全文获取类型
收费全文 | 221004篇 |
免费 | 2980篇 |
国内免费 | 1320篇 |
专业分类
化学 | 122945篇 |
晶体学 | 3229篇 |
力学 | 8892篇 |
综合类 | 61篇 |
数学 | 24423篇 |
物理学 | 65754篇 |
出版年
2020年 | 1757篇 |
2019年 | 1897篇 |
2018年 | 2486篇 |
2017年 | 2534篇 |
2016年 | 3654篇 |
2015年 | 2426篇 |
2014年 | 3541篇 |
2013年 | 8888篇 |
2012年 | 7698篇 |
2011年 | 9420篇 |
2010年 | 6658篇 |
2009年 | 6458篇 |
2008年 | 8803篇 |
2007年 | 8910篇 |
2006年 | 8394篇 |
2005年 | 7720篇 |
2004年 | 6880篇 |
2003年 | 6066篇 |
2002年 | 6002篇 |
2001年 | 6709篇 |
2000年 | 5077篇 |
1999年 | 3675篇 |
1998年 | 3039篇 |
1997年 | 3017篇 |
1996年 | 3017篇 |
1995年 | 2626篇 |
1994年 | 2725篇 |
1993年 | 2588篇 |
1992年 | 2837篇 |
1991年 | 2903篇 |
1990年 | 2705篇 |
1989年 | 2623篇 |
1988年 | 2559篇 |
1987年 | 2501篇 |
1986年 | 2521篇 |
1985年 | 3305篇 |
1984年 | 3363篇 |
1983年 | 2811篇 |
1982年 | 3054篇 |
1981年 | 2816篇 |
1980年 | 2614篇 |
1979年 | 2795篇 |
1978年 | 3000篇 |
1977年 | 3039篇 |
1976年 | 3063篇 |
1975年 | 2801篇 |
1974年 | 2913篇 |
1973年 | 2956篇 |
1972年 | 2319篇 |
1971年 | 1846篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
L. D. Smirnov S. V. Nikitin A. I. Chernyshev A. A. Sorokin V. P. Lezina V. G. Zabrodnyaya M. M. Kaganskii 《Chemistry of Heterocyclic Compounds》1992,28(12):1425-1431
It has been shown that the alkylation of 2-methyl-9-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-one takes place at the oxygen atom, but electrophilic substitution takes place mainly at position 8 of the molecule (the ortho position relative to the hydroxy group).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1660–1666, December, 1992. 相似文献
993.
Fe2+/Fe3+ ratio versus sediment depth values have been determined for ten lakes in British Columbia. The values often reflect the local topography of the lakes, the weathering history of the deposited minerals, and the diagenesis of the minerals after deposition in the lake. 相似文献
994.
L Jirovetz G Buchbauer W J?ger A Woidich A Nikiforov 《Biomedical chromatography : BMC》1992,6(3):133-134
After inhalation experiments with sandalwood oil and the pure fragrance compounds coumarin and alpha-terpineol, substances were detected and measured in the blood samples of test animals (mice) using gas chromatography/mass spectrometry (GC/MS) (MID) in connection with GC/FTIR (SWC), GC/AES (carbon and oxygen trace) and flame ionization detection/gas chromatography. Using tiglinic acid benzyl ester as the internal standard the following concentrations in serum could be found: alpha-santalol 6.1 ng/mL, beta-santalol 5.3 ng/mL and alpha-santalene 0.5 ng/mL. In separate inhalation experiments with coumarin and with alpha-terpineol the corresponding concentrations were 7.7 ng/mL and 6.9 ng/mL, respectively. 相似文献
995.
996.
Ultrasonic wave propagation in cancellous and cortical bone: prediction of some experimental results by Biot's theory. 总被引:1,自引:0,他引:1
J L Williams 《The Journal of the Acoustical Society of America》1992,91(2):1106-1112
Pulse transmission ultrasound was used to determine the longitudinal wave speed along the direction of trabecular alignment in 32 water-saturated anisotropic tibial bovine cancellous bone samples and in one cortical bone sample also from the bovine tibia. These results are compared to published ultrasound wave-speed data obtained from bovine femoral specimens. Nonlinear regression was used to fit Biot's theory to the data. The correlation coefficient for regression analysis between the experimental ultrasound velocities and the velocities predicted by Biot's theory was r = 0.78. 相似文献
997.
998.
Dumbgen L. 《Journal of multivariate analysis》1995,52(2)
A particular class of tests for the principal components of a scatter matrix Σ is proposed. In the simplest case one wants to test whether a given vector is an eigenvector of Σ corresponding to its largest eigenvalue. The test statistics are likelihood ratio statistics for the classical Wishart model, and critical values are obtained parametrically as well as nonparametrically without making any assumptions on the eigenvalues of Σ. Still, the tests have asymptotic properties similar to those of classical procedures and are asymptotically admissible and optimal in some sense. 相似文献
999.
S. A. Chernyak O. V. Shekhter N. L. Sergovskaya Yu. S. Tsizin 《Chemistry of Heterocyclic Compounds》1992,28(7):832-834
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 994–996, July, 1992. 相似文献
1000.
Recently Svanberg et al. [Optics Lett. 11 (1986) 138; J. Opt. Soc. Am. B 4 (1987) 462] obtained saturated absorption resonances with subnatural linewidth by working in the regime of high pumping intensities and optically thick atomic samples. We analyze here this new spectroscopic regime, within the formalism of Maxwell-Bloch-type equations, in the case of a Doppler broadened medium having two nearly degenerate but uncoupled resonances. We show that even in this most favourable case it is not possible to resolve spectral features that lie within the natural linewidth. 相似文献