篇 |
2005年 | 168篇 |
2004年 | 149篇 |
2003年 | 126篇 |
2002年 | 105篇 |
2001年 | 84篇 |
2000年 | 89篇 |
1999年 | 52篇 |
1998年 | 23篇 |
1997年 | 28篇 |
1996年 | 62篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 31篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 7篇 |
1986年 | 15篇 |
1985年 | 21篇 |
1984年 | 18篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 15篇 |
1978年 | 13篇 |
1977年 | 8篇 |
1976年 | 12篇 |
1974年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有3387条查询结果,搜索用时 15 毫秒
61.
S. González-Pérez I. R. Martín F. Lahoz P. Haro-González J. Herreros 《Applied Physics A: Materials Science & Processing》2008,93(4):983-986
Local crystalline formation in erbium doped oxyfluoride glass has been obtained under a cw Argon laser irradiation up to 1.8
W pumping power. By exciting at 514 nm, the emission from 800 nm and 850 nm corresponding to the 4S3/2(2H11/2)→4I13/2 electronic transitions have been analyzed both inside and outside the irradiated area. The changes in the emission spectra
indicate that the high power Ar laser irradiation has resulted in a localized desvitrification process. The temperature dependence
of the fluorescence intensity ratio of the 800 nm and 850 nm emission bands has been used to determine the temperature of
the irradiated zone. Moreover, the average lifetime of the 4S3/2(2H11/2) thermalized levels have been measured as a function of the excitation spot position. An important decrease is observed at
the irradiated area. These results confirm that a localized cristalline phase has been created by the laser action. 相似文献
62.
63.
Ortega P. G. Rodríguez Montejo M. Valera M. Sánchez González J. J. López 《Structural chemistry》2019,30(6):2245-2255
Structural Chemistry - We have performed a systematic conformational analysis focused on the evaluation of the anomeric effect (AE) in a series of pyranose derivatives containing carbon, silicon,... 相似文献
64.
A multivariate calibration method was applied to improve the accuracy of the determination of cadmium in the presence of potassium by total reflection X-ray fluorescence (TXRF). Due to TXRF's relatively low resolution, a particular interference caused by potassium at line Kα 3.31 keV as interference can compromise the cadmium determination at line Lα 3.13 keV, respectively. The method is based on the hypothesis that the application of a multivariate calibration method, for example, partial least squares, could reduce variations due to interference and, consequently, improve the selectivity and accuracy in Cd determination. In this work, this strategy was evaluated on the X-ray fluorescence emission signals between 2.50 and 3.90 keV for a set of 26 different synthetic calibration mixtures and eight different mixtures for external calibration. Based on a certified reference material (Clay 2—CRM051) with high potassium levels, a significant improvement of accuracy for cadmium determination was observed, overcoming the problems associated with spectral interferences by potassium. 相似文献
65.
The oxidation of Fe(110) by O2 and H2O vapour has been studied by AES and LEED at room temperature in well ordered and in Ar bombarded surfaces. Ion irradiation causes in both cases an enhancement of the rate of oxidation. For O2 adsorption, it has been found that ion bombardment increases the rate of surface oxide growth, whereas in the case of H2O adsorption, the effect of the irradiation consists in facilitating the penetration of oxygen into the crystal bulk. 相似文献
66.
Kerdock codes (Kerdock, Inform Control 20:182–187, 1972) are a well-known family of non-linear binary codes with good parameters
admitting a linear presentation in terms of codes over the ring (see Nechaev, Diskret Mat 1:123–139, 1989; Hammons et al., IEEE Trans Inform Theory 40:301–319, 1994). These codes have been
generalized in different directions: in Calderbank et al. (Proc Lond Math Soc 75:436–480, 1997) a symplectic construction
of non-linear binary codes with the same parameters of the Kerdock codes has been given. Such codes are not necessarily equivalent.
On the other hand, in Kuzmin and Nechaev (Russ Math Surv 49(5), 1994) the authors give a family of non-linear codes over the
finite field F of q = 2
l
elements, all of them admitting a linear presentation over the Galois Ring R of cardinality q
2 and characteristic 22. The aim of this article is to merge both approaches, obtaining in this way new families of non-linear codes over F that can be presented as linear codes over the Galois Ring R. The construction uses symplectic spreads.
相似文献
67.
F. A. Gómez González 《代数通讯》2013,41(7):2867-2886
An analogue of the Wedderburn Principal Theorem (WPT) is considered for finite-dimensional Jordan superalgebras 𝔍 with solvable radical 𝒩, 𝒩 2 = 0, and such that , where 𝔽 is a field of characteristic zero. It is proved that the WPT is valid under some restrictions over the irreducible -bimodules contained in 𝒩, and it is shown with counterexamples that these restrictions cannot be weakened. 相似文献
68.
Eduardo González-Olivares Héctor Meneses-Alcay Betsabé González-Yañez Jaime Mena-Lorca Alejandro Rojas-Palma Rodrigo Ramos-Jiliberto 《Nonlinear Analysis: Real World Applications》2011,12(6):2931-2942
In this work, a bidimensional differential equation system obtained by modifying the well-known predator–prey Rosenzweig–MacArthur model is analyzed by considering prey growth influenced by the Allee effect.One of the main consequences of this modification is a separatrix curve that appears in the phase plane, dividing the behavior of the trajectories. The results show that the equilibrium in the origin is an attractor for any set of parameters. The unique positive equilibrium, when it exists, can be either an attractor or a repeller surrounded by a limit cycle, whose uniqueness is established by calculating the Lyapunov quantities. Therefore, both populations could either reach deterministic extinction or long-term deterministic coexistence.The existence of a heteroclinic curve is also proved. When this curve is broken by changing parameter values, then the origin turns out to be an attractor for all orbits in the phase plane. This implies that there are plausible conditions where both populations can go to extinction. We conclude that strong and weak Allee effects on prey population exert similar influences on the predator–prey model, thereby increasing the risk of ecological extinction. 相似文献
69.
Potential games are noncooperative games for which there exist auxiliary functions, called potentials, such that the maximizers of the potential are also Nash equilibria of the corresponding game. Some properties of Nash equilibria, such as existence or stability, can be derived from the potential, whenever it exists. We survey different classes of potential games in the static and dynamic cases, with a finite number of players, as well as in population games where a continuum of players is allowed. Likewise, theoretical concepts and applications are discussed by means of illustrative examples. 相似文献
70.
Francisco Durango José L. Fernández Pablo Fernández María J. González 《Israel Journal of Mathematics》2016,214(2):983-994
Any (measurable) function K from Rn to R defines an operator K acting on random variables X by K(X) = K(X1,..., Xn), where the Xj are independent copies of X. The main result of this paper concerns continuous selectors H, continuous functions defined in Rn and such that H(x1, x2,..., xn) ∈ {x1, x2,..., xn}. For each such continuous selector H (except for projections onto a single coordinate) there is a unique point ωH in the interval (0, 1) so that, for any random variable X, the iterates H(N) acting on X converge in distribution as N → ∞ to the ωH-quantile of X. 相似文献