全文获取类型
收费全文 | 147215篇 |
免费 | 10235篇 |
国内免费 | 22007篇 |
专业分类
化学 | 121611篇 |
晶体学 | 3006篇 |
力学 | 3157篇 |
综合类 | 1355篇 |
数学 | 16337篇 |
物理学 | 33991篇 |
出版年
2024年 | 288篇 |
2023年 | 1657篇 |
2022年 | 3722篇 |
2021年 | 3604篇 |
2020年 | 4071篇 |
2019年 | 4753篇 |
2018年 | 3443篇 |
2017年 | 5312篇 |
2016年 | 4913篇 |
2015年 | 4204篇 |
2014年 | 5708篇 |
2013年 | 11419篇 |
2012年 | 9535篇 |
2011年 | 8708篇 |
2010年 | 7318篇 |
2009年 | 9295篇 |
2008年 | 9511篇 |
2007年 | 9861篇 |
2006年 | 9012篇 |
2005年 | 7765篇 |
2004年 | 7288篇 |
2003年 | 6009篇 |
2002年 | 6860篇 |
2001年 | 4476篇 |
2000年 | 4751篇 |
1999年 | 4050篇 |
1998年 | 3637篇 |
1997年 | 2613篇 |
1996年 | 2249篇 |
1995年 | 2093篇 |
1994年 | 1796篇 |
1993年 | 1483篇 |
1992年 | 1372篇 |
1991年 | 982篇 |
1990年 | 771篇 |
1989年 | 724篇 |
1988年 | 567篇 |
1987年 | 425篇 |
1986年 | 369篇 |
1985年 | 360篇 |
1984年 | 336篇 |
1983年 | 181篇 |
1982年 | 279篇 |
1981年 | 280篇 |
1980年 | 265篇 |
1979年 | 272篇 |
1978年 | 231篇 |
1977年 | 174篇 |
1976年 | 141篇 |
1973年 | 97篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
Summary. We generalise and apply a refinement indicator of the type originally designed by Mackenzie, Süli and Warnecke in [15] and
[16] for linear Friedrichs systems to the Euler equations of inviscid, compressible fluid flow. The Euler equations are symmetrized
by means of entropy variables and locally linearized about a constant state to obtain a symmetric hyperbolic system to which
an a posteriori error analysis of the type introduced in [15] can be applied. We discuss the details of the implementation of the refinement
indicator into the DLR--Code which is based on a finite volume method of box type on an unstructured grid and present numerical results.
Received May 15, 1995 / Revised version received April 17, 1996 相似文献
73.
Levoglucosenone reacts with α-aminoazoles to yield azolo[1,5-a]pyrimidine systems fused with a carbohydrate fragment. The reaction oocurs much more smoothly than in the case of other α,β-unsaturated
ketones. The reactions of levoglucosenone with β-dicarbonyl compounds (dimedone, barbituric acid) in the presence of a base
results in the pyran ring closure, which has never been observed earlier in reactions of β-dicarbonyl compounds with α,β-unsaturated
ketones under the conditions of basic catalysis. The structures of products were established by IR and NMR spectroscopy.
For Part 3, see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 553–558, March, 1997. 相似文献
74.
75.
Summary. Let be a square matrix dependent on parameters and , of which we choose as the eigenvalue parameter. Many computational problems are equivalent to finding a point such that has a multiple eigenvalue at . An incomplete decomposition of a matrix dependent on several parameters is proposed. Based on the developed theory two new algorithms are
presented for computing multiple eigenvalues of with geometric multiplicity . A third algorithm is designed for the computation of multiple eigenvalues with geometric multiplicity but which also appears to have local quadratic convergence to semi-simple eigenvalues. Convergence analyses of these methods
are given. Several numerical examples are presented which illustrate the behaviour and applications of our methods.
Received December 19, 1994 / Revised version received January 18, 1996 相似文献
76.
Addition of functionalized zinc-copper reagents to the title complexes proceeds in a highly diastereoselective fashion to afford dienol complexes. The relative configurations of adducts 3d were determined by single X-ray diffraction analysis. 相似文献
77.
Double Michael additions of lithium enolaie of 1,4-dioxaspiro[4.5]dec-6-en-8-one to four acrylates afforded bicyclo[2.2.2]octan-2-ones with high regio- and stereoselectivities in moderate yields. 相似文献
78.
The characterization of the clusters formed on alkaline hydrolysis of [PdCl4]2– was performed using17O,23Na,35Cl,133Cs NMR and UV spectroscopy. The chemical composition of the clusters was found to be [Pd(OH)2]
n
·nNaCl. No mononuclear oxo- or hydroxocomplexes were detected. The spatial structure of the clusters is stabilized by alkali metal cations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 675–679, April, 1993. 相似文献
79.
The dependence of the beam propagation factor (M
2 parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively
studied. Our investigations show that the M
2 parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due
to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration
associated with the thermal lens induced by the pump beam. Such dependency of M
2 parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd3+ -doped GdVO4 crystal and the values of α and β parameters were estimated from the experimentally measured data points. 相似文献
80.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data. 相似文献