全文获取类型
收费全文 | 17893篇 |
免费 | 1884篇 |
国内免费 | 1520篇 |
专业分类
化学 | 10028篇 |
晶体学 | 100篇 |
力学 | 725篇 |
综合类 | 159篇 |
数学 | 8206篇 |
物理学 | 2079篇 |
出版年
2024年 | 38篇 |
2023年 | 350篇 |
2022年 | 284篇 |
2021年 | 295篇 |
2020年 | 560篇 |
2019年 | 575篇 |
2018年 | 591篇 |
2017年 | 453篇 |
2016年 | 669篇 |
2015年 | 747篇 |
2014年 | 1048篇 |
2013年 | 1583篇 |
2012年 | 970篇 |
2011年 | 1169篇 |
2010年 | 977篇 |
2009年 | 1121篇 |
2008年 | 1215篇 |
2007年 | 1160篇 |
2006年 | 966篇 |
2005年 | 758篇 |
2004年 | 702篇 |
2003年 | 687篇 |
2002年 | 595篇 |
2001年 | 424篇 |
2000年 | 413篇 |
1999年 | 398篇 |
1998年 | 352篇 |
1997年 | 242篇 |
1996年 | 249篇 |
1995年 | 260篇 |
1994年 | 232篇 |
1993年 | 155篇 |
1992年 | 167篇 |
1991年 | 92篇 |
1990年 | 84篇 |
1989年 | 74篇 |
1988年 | 66篇 |
1987年 | 44篇 |
1986年 | 42篇 |
1985年 | 65篇 |
1984年 | 62篇 |
1983年 | 20篇 |
1982年 | 65篇 |
1981年 | 46篇 |
1980年 | 35篇 |
1979年 | 39篇 |
1978年 | 40篇 |
1977年 | 28篇 |
1976年 | 30篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
《Solid State Communications》2003,127(11):703-706
In this work we present temperature dependent infrared reflectivity and absorption of Sr2FeWO6 between 700 and 17 K measured from 40 to 10000 cm−1. The reflectivity spectra show well defined phonon bands peaking at 143, 227, 377 and 625 cm−1 assigned to overlapping vibrational modes split from those active in cubic perovskite. We have also verified that this compound is structurally stable in the whole temperature range and that its optical gap at ∼750 cm−1 (95 meV) undergoes only a minor high temperature decrease ascribed to new thermally accessible levels. 相似文献
62.
In this paper, we study the linearization of the Cauchy problem and the mixed problem for the system of Grad--Hermite moments in nonequilibrium thermodynamics in the neighborhood of the equilibrium state. Stability conditions for solutions of the Cauchy problem are proved as a generalization of the classical Hermite--Biller theorem on stable polynomials. For the mixed problem, we prove an analog of the Vishik--Lyusternik theorem on small singular perturbations of general elliptic problems. The last observation allows us to introduce the Shapiro--Lopatinskii condition, which implies the well-posedness of the mixed problem. 相似文献
63.
F-H实验仪与光栅光谱仪连用观测253.7nm谱线 总被引:1,自引:0,他引:1
通过F-H实验仪和光栅光谱仪的连用,可实时观测汞原子从6s6s1So态激发到6s6sSP1态,退激时,辐射出能量为4.9eV的光量子,其波长为253.7nm. 相似文献
64.
Benson真有效意义下集值优化的广义最优性条件 总被引:12,自引:0,他引:12
本文引入了关于集值映射的α-阶Clarke切导数、α-阶邻接切导数及α-阶 伴随切导数的概念,借此建立了约束向量集值优化Benson真有效解导数型的Kuhn- Tucker条件. 相似文献
65.
《Magnetic resonance in chemistry : MRC》2003,41(9):731-734
An NMR study of one new and several known abietane diterpenes isolated from the roots of Aegiphila lhotzkyana is described. In addition to 1D NMR, several 2D shift‐correlated NMR pulse sequences (1H–1H‐COSY, NOESY, HMQC and HMBC) were used to establish all the structures, and unambiguously perform the 1H and 13C chemical shift assignments of the new natural diterpene and three derivatives, the NMR data for which have not been reported previously. Revision of current data assignment for teuvincenone H is also suggested. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
66.
One of the open questions in the geometry of line arrangements is to what extent does the incidence lattice of an arrangement determine its fundamental group. Line arrangements of up to 6 lines were recently classified by K.M. Fan (Michigan Math. J. 44(2) (1997) 283), and it turns out that the incidence lattice of such arrangements determines the projective fundamental group. We use actions on the set of wiring diagrams, introduced in (Garber et al. (J. Knot Theory Ramf.), to classify real arrangements of up to 8 lines. In particular, we show that the incidence lattice of such arrangements determines both the affine and the projective fundamental groups. 相似文献
67.
Parameters of Gaussian multivariate models are often estimated using the maximum likelihood approach. In spite of its merits, this methodology is not practical when the sample size is very large, as, for example, in the case of massive georeferenced data sets. In this paper, we study the asymptotic properties of the estimators that minimize three alternatives to the likelihood function, designed to increase the computational efficiency. This is achieved by applying the information sandwich technique to expansions of the pseudo-likelihood functions as quadratic forms of independent normal random variables. Theoretical calculations are given for a first-order autoregressive time series and then extended to a two-dimensional autoregressive process on a lattice. We compare the efficiency of the three estimators to that of the maximum likelihood estimator as well as among themselves, using numerical calculations of the theoretical results and simulations. 相似文献
68.
A robust and efficient adaptive reweighted estimator of multivariate location and scatter 总被引:1,自引:0,他引:1
Daniel Gervini 《Journal of multivariate analysis》2003,84(1):116-144
This article proposes a reweighted estimator of multivariate location and scatter, with weights adaptively computed from the data. Its breakdown point and asymptotic behavior under elliptical distributions are established. This adaptive estimator is able to attain simultaneously the maximum possible breakdown point for affine equivariant estimators and full asymptotic efficiency at the multivariate normal distribution. For the special case of hard-rejection weights and the MCD as initial estimator, it is shown to be more efficient than its non-adaptive counterpart for a broad range of heavy-tailed elliptical distributions. A Monte Carlo study shows that the adaptive estimator is as robust as its non-adaptive relative for several types of bias-inducing contaminations, while it is remarkably more efficient under normality for sample sizes as small as 200. 相似文献
69.
Noureddine Igbida 《Journal of Mathematical Analysis and Applications》2007,335(2):1061-1078
In this paper, we study the nonlinear evolution equation of Hele-Shaw type with dynamical boundary conditions. That is, the equation ut=Δw+f where u∈H(w) and H is the Heaviside function, with boundary condition μ(x,w)t∂w+k∇w⋅ν=g, where ν denotes the outward normal vector of the fixed boundary of the domain. We prove existence, uniqueness and some qualitative properties of the solution. 相似文献
70.
V. G. Lakhtin V. L. Ryabkov A. V. Kisin V. M. Nosova M. V. Polyakova E. A. Chernyshev 《Russian Chemical Bulletin》1995,44(11):2163-2167
Liquid-phase chlorination of a number of chloro(chlorovinyl)methylsilanes was investigated. A number of novelC-chlorosilanes were characterized by IR and1H NMR spectra. Some regularities of these reactions were determined; correlations between the structure of chloro(chlorovinyl)methylsilanes and their reactivities were identified.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2256–2260, November, 1995. 相似文献