全文获取类型
收费全文 | 26621篇 |
免费 | 814篇 |
国内免费 | 152篇 |
专业分类
化学 | 17054篇 |
晶体学 | 132篇 |
力学 | 685篇 |
综合类 | 2篇 |
数学 | 5173篇 |
物理学 | 4541篇 |
出版年
2023年 | 136篇 |
2022年 | 263篇 |
2021年 | 454篇 |
2020年 | 436篇 |
2019年 | 404篇 |
2018年 | 800篇 |
2017年 | 556篇 |
2016年 | 707篇 |
2015年 | 653篇 |
2014年 | 689篇 |
2013年 | 1456篇 |
2012年 | 1520篇 |
2011年 | 1636篇 |
2010年 | 1067篇 |
2009年 | 964篇 |
2008年 | 1509篇 |
2007年 | 1467篇 |
2006年 | 1372篇 |
2005年 | 1272篇 |
2004年 | 1075篇 |
2003年 | 969篇 |
2002年 | 845篇 |
2001年 | 476篇 |
2000年 | 516篇 |
1999年 | 348篇 |
1998年 | 306篇 |
1997年 | 279篇 |
1996年 | 349篇 |
1995年 | 231篇 |
1994年 | 247篇 |
1993年 | 244篇 |
1992年 | 225篇 |
1991年 | 174篇 |
1990年 | 220篇 |
1989年 | 181篇 |
1988年 | 162篇 |
1987年 | 148篇 |
1986年 | 146篇 |
1985年 | 198篇 |
1984年 | 245篇 |
1983年 | 160篇 |
1982年 | 201篇 |
1981年 | 201篇 |
1980年 | 196篇 |
1979年 | 155篇 |
1978年 | 190篇 |
1977年 | 167篇 |
1976年 | 174篇 |
1975年 | 134篇 |
1973年 | 122篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
G. Meillère 《Analytical and bioanalytical chemistry》1899,38(9-10):674-675
142.
Dávid Szegvári Romána Zelkó Péter Horváth András Gergely 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):169-172
Enantioselective solubility of rac-norgestrel was found in the presence of γ-cyclodextrin or hydroxypropyl-γ-cyclodextrin.
In both cases the efficacious enantiomer was dissolved in greater extent. Calculating the molar absorptivity and molar ellipticity
spectra of the γ- and hydroxypropyl-γ-cyclodextrin aqueous complexes, a simple and rapid direct circular dichroism (CD) spectrometric
method was obtained for the determination of the enantiomer ratio in aqueous solutions. 相似文献
143.
Enrique Bendito ngeles Carmona Andr s M. Encinas 《Applied Numerical Mathematics》2004,50(3-4):343-370
Our aim is to set the foundations of a discrete vectorial calculus on uniform n-dimensional grids, that can be easily reformulated on general irregular grids. As a key tool we first introduce the notion of tangent space to any grid node. Then we define the concepts of vector field, field of matrices and inner products on the space of grid functions and on the space of vector fields, mimicking the continuous setting. This allows us to obtain the discrete analogous of the basic first order differential operators, gradient and divergence, whose composition define the fundamental second order difference operator. As an application, we show that all difference schemes, with constant coefficients, for first and second order differential operators with constant coefficients can be seen as difference operators of the form
for suitable choices of q,
and
. In addition, we characterize special properties of the difference scheme, such as consistency, symmetry and positivity in terms of q,
and
. 相似文献
144.
Dominique Tourns 《Historia Mathematica》2003,30(4):457
In the period which precedes the appearance of computers, needs in calculation of the scientists and engineers led to an important development of graphic methods of integration. To contribute to the study of this little known phenomenon, the article presents techniques and instruments used for the graphic integration of ordinary differential equations, and looks for their historic origins by going back to the beginning of calculus: processes of geometric calculation by the polygonal method or the method of radius of curvature, use of tractional motion for the conception of integraphs, reduction to graphic quadratures in finite or infinite number. 相似文献
145.
146.
Inés CarrancoJosé Luis D?&#x;az Oscar JiménezRodolfo Lavilla 《Tetrahedron letters》2003,44(46):8449-8452
The Lewis acid-catalyzed interaction of dihydropyridines with ethyl glyoxalate and primary aliphatic amines yields, depending on the reaction conditions, bicyclic aminals or rearranged tetrahydropyridines in one-pot multicomponent reactions. 相似文献
147.
Quantization consists in studying the L
r
-error induced by the approximation of a random vector X by a vector (quantized version) taking a finite number n of values. We investigate this problem for Gaussian random vectors in an infinite dimensional Banach space and in particular, for Gaussian processes. A precise link proved by Fehringer(4) and Dereich et al.
(3) relates lower and upper bounds for small ball probabilities with upper and lower bounds for the quantization error, respectively. We establish a complete relationship by showing that the same holds for the direction from the quantization error to small ball probabilities. This allows us to compute the exact rate of convergence to zero of the minimal L
r
-quantization error from logarithmic small ball asymptotics and vice versa. 相似文献
148.
Michel Crouzeix 《Numerical Algorithms》2003,33(1-4):193-201
We consider the lumped mass method with piecewise linear finite elements in two dimensions. When the triangulation is of Delaunay type it is known that the discrete scheme satisfies a maximum principle. In this work we pursue the analysis and prove that the discrete semi-group is l
p
contractive in a sector, which implies smoothing effects and provide some resolvent estimates. 相似文献
149.
The aim of the paper is to investigate the limit behaviour of the least squares estimator of the shift parameter of nearly unstable, nearly stable, and nearly explosive AR(1) models. Both zero start and stationary cases are treated. Connection with the maximum likelihood estimator of the shift parameter of continuous time AR(1) processes is also discussed. 相似文献