全文获取类型
收费全文 | 314326篇 |
免费 | 3753篇 |
国内免费 | 1091篇 |
专业分类
化学 | 170607篇 |
晶体学 | 4457篇 |
力学 | 13029篇 |
综合类 | 7篇 |
数学 | 36262篇 |
物理学 | 94808篇 |
出版年
2020年 | 1983篇 |
2019年 | 1954篇 |
2018年 | 1965篇 |
2017年 | 1875篇 |
2016年 | 3858篇 |
2015年 | 3235篇 |
2014年 | 4422篇 |
2013年 | 13976篇 |
2012年 | 10728篇 |
2011年 | 13363篇 |
2010年 | 8270篇 |
2009年 | 8255篇 |
2008年 | 12335篇 |
2007年 | 12571篇 |
2006年 | 12212篇 |
2005年 | 11154篇 |
2004年 | 10034篇 |
2003年 | 8848篇 |
2002年 | 8700篇 |
2001年 | 10109篇 |
2000年 | 7710篇 |
1999年 | 6115篇 |
1998年 | 4894篇 |
1997年 | 4733篇 |
1996年 | 4773篇 |
1995年 | 4363篇 |
1994年 | 4114篇 |
1993年 | 3940篇 |
1992年 | 4431篇 |
1991年 | 4293篇 |
1990年 | 4011篇 |
1989年 | 3830篇 |
1988年 | 4120篇 |
1987年 | 3784篇 |
1986年 | 3677篇 |
1985年 | 5317篇 |
1984年 | 5395篇 |
1983年 | 4377篇 |
1982年 | 4753篇 |
1981年 | 4793篇 |
1980年 | 4545篇 |
1979年 | 4663篇 |
1978年 | 4665篇 |
1977年 | 4644篇 |
1976年 | 4597篇 |
1975年 | 4508篇 |
1974年 | 4356篇 |
1973年 | 4524篇 |
1972年 | 2569篇 |
1971年 | 1879篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
941.
942.
K. J. Bayer 《Fresenius' Journal of Analytical Chemistry》1885,24(1):542-546
Ohne ZusammenfassungSt. Petersburg, den 20. April 1885. 相似文献
943.
The kinetics of C6H5 reactions with n‐CnH2n+2 (n = 3, 4, 6, 8) have been studied by the pulsed laser photolysis/mass spectrometric method using C6H5COCH3 as the phenyl precursor at temperatures between 494 and 1051 K. The rate constants were determined by kinetic modeling of the absolute yields of C6H6 at each temperature. Another major product C6H5CH3 formed by the recombination of C6H5 and CH3 could also be quantitatively modeled using the known rate constant for the reaction. A weighted least‐squares analysis of the four sets of data gave k (C3H8) = (1.96 ± 0.15) × 1011 exp[?(1938 ± 56)/T], and k (n‐C4H10) = (2.65 ± 0.23) × 1011 exp[?(1950 ± 55)/T] k (n‐C6H14) = (4.56 ± 0.21) × 1011 exp[?(1735 ± 55)/T], and k (n?C8H18) = (4.31 ± 0.39) × 1011 exp[?(1415 ± 65)T] cm3 mol?1 s?1 for the temperature range studied. For the butane and hexane reactions, we have also applied the CRDS technique to extend our temperature range down to 297 K; the results obtained by the decay of C6H5 with CRDS agree fully with those determined by absolute product yield measurements with PLP/MS. Weighted least‐squares analyses of these two sets of data gave rise to k (n?C4H10) = (2.70 ± 0.15) × 1011 exp[?(1880 ± 127)/T] and k (n?C6H14) = (4.81 ± 0.30) × 1011 exp[?(1780 ± 133)/T] cm3 mol?1 s?1 for the temperature range 297‐‐1046 K. From the absolute rate constants for the two larger molecular reactions (C6H5 + n‐C6H14 and n‐C8H18), we derived the rate constant for H‐abstraction from a secondary C? H bond, ks?CH = (4.19 ± 0.24) × 1010 exp[?(1770 ± 48)/T] cm3 mol?1 s?1. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 49–56, 2004 相似文献
944.
P. Budrugeac J. M. Criado F. J. Gotor J. Malek L. A. Prez‐Maqueda E. Segal 《国际化学动力学杂志》2004,36(6):309-315
The isoconversional method suggested by Friedman and the invariant kinetic parameters method (IKP) were used in order to examine the kinetics of the nonisothermal crystallization of (GeS2)0.3(Sb2S3)0.7. The objective of the paper is to show the usefulness of the IKP method both for determining the activation parameters as well as the model of the investigated process. It was shown that the kinetic triplet [(E, A, f(α), where E is the activation energy, A is the preexponential factor, and f(α) is the differential function of conversion], which results through the application of the IKP method, depends on the set of kinetic models considered. For different sets of kinetic models, proportional values of f(α) are obtained. A criterion for the selection of this set, the use of which lead to the true kinetic triplet corresponding to the analyzed process (E = 163.2 kJ mol?1; A = 2.47 × 1012 min?1 and the Avrami‐Erofeev model, Am, for m = 2.5–2.6 was suggested. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 309–315, 2004 相似文献
945.
Jean Dolbeault Maria J Esteban Michael Loss Luis Vega 《Journal of Functional Analysis》2004,216(1):1-21
We prove some sharp Hardy-type inequalities related to the Dirac operator by elementary, direct methods. Some of these inequalities have been obtained previously using spectral information about the Dirac-Coulomb operator. Our results are stated under optimal conditions on the asymptotics of the potentials near zero and near infinity. 相似文献
946.
Alick KT Law Deepak Gupta Shawn Levy Douglas C Wallace Robert J McKeon Charles R Buck 《BMC neuroscience》2004,5(1):1
Background
The adenine nucleotide translocator 1 (Ant1) is an inner mitochondrial membrane protein involved with energy mobilization during oxidative phosphorylation. We recently showed that rodent Ant1 is upregulated by transforming growth factor-beta (TGF-β) in reactive astrocytes following CNS injury. In the present study, we describe the molecular mechanisms by which TGF-β1 regulates Ant1 gene expression in cultured primary rodent astrocytes. 相似文献947.
The European Physical Journal C - The tracking system of the LHCb detector has been re-optimised to reduce the amount of material which particles traverse. The different subcomponents involved in... 相似文献
948.
We study the minimal and maximal closed extension of a differential operator A on a manifold B with conical singularities, when A acts as an unbounded operator on weighted L
p
-spaces over B, 1<p<∞. Under suitable ellipticity assumptions we can define a family of complex powers A
z
, zℂ. We also obtain sufficient information on the resolvent of A to show the boundedness of the purely imaginary powers. Examples concern unique solvability and maximal regularity for the
solution of the Cauchy problem for the Laplacian on conical manifolds as well as certain quasilinear diffusion equations.
Received: 12 June 2001; in final form: 3 June 2002 /
Published online: 1 April 2003
Mathematics Subject Classification (2000): 35J70, 47A10, 35K57 相似文献
949.
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
950.
Measures of complexity for 3D image analysis of trabecular
bone 总被引:1,自引:0,他引:1
Based on fractal properties and spatial auto-correlation, the
measures of complexity lacunarity, Moran's I and Geary's C index
are defined for 3D image analysis. Their abilities to investigate
translational invariance, characteristic length scales, spatial
correlation and shapes of 3D micro-structures are demonstrated on
proto-typical examples. Finally, using these measures of complexity,
3D images of trabecular bone are analysed. The main findings are
that the complexity of the trabecular structure decreases and the
plate-like shapes of the trabeculae change to mainly rod-like shapes
during bone loss. These results and the proposed measures could have
a great impact for medicine and for space exploration. 相似文献