全文获取类型
收费全文 | 17649篇 |
免费 | 2005篇 |
国内免费 | 1416篇 |
专业分类
化学 | 7100篇 |
晶体学 | 171篇 |
力学 | 436篇 |
综合类 | 97篇 |
数学 | 6491篇 |
物理学 | 6775篇 |
出版年
2024年 | 14篇 |
2023年 | 167篇 |
2022年 | 284篇 |
2021年 | 385篇 |
2020年 | 438篇 |
2019年 | 530篇 |
2018年 | 477篇 |
2017年 | 531篇 |
2016年 | 552篇 |
2015年 | 553篇 |
2014年 | 832篇 |
2013年 | 1171篇 |
2012年 | 953篇 |
2011年 | 1169篇 |
2010年 | 946篇 |
2009年 | 1247篇 |
2008年 | 1320篇 |
2007年 | 1214篇 |
2006年 | 1049篇 |
2005年 | 791篇 |
2004年 | 749篇 |
2003年 | 634篇 |
2002年 | 537篇 |
2001年 | 463篇 |
2000年 | 382篇 |
1999年 | 439篇 |
1998年 | 338篇 |
1997年 | 299篇 |
1996年 | 222篇 |
1995年 | 280篇 |
1994年 | 243篇 |
1993年 | 201篇 |
1992年 | 161篇 |
1991年 | 115篇 |
1990年 | 194篇 |
1989年 | 212篇 |
1988年 | 122篇 |
1987年 | 131篇 |
1986年 | 138篇 |
1985年 | 133篇 |
1984年 | 101篇 |
1983年 | 44篇 |
1982年 | 49篇 |
1981年 | 46篇 |
1980年 | 38篇 |
1979年 | 36篇 |
1978年 | 33篇 |
1977年 | 35篇 |
1976年 | 25篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
101.
Lin and Zhang (J. Roy. Statist. Soc. Ser. B 61 (1999) 381) proposed the generalized additive mixed model (GAMM) as a framework for analysis of correlated data, where normally distributed random effects are used to account for correlation in the data, and proposed to use double penalized quasi-likelihood (DPQL) to estimate the nonparametric functions in the model and marginal likelihood to estimate the smoothing parameters and variance components simultaneously. However, the normal distributional assumption for the random effects may not be realistic in many applications, and it is unclear how violation of this assumption affects ensuing inferences for GAMMs. For a particular class of GAMMs, we propose a conditional estimation procedure built on a conditional likelihood for the response given a sufficient statistic for the random effect, treating the random effect as a nuisance parameter, which thus should be robust to its distribution. In extensive simulation studies, we assess performance of this estimator under a range of conditions and use it as a basis for comparison to DPQL to evaluate the impact of violation of the normality assumption. The procedure is illustrated with application to data from the Multicenter AIDS Cohort Study (MACS). 相似文献
102.
The time delay experiment proposed by I.I. Shapiro in 1964 and conducted in the seventies was the most precise experiment
of general relativity until that time. Further experimentation has improved the accuracy level of both the time delay and
the light deflection experiments. A simulation model is proposed that involves only a simple mass and time transformation
factor involving velocity of light. The light deflection and the time delay experiments are numerically simulated using this
model that does not use the general relativistic equations. The computed values presented in this paper compare well with
recent levels of accuracy of their respective experimental results. 相似文献
103.
Depending on various assumptions on the energy scale of inflation and assuming a primordial power spectrum of a step‐like structure, we explore new possibilities for Primordial Black Holes (PBH) and Planck relics to contribute substantially to Cold Dark Matter in the Universe. A recently proposed possibility to produce Planck relics in four‐dimensional string gravity is considered in this framework. Possible experimental detection of PBHs through gravitational waves is also explored. We stress that inflation with a low energy scale, and also possibly when Planck relics are produced, leads unavoidably to relics originating from PBHs that are not effectively classical during their formation, rendering the usual formalism inadequate for them. 相似文献
104.
105.
The Hawking radiation of Dirac particles on the event horizon of a nonuniformly rectilinearly accelerating black hole is studied in this paper. First, we construct the symmetrized null tetrad from which the spin coefficients and Dirac equation are derived. Next, by proposing generalized tortoise coordinate transformation, the decoupling problem of the Dirac equation with nonzero rest mass is solved. Finally, by analytic continuation, the Hawking thermal spectrum formula of Dirac particle for nonuniformly rectilinearly accelerating black hole is obtained. 相似文献
106.
光强一定时饱和光电流随入射光频率的变化关系辨析 总被引:2,自引:0,他引:2
对光电效应实验中饱和光电流随入射光频率变化关系的几种谬误进行了辨析,给出了光强一定时饱和光电流随入射光频率变化的正确规律并作了解释。 相似文献
107.
N. S. Kazak E. G. Katranji I. A. Utkin A. A. Ryzhevich A. N. Khilo 《Journal of Applied Spectroscopy》2004,71(5):697-701
The phenomenon of self-diffraction of Bessel light beams (BLB) in a nonlinear liquid medium has been studied experimentally and theoretically for the first time. Diffraction maxima which do not correspond to integer orders for an induced periodic structure have been registered. It has been shown that the appearance of these maxima is due to the initial BLB modulation, which can be caused by the departure of the axicon refracting surface from the ideal conical surface, as well as by the imperfection of the form of the Gaussian beam incident on the axicon. 相似文献
108.
Fabiano Severo Rodembusch Ndya Pesce da Silveira Dimitrios Samios Leandra Franciscato Campo Valter Stefani 《Journal of Polymer Science.Polymer Physics》2003,41(4):341-350
The solution behavior of new copolymers of methyl methacrylate and benzazole dyes emitting fluorescence because of an intramolecular proton‐transfer mechanism in the electronically excited state has been investigated by static light scattering, fluorescence spectroscopy, ultraviolet–visible, and gel permeation chromatography. In the dilute regime, with tetrahydrofuran (THF) and chloroform as solvents, the copolymers behave as typical polydisperse linear chains in good solvents. The analysis of the osmotic modulus for concentrated solutions in THF (c ≥ 60 g L?1) indicates the existence of an interchain association mechanism. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 341–350, 2003 相似文献
109.
通过数值求解一维瞬态受激布里渊散射(SBS)声光耦合波方程,从理论上分析了泵浦激光参数及光学材料参数对SBS过程发生阈值的影响。以SBS过程中建立起来的应力场抗拉(压)强度和散射场的反射率为判据,分析了激光脉宽及作用区域长度对激光超声破坏材料效果的影响,探讨了短脉冲激光(约ns)引起的激光超声对材料的破坏机理;讨论了通过参数配置有效遏制SBS过程激光超声对光学材料的破坏问题。 相似文献
110.
The dependence of emission direction of fast electrons on the laser intensity has been investigated. The experimental results show that, at nonrelativistic laser intensities, the emission of fast electrons is mainly in the polarization plane. With the increase of the laser intensity, fast electrons emit towards the laser propagation direction from laser polarization direction. At relativistic laser intensities, fast electrons move away from the laser polarization plane, closely to the reflection direction of the incident laser beam. 相似文献