全文获取类型
收费全文 | 27610篇 |
免费 | 2995篇 |
国内免费 | 3472篇 |
专业分类
化学 | 9827篇 |
晶体学 | 107篇 |
力学 | 2112篇 |
综合类 | 218篇 |
数学 | 10713篇 |
物理学 | 11100篇 |
出版年
2024年 | 84篇 |
2023年 | 277篇 |
2022年 | 615篇 |
2021年 | 683篇 |
2020年 | 828篇 |
2019年 | 794篇 |
2018年 | 784篇 |
2017年 | 866篇 |
2016年 | 1039篇 |
2015年 | 905篇 |
2014年 | 1345篇 |
2013年 | 2373篇 |
2012年 | 1436篇 |
2011年 | 1706篇 |
2010年 | 1344篇 |
2009年 | 1761篇 |
2008年 | 1801篇 |
2007年 | 1880篇 |
2006年 | 1539篇 |
2005年 | 1315篇 |
2004年 | 1051篇 |
2003年 | 1090篇 |
2002年 | 1034篇 |
2001年 | 832篇 |
2000年 | 823篇 |
1999年 | 716篇 |
1998年 | 633篇 |
1997年 | 488篇 |
1996年 | 354篇 |
1995年 | 341篇 |
1994年 | 292篇 |
1993年 | 264篇 |
1992年 | 251篇 |
1991年 | 220篇 |
1990年 | 217篇 |
1989年 | 213篇 |
1988年 | 188篇 |
1987年 | 183篇 |
1986年 | 153篇 |
1985年 | 171篇 |
1984年 | 156篇 |
1983年 | 98篇 |
1982年 | 127篇 |
1981年 | 111篇 |
1980年 | 102篇 |
1979年 | 117篇 |
1978年 | 84篇 |
1977年 | 87篇 |
1976年 | 75篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
基于事前评价过程和自然界生物进化过程的相似性,提出了系统结构、系统结构模式和系统环境模式矩阵的概念,并根据系统结构、系统结构模式与系统环境模式矩阵的适应程度,建立了模式评价决策模型,制定了评价系统的评价分类准则,并对评价系统作了一定的理论分析.将此模型和方法应用于城市生态安全评价中,通过与模糊综合评价法的比较,表明了该评价模型和方法的优越性. 相似文献
92.
Magnetic properties of Co chain-coated carbon nanotube (CNT) were investigated using a first-principles calculation. Binding energy between Co chain and CNT increased with the coverage ratio, and the adsorption of Co chains on CNT enhanced the conductance channel. Total magnetic moment of Co chains coated on CNT increased with the coverage ratio, while the magnetic moment per Co atom decreased due to spin flip of majority spin states in Co atoms. Spin polarization at the Fermi level of the Co chains was calculated to converge to that of bulk fcc Co. 相似文献
93.
WU Ke ZHAO Weizhong & GUO Hanying Department of Mathematics Capital Normal University Beijing China Institute of Theoretical Physics Chinese Academy of Sciences Beijing China 《中国科学A辑(英文版)》2006,(11)
In a way similar to the continuous case formally, we define in different but equivalent manners the difference discrete connection and curvature on discrete vector bundle over the regular lattice as base space. We deal with the difference operators as the discrete counterparts of the derivatives based upon the differential calculus on the lattice. One of the definitions can be extended to the case over the random lattice. We also discuss the relation between our approach and the lattice gauge theory and apply to the discrete integrable systems. 相似文献
94.
The plastic deformation field near the horizontal surface of a half space of perfectly plastic material associated with an indenting rotating rigid tooth is studied using slip line theory. The tooth is one of many on a roll surface and indents first into the half-space material and then rotates about the roll center. A slip line field is proposed for the deforming plastic region and a solution scheme is outlined. The emphasis is on determining the shape of the deforming region, especially that of the free surface. The study has a potential application in roughness transfer in metal forming processing. 相似文献
95.
E. Mathieu Y. Foucher P. Dellamonica J. P. Daures 《Methodology and Computing in Applied Probability》2007,9(3):389-397
In AIDS control, physicians have a growing need to use pragmatically useful and interpretable tools in their daily medical
taking care of patients. Semi-Markov process seems to be well adapted to model the evolution of HIV-1 infected patients. In
this study, we introduce and define a non homogeneous semi-Markov (NHSM) model in continuous time. Then the problem of finding
the equations that describe the biological evolution of patient is studied and the interval transition probabilities are computed.
A parametric approach is used and the maximum likelihood estimators of the process are given. A Monte Carlo algorithm is presented
for realizing non homogeneous semi-Markov trajectories. As results, interval transition probabilities are computed for distinct
times and follow-up has an impact on the evolution of patients.
相似文献
96.
The phase boundary theory and the contact rule of phase regions are compared, and some weaknesses of the latter are manifested.
The comparison between the Gupta’s method and the boundary theory method for constructing multicomponent isobaric sections
is also presented. 相似文献
97.
Tony Donnelly 《Applied Surface Science》2006,252(13):4445-4448
Ultra-thin (0.5-5 nm) films of Ag have been prepared by pulsed laser deposition in vacuum using a 26 ns KrF excimer laser at 1 J cm−2. The deposition was controlled using a Langmuir ion probe and a quartz crystal thickness monitor. Transmission electron microscopy showed that the films are not continuous, but are structured on nanometer size scales. Optical absorption spectra showed the expected surface plasmon resonance feature, which shifted to longer wavelength and increased in strength as the equivalent film thickness was increased. It is shown that Maxwell Garnett effective medium theory can be used to calculate the main features of optical absorption spectra. 相似文献
98.
We introduce the time-consistency concept that is inspired by the so-called “principle of optimality” of dynamic programming
and demonstrate – via an example – that the conditional value-at-risk (CVaR) need not be time-consistent in a multi-stage
case. Then, we give the formulation of the target-percentile risk measure which is time-consistent and hence more suitable
in the multi-stage investment context. Finally, we also generalize the value-at-risk and CVaR to multi-stage risk measures
based on the theory and structure of the target-percentile risk measure. 相似文献
99.
In this paper, an adaptive FE analysis is presented based on error estimation, adaptive mesh refinement and data transfer for enriched plasticity continua in the modelling of strain localization. As the classical continuum models suffer from pathological mesh-dependence in the strain softening models, the governing equations are regularized by adding rotational degrees-of-freedom to the conventional degrees-of-freedom. Adaptive strategy using element elongation is applied to compute the distribution of required element size using the estimated error distribution. Once a new mesh is generated, state variables and history-dependent variables are mapped from the old finite element mesh to the new one. In order to transfer the history-dependent variables from the old to new mesh, the values of internal variables available at Gauss point are first projected at nodes of old mesh, then the values of the old nodes are transferred to the nodes of new mesh and finally, the values at Gauss points of new elements are determined with respect to nodal values of the new mesh. Finally, the efficiency of the proposed model and computational algorithms is demonstrated by several numerical examples. 相似文献
100.
The Efficient Determination Criterion (EDC) generalizes the AIC and BIC criteria and provides a class of consistent estimators
for the order of a Markov chain with finite state space. In this note, we derive rates of convergence for the EDC estimates.
*Partially supported by CNPq, CAPES/PROCAD, FAPDF/PRONEX, FINATEC and FUNPE/UnB.
**Partially supported by CAPES. 相似文献