全文获取类型
收费全文 | 41387篇 |
免费 | 428篇 |
国内免费 | 349篇 |
专业分类
化学 | 19189篇 |
晶体学 | 381篇 |
力学 | 1637篇 |
综合类 | 12篇 |
数学 | 10572篇 |
物理学 | 10373篇 |
出版年
2022年 | 84篇 |
2021年 | 145篇 |
2020年 | 182篇 |
2019年 | 172篇 |
2018年 | 1302篇 |
2017年 | 1553篇 |
2016年 | 934篇 |
2015年 | 773篇 |
2014年 | 756篇 |
2013年 | 1203篇 |
2012年 | 3790篇 |
2011年 | 3189篇 |
2010年 | 2242篇 |
2009年 | 1890篇 |
2008年 | 1362篇 |
2007年 | 1441篇 |
2006年 | 1437篇 |
2005年 | 5246篇 |
2004年 | 4645篇 |
2003年 | 2880篇 |
2002年 | 1073篇 |
2001年 | 471篇 |
2000年 | 256篇 |
1999年 | 309篇 |
1998年 | 274篇 |
1997年 | 250篇 |
1996年 | 239篇 |
1995年 | 174篇 |
1994年 | 192篇 |
1993年 | 172篇 |
1992年 | 288篇 |
1991年 | 257篇 |
1990年 | 210篇 |
1989年 | 180篇 |
1988年 | 185篇 |
1987年 | 133篇 |
1986年 | 108篇 |
1985年 | 161篇 |
1984年 | 135篇 |
1983年 | 105篇 |
1982年 | 111篇 |
1981年 | 121篇 |
1980年 | 120篇 |
1979年 | 114篇 |
1978年 | 103篇 |
1977年 | 81篇 |
1976年 | 143篇 |
1975年 | 108篇 |
1974年 | 90篇 |
1973年 | 111篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
61.
Ewa Stró?yna 《Journal of Differential Equations》2003,193(1):239-259
We solve completely the problem of classification of germs of complex planar vector fields with nilpotent singularity with respect to formal orbital equivalence. 相似文献
62.
Jean-Pierre Changeux Alain Connes M. B. DeBevoise Jean Petitot Mark Anspach 《Mathematical Intelligencer》2005,27(4):48-56
Conclusion The debate between Jean-Pierre Changeux and Alain Connes is one of the most, interesting to take place in recent years. It
re-frames in a very up-to-date context a whole series of traditional and difficult questions from the standpoint of the knowledge
and experience of two of the leading protagonists of contemporary science. To the choice presented by the neurobiologist between
a Platonist ontology and a neurocognitive psychology of mathematical activity, the mathematician replies with a conception
that is objective (neither ontological nor psychological) of the thoroughly consistent universe of mathematical idealities.
It is indeed in this three-sided arena that the major difficulties play themselves out. One of the great virtues of the book
is to cast a spotlight on this confrontation. 相似文献
63.
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
64.
In this paper, by using elementary analysis, we establish some new Lyapunov-type inequalities for nonlinear systems of differential equations, special cases of which contain the well-known equations such as Emden-Fowler-type and half-linear equations. The inequalities obtained here can be used as handy tools in the study of qualitative behaviour of solutions of the associated equations. 相似文献
65.
66.
It is well known from work of Bruhat and Tits that an affinebuilding has a spherical building at infinity. The paper studiesthe structure at infinity for an affine twin building. It isshown that the twinning restricts the structure at infinityin a natural way, producing two smaller spherical buildingsthat are canonically isomorphic to one another. In the processit is shown that to each wall and panel of these buildings atinfinity is attached a twin tree. 相似文献
67.
Stefan Pitsch Sebastian Wendeborn Ramanarayanan Krishnamurthy Armin Holzner Mark Minton Martin Bolli Christian Miculca Norbert Windhab Ronald Micura Michael Stanek Bernhard Jaun Albert Eschenmoser 《Helvetica chimica acta》2003,86(12):4270-4363
Pyranosyl‐RNA (‘p‐RNA’ ) is an oligonucleotide system isomeric to natural RNA and composed of the very same building blocks as RNA. Its generational, chemical, and informational properties are deemed to be those of an alternative nucleic acid system that could have been a candidate in Nature's evolutionary choice of the molecular basis of genetic function. We consider the study of the chemistry of p‐RNA as etiologically relevant in the sense that knowledge of its structural, chemical, and informational properties on the chemical level offers both a perspective and reference points for the recognition of specific structural assets of the RNA structure that made it the (supposedly) superior system among possible alternatives and, therefore, the system that became part of biology as we know it today. The paper describes the chemical synthesis of β‐d‐ (and L )‐ribopyranosyl‐(4′→2′)‐oligonucleotide sequences, presents a resume of their structural and chemical properties, and cautiously discusses what we may and may not have learned from the pyranosyl isomer of RNA with respect to the conundrum of RNA's origin. 相似文献
68.
E. Beinrohr M. Németh P. Tsch?pel G. T?lg 《Fresenius' Journal of Analytical Chemistry》1992,344(3):93-99
Summary Flow-through electrochemical cells with porous working electrodes made of crushed reticulated vitreous carbon and plated with mercury were used for absolute analysis of trace amounts of lead by anodic stripping coulometry with collection (ASCWC) in a flow system. The role of mercury coating, flow rate and pH were investigated. The coulombic content of the collection peak corresponded to the theoretical values calculated by Faraday's law in a concentration range from about 10–9 to 10–6 mol/l. The relative error and the relative standard deviation was +0.15% and 0.8%, respectively for 2×10–6 mol/l analyte concentration. The absolute detection limit (3 s) was 0.1 ng of Pb, the linear response range 7×104.
One leave from: Department of Analytical Chemistry, Slovak Technical University, CS-812 37 Bratislava, Czechoslovakia 相似文献
69.
Motivated by the central limit problem for convex bodies, we study normal approximation of linear functionals of high-dimensional
random vectors with various types of symmetries. In particular, we obtain results for distributions which are coordinatewise
symmetric, uniform in a regular simplex, or spherically symmetric. Our proofs are based on Stein’s method of exchangeable
pairs; as far as we know, this approach has not previously been used in convex geometry. The spherically symmetric case is
treated by a variation of Stein’s method which is adapted for continuous symmetries.
This work was done while at Stanford University. 相似文献
70.
Celik Tarimci Anda? Karamustafa Kutalmi? Güven Mehmet Kabak Akgül Ye?ilada 《Analytical sciences》2003,19(9):1347-1348
The crystal structure of 1-[3-(3,4-dimethoxyphenyl)-2-propenoyl]pyrrolidine (C15H19NO3) (I) has been determined by X-ray analysis. It crystallizes orthorhombic space group Pbca with a = 24.295(3), b = 15.086(3), c = 7.552(3)A, V = 2768(1)A3, Z = 8, Dcalc = 1.254 g/cm3, mu = (Mo K(alpha)) = 0.87 cm(-1). The title compound has analgesic activity of cycloaliphatic amine part. The molecule is deviated from planar configuration. 相似文献