全文获取类型
收费全文 | 85106篇 |
免费 | 2468篇 |
国内免费 | 330篇 |
专业分类
化学 | 47748篇 |
晶体学 | 540篇 |
力学 | 3048篇 |
综合类 | 12篇 |
数学 | 17693篇 |
物理学 | 18863篇 |
出版年
2023年 | 450篇 |
2022年 | 432篇 |
2021年 | 699篇 |
2020年 | 873篇 |
2019年 | 848篇 |
2018年 | 2258篇 |
2017年 | 2323篇 |
2016年 | 2528篇 |
2015年 | 2237篇 |
2014年 | 2243篇 |
2013年 | 4176篇 |
2012年 | 6980篇 |
2011年 | 6364篇 |
2010年 | 4205篇 |
2009年 | 3500篇 |
2008年 | 4128篇 |
2007年 | 4105篇 |
2006年 | 3712篇 |
2005年 | 7212篇 |
2004年 | 6288篇 |
2003年 | 4249篇 |
2002年 | 2303篇 |
2001年 | 1300篇 |
2000年 | 957篇 |
1999年 | 805篇 |
1998年 | 592篇 |
1997年 | 519篇 |
1996年 | 604篇 |
1995年 | 413篇 |
1994年 | 452篇 |
1993年 | 438篇 |
1992年 | 586篇 |
1991年 | 537篇 |
1990年 | 490篇 |
1989年 | 451篇 |
1988年 | 382篇 |
1987年 | 340篇 |
1986年 | 317篇 |
1985年 | 478篇 |
1984年 | 439篇 |
1983年 | 295篇 |
1982年 | 395篇 |
1981年 | 368篇 |
1980年 | 301篇 |
1979年 | 309篇 |
1978年 | 288篇 |
1976年 | 356篇 |
1975年 | 288篇 |
1974年 | 299篇 |
1973年 | 295篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
In this Note, we present a result concerning the non existence of linear monotone schema with fixed stencil on regular meshes for some linear parabolic equation in two dimensions. The parabolic equations of interest arise from non isotropic diffusion modelling. A corollary is that no linear monotone 9 points-schemes can be designed for the one-dimensional heat equation emerged in the plane with an arbitrary direction of diffusion. Some applications of this result are provided: for the Fokker–Planck–Lorentz model for electrons in the context of plasma physics; all linear monotone scheme for the one-dimensional hyperbolic heat equation treated as a two-dimensional problem are not consistent in the diffusion limit for an arbitrary direction of propagation. We also examine the case of the Landau equation. To cite this article: C. Buet, S. Cordier, C. R. Acad. Sci. Paris, Ser. I 340 (2005). 相似文献
82.
Let Ψ(x,y) (resp. Ψm(x,y)) denote the number of integers not exceeding x that are y-friable, i.e. have no prime factor exceeding y (resp. and are coprime to m). Evaluating the ratio Ψm(x/d,y)/Ψ(x,y) for 1≤slantd≤slantx, m≥slant 1, x≥slant y≥slant 2, turns out to be a crucial step for estimating arithmetic sums over friable integers. Here, it is crucial to obtain formulae with a very wide range of validity. In this paper, several uniform estimates are provided for the aforementioned ratio, which supersede all previously known results. Applications are given to averages of various arithmetic functions over friable integers which in turn improve corresponding results from the literature. The technique employed rests mainly on the saddle-point method, which is an efficient and specific tool for the required design.2000 Mathematics Subject Classification: Primary—11N25; Secondary—11K65, 11N37 相似文献
83.
84.
We prove that the generalized random walks associated to a root system R in and a nonnegative multiplicity function k defined on R, converge in distribution (if suitably normalized) to a Markov process with càdlàg trajectories and infinitesimal generator a differential-difference operator on which generalizes the usual Laplacian. To cite this article: L. Gallardo, L. Godefroy, C. R. Acad. Sci. Paris, Ser. I 338 (2004). 相似文献
85.
86.
A tomographic reconstruction method based on Monte Carlo random searching guided by the information contained in the projections
of radiographed objects is presented. In order to solve the optimization problem, a multiscale algorithm is proposed to reduce
computation. The reconstruction is performed in a coarse-to-fine multigrid scale that initializes each resolution level with
the reconstruction of the previous coarser level, which substantially improves the performance. The method was applied to
a real case reconstructing the internal structure of a small metallic object with internal components, showing excellent results. 相似文献
87.
Abstract. We propose a general approach to deal with nonlinear, nonconvex variational problems based on a reformulation of the problem
resulting in an optimization problem with linear cost functional and convex constraints. As a first step we explicitly explore
these ideas to some one-dimensional variational problems and obtain specific conclusions of an analytical and numerical nature. 相似文献
88.
Ana Luísa Daniel‐da‐Silva João Carlos Moura Bordado José Miguel Martín‐Martínez 《Journal of Polymer Science.Polymer Physics》2007,45(22):3034-3045
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007 相似文献
89.
Could simple intraannular-arm macrocyclic systems exist in enantiopure stable forms? The effective synthesis of two representative compounds of such a class, their resolution into enantiomers, and experiments justifying their stability toward racemization are presented. 相似文献
90.
Monika Goikoetxea María J. Barandiaran José M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5838-5846
The mechanisms involved in the formation of n‐butanol during the synthesis of butyl acrylate containing latices were investigated. The experimental results showed that neither the hydrolysis of butyl acrylate nor of the ester bond in the butyl acrylate segments of the polymer played a major role in the formation of n‐butanol, which was mainly generated from the polymer backbone, by transfer reactions to polymer chain followed by cyclization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5838–5846, 2007 相似文献