全文获取类型
收费全文 | 15222篇 |
免费 | 2238篇 |
国内免费 | 1582篇 |
专业分类
化学 | 7375篇 |
晶体学 | 135篇 |
力学 | 2879篇 |
综合类 | 105篇 |
数学 | 1776篇 |
物理学 | 6772篇 |
出版年
2024年 | 53篇 |
2023年 | 215篇 |
2022年 | 680篇 |
2021年 | 665篇 |
2020年 | 678篇 |
2019年 | 609篇 |
2018年 | 477篇 |
2017年 | 522篇 |
2016年 | 762篇 |
2015年 | 604篇 |
2014年 | 793篇 |
2013年 | 1472篇 |
2012年 | 808篇 |
2011年 | 853篇 |
2010年 | 771篇 |
2009年 | 896篇 |
2008年 | 922篇 |
2007年 | 971篇 |
2006年 | 855篇 |
2005年 | 684篇 |
2004年 | 533篇 |
2003年 | 529篇 |
2002年 | 472篇 |
2001年 | 402篇 |
2000年 | 397篇 |
1999年 | 331篇 |
1998年 | 330篇 |
1997年 | 261篇 |
1996年 | 227篇 |
1995年 | 208篇 |
1994年 | 203篇 |
1993年 | 154篇 |
1992年 | 114篇 |
1991年 | 93篇 |
1990年 | 73篇 |
1989年 | 63篇 |
1988年 | 47篇 |
1987年 | 49篇 |
1986年 | 32篇 |
1985年 | 37篇 |
1984年 | 30篇 |
1983年 | 18篇 |
1982年 | 34篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 23篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1957年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Within the large literature on inter-organizational networks, there has been some discussion of linking-pin organizations and the role they play in integrating these networks. Based on this verbal specification of linking-pin organizations, we construct operational criteria and empirical methods for identifying these structurally important organizations in potentially large and complex inter-organizational networks. These methods are based on ideas drawn from blockmodeling, structural holes, centrality and centralization of networks, and identifying cut-points in networks. These methods are applied to a constructed example and then to real empirical inter-organizational networks. Implications and contrasts with other methods are discussed, together with some open problems. 相似文献
22.
The sub-millisecond protonation dynamics of the chromophore in S65T mutant form of the green fluorescent protein (GFP) was
tracked after a rapid pH jump following laser-induced proton release from the caged photolabile compoundo-nitrobenzaldehyde. Following a jump in pH from 8 to 5 (which is achieved within 2 μs), the fluorescence of S65T GFP decreased
as a single exponential with a time constant of ∼90 μs. This decay is interpreted as the conversion of the deprotonated fluorescent
GFP chromophore to a protonated non-fluorescent species. The protonation kinetics showed dependence on the bulk viscosity
of the solvent, and therefore implicates bulk solvent-controlled protein dynamics in the protonation process. The protonation
is proposed to be a sequential process involving two steps: (a) proton transfer from solvent to the chromophore, and (b) internal
structural rearrangements to stabilize a protonated chromophore. The possible implications of these observations to protein
dynamics in general is discussed 相似文献
23.
In this article, we define stochastic dynamics for a system coupled to reservoirs. The rules for forward and backward transitions are related by a generalized detailed balance identity involving the system and its reservoirs. We compare the variation of information and of entropy. We define the Carnot dissipation and prove that it can be expressed in terms of cyclic transformations. Lower bounds for partial dissipations are also studied, as well as the effect of switching off certain reservoirs. We also study the near degeneracy of the stochastic matrix, relate it to phase transitions and we show that the reduced dynamics on the set of phases is a permutation. Finally, we relate these concepts to heat, work and more generally to the dissipation and creation of resources, in general systems. 相似文献
24.
25.
Numerical schemes for systems with multiple spatio-temporal scales are investigated. The multiscale schemes use asymptotic results for this type of systems which guarantee the existence of an effective dynamics for some suitably defined modes varying slowly on the largest scales. The multiscale schemes are analyzed in general, then illustrated on a specific example of a moderately large deterministic system displaying chaotic behavior due to Lorenz. Issues like consistency, accuracy, and efficiency are discussed in detail. The role of possible hidden slow variables as well as additional effects arising on the diffusive time-scale are also investigated. As a byproduct we obtain a rather complete characterization of the effective dynamics in Lorenz model. 相似文献
26.
J. Wang J. Kono A. Oiwa H. Munekata C. J. Stanton 《Superlattices and Microstructures》2003,34(3-6):563
We have carried out an ultrafast time-resolved differential reflectivity study of a ferromagnetic semiconductor InGaMnAs and made a systematic comparison with low-temperature grown and high-temperature grown InGaAs reference films. Very short carrier lifetimes (2 ps) were observed in InGaMnAs and the low-temperature grown InGaAs film, but not in the high-temperature grown InGaAs film. We attribute the short lifetimes to carrier trapping by mid-gap states introduced during low-temperature MBE growth. Furthermore, at long times, we observed periodic oscillations in the differential reflectivity signal with period 20 ps, which we interpret as coherent acoustic phonons. 相似文献
27.
To improve aircraft crash safety, conditions critical to occupants survival during a crash must be known. In view of the importance of this problem, studies of post-crash dynamic behavior of victims are necessary in order to reduce severe injuries. In this study, crash dynamics program SOM-LA/TA, incorporating a dynamic model of the human body with a finite element model of the seat structure was used. Modifications were performed in the program for reconstruction of an occupant's head impact with the interior walls or bulkhead. A viscoelastic-type contact force model was used to represent the compliance characteristics of the bulkhead. Correlated studies of analytical simulations with impact sled test results were accomplished. A parametric study of the coefficients in the contact force model was then performed in order to obtain the correlations between the coefficients and the Head Injury Criteria. A measure of optimal values for the bulkhead compliance and displacement requirements was thus achieved in order to keep the possibility of a head injury as little as possible. This information could in turn be used in the selection of suitable materials for the bulkhead, instrument panel, or interior walls of an aircraft. 相似文献
28.
The grain boundary is an interface and the surface tension is one of its important thermodynamic properties. In this paper,
the surface tension of the ∑9 grain boundary for α-Fe at various temperatures and pressures is calculated by means of Computer
Molecular Dynamics (CMD). The results agree satisfactorily with the experimental data. It is shown that the contribution of
entropy to surface tension of grain boundary can be ignored.
The project supported by the National Natural Science Foundation of China and the Science Foundation of Chinese Academy of
Sciences. 相似文献
29.
30.
For the NO molecule, modelled as a Morse oscillator, time-dependent (TD) nuclear Schr?dinger equation has been numerically
solved for the multiphoton vibrational dynamics of the molecule under a far-infrared laser of wavelength 10503 nm, and four
different intensities,I = 1 × 108, 1 × 1013, 5 × 1016, and 5 × 1018 W cm−2 respectively. Starting from the vibrational ground state at zero time, various TD quantities such as the norm, dissociation
probability, potential energy curve and dipole moment are examined. Rich high-harmonics generation (HHG) spectra and above-threshold
dissociation (ATD) spectra, due to the multiphoton interaction of vibrational motions with the laser field, and consequent
elevation to the vibrational continuum, have been obtained and analysed.
Dedicated to Professor C N R Rao on his 70th birthday
An erratum to this article is available at . 相似文献