全文获取类型
收费全文 | 18243篇 |
免费 | 1557篇 |
国内免费 | 1148篇 |
专业分类
化学 | 9800篇 |
晶体学 | 93篇 |
力学 | 85篇 |
综合类 | 55篇 |
数学 | 8972篇 |
物理学 | 1943篇 |
出版年
2023年 | 303篇 |
2022年 | 216篇 |
2021年 | 239篇 |
2020年 | 464篇 |
2019年 | 555篇 |
2018年 | 561篇 |
2017年 | 369篇 |
2016年 | 544篇 |
2015年 | 675篇 |
2014年 | 931篇 |
2013年 | 1467篇 |
2012年 | 930篇 |
2011年 | 1192篇 |
2010年 | 1066篇 |
2009年 | 1158篇 |
2008年 | 1299篇 |
2007年 | 1267篇 |
2006年 | 1029篇 |
2005年 | 710篇 |
2004年 | 658篇 |
2003年 | 612篇 |
2002年 | 513篇 |
2001年 | 382篇 |
2000年 | 379篇 |
1999年 | 391篇 |
1998年 | 333篇 |
1997年 | 246篇 |
1996年 | 290篇 |
1995年 | 337篇 |
1994年 | 263篇 |
1993年 | 221篇 |
1992年 | 204篇 |
1991年 | 107篇 |
1990年 | 87篇 |
1989年 | 90篇 |
1988年 | 75篇 |
1987年 | 66篇 |
1986年 | 54篇 |
1985年 | 92篇 |
1984年 | 61篇 |
1983年 | 22篇 |
1982年 | 72篇 |
1981年 | 60篇 |
1980年 | 51篇 |
1979年 | 61篇 |
1978年 | 63篇 |
1977年 | 46篇 |
1976年 | 51篇 |
1975年 | 22篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
对不同的本底真空条件下,采用甚高频等离子体增强化学气相沉积技术沉积的氢化微晶硅(μc_Si∶H)薄膜中的氧污染问题进行了比较研究.对不同氧污染条件下制备的薄膜样品的x射线光电子能谱与傅里叶变换红外吸收光谱测量结果表明:μc_Si∶H薄膜中,氧以Si—O,O—O和O—H三种不同的键合模式存在,不同的键合模式源自不同的物理机理.μc_Si∶H薄膜的Raman光谱、电导率与激活能的测量结果进一步显示:沉积过程中氧污染程度的不同,对μc_Si∶H薄膜的结构特性与电学特性产生显著影响;而不同氧污染对μc_Si∶H薄膜电学特性的影响不同于氢化非晶硅(a_Si:H)薄膜.
关键词:
氢化微晶硅薄膜
甚高频等离子体增强化学气相沉积
氧污染 相似文献
102.
《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
103.
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
104.
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
105.
Matthew D. Horton 《Linear algebra and its applications》2007,425(1):130-142
After defining and exploring some of the properties of Ihara zeta functions of digraphs, we improve upon Kotani and Sunada’s bounds on the poles of Ihara zeta functions of undirected graphs by considering digraphs whose adjacency matrices are directed edge matrices. 相似文献
106.
Franc Forstnerič 《Mathematische Annalen》1992,292(1):163-180
107.
Summary.
This paper is concerned with a high order convergent
discretization for the semilinear reaction-diffusion problem:
,
for , subject to ,
where .
We assume that on
, which
guarantees uniqueness of a solution to
the problem. Asymptotic properties of
this solution are discussed. We consider a
polynomial-based three-point
difference scheme on a simple piecewise
equidistant mesh of Shishkin type.
Existence and local uniqueness of a solution
to the scheme are analysed. We
prove that the scheme is almost fourth order
accurate in the discrete maximum
norm, uniformly in the perturbation parameter
. We present numerical
results in support of this result.
Received February 25, 1994 相似文献
108.
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
109.
We generalize several results on bounded analytic interpolation of Fitzgerald and Horn, which work by majorization by positive
definite kernels, to the cases of several complex variables and operator-valued interpolation. Using a lemma of Kolmogorov,
we complement a simplification due to Szafraniec in the proofs of the theorems.
Received: November 21, 2006. Accepted: August 03, 2007. 相似文献
110.
Alexander G. Ramm Alexandra B. Smirnova Angelo Favini 《Annali di Matematica Pura ed Applicata》2003,182(1):37-52
A nonlinear operator equation F(x)=0, F:H→H, in a Hilbert space is considered. Continuous Newton’s-type procedures based on a construction of a dynamical system with
the trajectory starting at some initial point x
0 and becoming asymptotically close to a solution of F(x)=0 as t→+∞ are discussed. Well-posed and ill-posed problems are investigated.
Received: June 29, 2001; in final form: February 26, 2002?Published online: February 20, 2003
This paper was finished when AGR was visiting Institute for Theoretical Physics, University of Giessen. The author thanks
DAAD for support 相似文献