全文获取类型
收费全文 | 34387篇 |
免费 | 617篇 |
国内免费 | 510篇 |
专业分类
化学 | 14559篇 |
晶体学 | 318篇 |
力学 | 1544篇 |
综合类 | 20篇 |
数学 | 9753篇 |
物理学 | 9320篇 |
出版年
2023年 | 59篇 |
2022年 | 70篇 |
2021年 | 165篇 |
2020年 | 172篇 |
2019年 | 184篇 |
2018年 | 1303篇 |
2017年 | 1567篇 |
2016年 | 925篇 |
2015年 | 763篇 |
2014年 | 731篇 |
2013年 | 1048篇 |
2012年 | 3561篇 |
2011年 | 2802篇 |
2010年 | 2082篇 |
2009年 | 1818篇 |
2008年 | 944篇 |
2007年 | 974篇 |
2006年 | 885篇 |
2005年 | 4705篇 |
2004年 | 4141篇 |
2003年 | 2506篇 |
2002年 | 661篇 |
2001年 | 404篇 |
2000年 | 204篇 |
1999年 | 247篇 |
1998年 | 183篇 |
1997年 | 134篇 |
1996年 | 121篇 |
1995年 | 84篇 |
1994年 | 104篇 |
1993年 | 83篇 |
1992年 | 203篇 |
1991年 | 189篇 |
1990年 | 150篇 |
1989年 | 137篇 |
1988年 | 118篇 |
1987年 | 73篇 |
1986年 | 67篇 |
1985年 | 65篇 |
1984年 | 52篇 |
1979年 | 40篇 |
1976年 | 84篇 |
1975年 | 45篇 |
1974年 | 44篇 |
1973年 | 55篇 |
1972年 | 43篇 |
1970年 | 37篇 |
1969年 | 40篇 |
1968年 | 39篇 |
1966年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
101.
Testing goodness of fit for the distribution of errors in multivariate linear models 总被引:2,自引:0,他引:2
M.D. Jimnez Gamero J. Muoz García R. Pino Mejías 《Journal of multivariate analysis》2005,95(2):301-322
In this paper, to test goodness of fit to any fixed distribution of errors in multivariate linear models, we consider a weighted integral of the squared modulus of the difference between the empirical characteristic function of the residuals and the characteristic function under the null hypothesis. We study the limiting behaviour of this test statistic under the null hypothesis and under alternatives. In the asymptotics, the rank of the design matrix is allowed to grow with the sample size. 相似文献
102.
Efficient synthesis of ferrocenylenones using a Friedel-Crafts acylation reaction is described. Acryloyl, methacryloyl, crotonoyl, cinnamoyl, and β-methylcrotonoyl chlorides react with ferrocene in the presence of a Lewis acid (EtAlCl2 or EtAlCl2-Me3Al) to give the corresponding ferrocenylenones (acryloyl, methacryloyl, crotonoyl, cinnamoyl, and methylcrotonoylferrocenes) in good isolated yields. Besides ferrocenylenones, chloroactylferrocene is also synthesised by this method. 相似文献
103.
Titanium tetrachloride promoted reaction of silyl ketene acetals with epoxides, followed by acidic work-up, affords butanolides in moderate/good yields. With epihalohydrins the reaction is regioselective and occurs at the less substituted end of the epoxide; the γ-haloalkyl-γ-butanolides thus obtained can be further transformed into various products. 相似文献
104.
The problem of homoaromaticity in mono-, di- and polyfluorinated- homotropylium cations is addressed by the B3LYP/6-311++G** DFT method. The energetic, structural and magnetic criteria are used for this purpose. They convincingly show that the ground state equilibrium species are aromatic, or in other words that the homoaromaticity is preserved by the (poly)fluorination. In contrast, a considerable decrease in the aromatic stabilization is observed in the transition structures (TS). According to the NICS(0) index, they vary form strongly antiaromatic, via weakly and non-aromatic to slightly aromatic transition states. However, the hierarchy of the aromaticity in fluorinated homotropylium ions predicted by NICS(0) is completely unrelated to that obtained by using the energy criterion assuming a kinetic definition of aromaticity. On the other hand the latter is closely related to geometric parameters of the equilibrium and transition structures. 相似文献
105.
In this work we show that the energy associated to the linear three-dimensional magneto-elastic system decays polynomially to zero as time goes to infinity, provided the initial data is smooth enough. 相似文献
106.
C. Torres O. Alejos C. de Francisco J.M. Muñoz P. Hernández-Gómez 《Applied Physics A: Materials Science & Processing》2003,77(3-4):543-547
This paper describes a robust and fast fitting procedure applicable for relaxing processes that cannot be understood as a discrete sum of single processes but require an activation energy distribution. The method is based on a set of closed-form expressions that allow the computation of the relaxation parameters directly from the isochronal curves obtained experimentally. The usefulness of this method is checked by analyzing the isochronal curves given by a theoretical energy distribution and the magnetic disaccommodation spectra observed in yttrium iron garnet (YIG) samples. PACS 02.60.Ed; 75.60.Lr; 75.50.Gg 相似文献
107.
Theoretical models for Monte Carlo simulation of radiative processes, i.e. bremsstrahlung and characteristic x-ray emission, are presented. Possible strategies for simulating electron transport are briefly described. For mechanisms involving energy loss and angular deflections, difficulties for strict implementation of accurate numerical differential cross sections still remain due to the strong correlations between these variables. Practical solutions for the case of inelastic collisions and bremsstrahlung emission are described. Comparisons of simulation results with experimental data for several problems of interest in electron probe microanalysis are presented. 相似文献
108.
109.
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
110.
Gravimetric measurements of thermodesorption of n-hexane and n-heptane were performed under quasi-equilibrium conditions. Differential thermodesorption profiles for ZSM-5 and ZSM-11 showed two peaks, but for Y zeolites, only one thermodesorption peak was observed. A model function, derived from the Langmiur adsorption model, was fitted to the experimental data, and the model parameters (the adsorption entropy and enthalpy) were estimated. The two-step desorption profiles observed for ZSM-5 and ZSM-11 were attributed to the commensurate freezing effect, i.e. a transition in the adsorbed phase resulting in ordering of the adsorbed molecules in the zeolite channels. The results observed for ZSM-11 indicate that the zigzag channels typical for ZSM-5 micropore system are not necessary for this transition to occur. 相似文献