全文获取类型
收费全文 | 322029篇 |
免费 | 3097篇 |
国内免费 | 849篇 |
专业分类
化学 | 176516篇 |
晶体学 | 5540篇 |
力学 | 13281篇 |
综合类 | 14篇 |
数学 | 31816篇 |
物理学 | 98808篇 |
出版年
2020年 | 2734篇 |
2019年 | 2979篇 |
2018年 | 3624篇 |
2017年 | 3760篇 |
2016年 | 5651篇 |
2015年 | 3514篇 |
2014年 | 5520篇 |
2013年 | 14105篇 |
2012年 | 10633篇 |
2011年 | 12954篇 |
2010年 | 9135篇 |
2009年 | 9142篇 |
2008年 | 11910篇 |
2007年 | 11580篇 |
2006年 | 11124篇 |
2005年 | 10079篇 |
2004年 | 9127篇 |
2003年 | 8444篇 |
2002年 | 8131篇 |
2001年 | 10337篇 |
2000年 | 7628篇 |
1999年 | 5894篇 |
1998年 | 4446篇 |
1997年 | 4524篇 |
1996年 | 4316篇 |
1995年 | 4011篇 |
1994年 | 3866篇 |
1993年 | 3597篇 |
1992年 | 4521篇 |
1991年 | 4540篇 |
1990年 | 4331篇 |
1989年 | 4327篇 |
1988年 | 4317篇 |
1987年 | 4327篇 |
1986年 | 4053篇 |
1985年 | 5171篇 |
1984年 | 5248篇 |
1983年 | 4157篇 |
1982年 | 4300篇 |
1981年 | 4212篇 |
1980年 | 3980篇 |
1979年 | 4498篇 |
1978年 | 4574篇 |
1977年 | 4629篇 |
1976年 | 4425篇 |
1975年 | 4087篇 |
1974年 | 4026篇 |
1973年 | 4034篇 |
1972年 | 2749篇 |
1968年 | 2454篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Copper bromide was used as a catalyst for the addition of pyrroles to enones. When both the reactants were used in equimolar amounts, mono and dialkylated products were obtained. However, the use of excess enone furnished only dialkylated products. Thus, copper bromide was shown to be an efficient catalyst for the dialkylation of pyrroles. 相似文献
103.
L. T. Ashchepkov 《Computational Mathematics and Mathematical Physics》2006,46(7):1168-1175
A general nonlinear programming problem with interval functions is considered. Two reductions of this problem to the deterministic nonlinear programming problem are proposed, and illustrative examples are discussed. 相似文献
104.
Nonlinear Theory of Spectra of Thermally Stimulated Currents in Complex Crystals with Hydrogen Bonds
Tonkonogov M. P. Ismailov Zh. T. Timokhin V. M. Fazylov K. K. Kalitka V. A. Baimukhanov Z. K. 《Russian Physics Journal》2002,45(10):1008-1018
The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field. 相似文献
105.
G. Tiana M.H. Jensen K. Sneppen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):135-140
A feedback mechanism that involves the proteins p53 and mdm2, induces cell death as a controlled response to severe DNA damage.
A minimal model for this mechanism demonstrates that the response may be dynamic and connected with the time needed to translate
the mdm2 protein. The response takes place if the dissociation constant k between p53 and mdm2 varies from its normal value. Although it is widely believed that it is an increase in k that triggers the response, we show that the experimental behaviour is better described by a decrease in the dissociation
constant. The response is quite robust upon changes in the parameters of the system, as required by any control mechanism,
except for few weak points, which could be connected with the onset of cancer.
Received 8 May 2002 / Received in final form 9 July 2002 Published online 17 September 2002 相似文献
106.
The equilibrium geometry and hyperfine interaction constants of the nearest and next-to-nearest neighbor atoms are calculated for a negatively charged silicon vacancy in the high-spin state in cubic SiC. The calculations are performed within the cluster approach in terms of the density-functional theory (DFT). It is shown that the results of calculations with the use of a 70-atom cluster are in good agreement with experimental data. A detailed consideration is given to spin polarization in the electron subsystem and the applicability of a simple LCAO model that is commonly used in the interpretation of the electron paramagnetic resonance data for semiconductors. The spin density distribution for the defect under investigation is analyzed in terms of localized orbitals. 相似文献
107.
108.
James K. Freericks Elliott H. Lieb Daniel Ueltschi 《Communications in Mathematical Physics》2002,227(2):243-279
The Falicov–Kimball model is a simple quantum lattice model that describes light and heavy electrons interacting with an
on-site repulsion; alternatively, it is a model of itinerant electrons and fixed nuclei. It can be seen as a simplification
of the Hubbard model; by neglecting the kinetic (hopping) energy of the spin up particles, one gets the Falicov–Kimball model.
We show that away from half-filling, i.e. if the sum of the densities of both kinds of particles differs from 1, the particles
segregate at zero temperature and for large enough repulsion. In the language of the Hubbard model, this means creating two
regions with a positive and a negative magnetization.
Our key mathematical results are lower and upper bounds for the sum of the lowest eigenvalues of the discrete Laplace operator
in an arbitrary domain, with Dirichlet boundary conditions. The lower bound consists of a bulk term, independent of the shape
of the domain, and of a term proportional to the boundary. Therefore, one lowers the kinetic energy of the itinerant particles
by choosing a domain with a small boundary. For the Falicov- Kimball model, this corresponds to having a single “compact”
domain that has no heavy particles.
Received: 21 June 2001 / Accepted: 4 January 2002 相似文献
109.
A.R. DegheidyM.T. Attia M. Sallah 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,74(3):285-297
The time-independent radiative transfer problem in a scattering and absorbing planar random medium with general boundary conditions and internal energy source is considered. The medium is assumed to consist of two randomly mixed immiscible fluids, with the mixing statistics described as a two-state homogeneous Markov process. The problem is solved in terms of the solution of the corresponding free-source problem with simple boundary conditions which is solved using Pomraning-Eddington approximation in the deterministic case. A formalism, developed to treat radiative transfer in statistical mixtures, is used to obtain the ensemble-averaged solution. The average partial heat fluxes are calculated in terms of the albedoes of the source-free problem. Results are obtained for isotropic and anisotropic scattering for specular and diffused reflecting boundaries. 相似文献
110.