全文获取类型
收费全文 | 688133篇 |
免费 | 27745篇 |
国内免费 | 18435篇 |
专业分类
化学 | 340416篇 |
晶体学 | 10091篇 |
力学 | 39469篇 |
综合类 | 36篇 |
数学 | 99147篇 |
物理学 | 245154篇 |
出版年
2021年 | 6360篇 |
2020年 | 6955篇 |
2019年 | 8515篇 |
2018年 | 11483篇 |
2017年 | 12386篇 |
2016年 | 15992篇 |
2015年 | 9750篇 |
2014年 | 15157篇 |
2013年 | 32006篇 |
2012年 | 25851篇 |
2011年 | 30906篇 |
2010年 | 25731篇 |
2009年 | 26462篇 |
2008年 | 27413篇 |
2007年 | 26480篇 |
2006年 | 24435篇 |
2005年 | 21880篇 |
2004年 | 21674篇 |
2003年 | 19247篇 |
2002年 | 19278篇 |
2001年 | 20944篇 |
2000年 | 16047篇 |
1999年 | 13049篇 |
1998年 | 11333篇 |
1997年 | 10835篇 |
1996年 | 10409篇 |
1995年 | 9679篇 |
1994年 | 9822篇 |
1993年 | 9720篇 |
1992年 | 9695篇 |
1991年 | 9983篇 |
1990年 | 9384篇 |
1989年 | 9333篇 |
1988年 | 8813篇 |
1987年 | 8411篇 |
1986年 | 8042篇 |
1985年 | 9501篇 |
1984年 | 9864篇 |
1983年 | 8030篇 |
1982年 | 8574篇 |
1981年 | 8082篇 |
1980年 | 7719篇 |
1979年 | 8220篇 |
1978年 | 8494篇 |
1977年 | 8587篇 |
1976年 | 8845篇 |
1975年 | 7910篇 |
1974年 | 7779篇 |
1973年 | 8077篇 |
1972年 | 6355篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
A simple method is proposed for increasing the accuracy of computation of the eigenvalues of elliptic operators, which does not require high-order accurate schemes.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 63, pp. 63–68, 1987. 相似文献
43.
Yoshiaki Murata Cheng-Huang Lin Totaro Imasaka 《Fresenius' Journal of Analytical Chemistry》1993,346(6-9):543-544
Summary A supersonic jet spectrum of 9,10-dichloroanthracene is measured by stimulated-emission-pumping fluorescence dip spectrometry and conventional fluorescence spectrometry. The performance obtained is compared for these spectrometric methods, providing same information concerned with the energy level of the ground state. The former is more preferential for measurement of a high-resolution spectrum, since the spectral resolution is determined by the linewidth of the dumping laser. On the other hand, the latter is more preferential for measurement with better sensitivity at the expense of the spectral resolution, since the fluorescence throughput can be improved by increasing the slit width of the monochromator.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
44.
I. M. Karnaukh A. S. Moskovkin G. V. Ponomarev 《Chemistry of Heterocyclic Compounds》1994,30(1):20-25
The mass spectral behavior of 1, 2-di (mesoetioporphyr inyl-1)- and 1, 2-di (mesooctaethylporphyrlnyl) ethanes and ethylenes, their Cu and Ni complexes, as well as Ni Schiff bases of 1, 2-di (mesooctaethylporphyrinyl)ethane complexes, under ionization by electron impact and bombardment by accelerated atoms, was studied. Peaks of molecular ions, for which the basic decomposition pathways were established on the basis of an analysis of the parent and daughter ions, were observed in the electron impact mass spectra of all these compounds.For Communication 29, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 24–29, January, 1994. 相似文献
45.
V. A. Samsonov L. B. Volodarskii V. L. Korolev G. Kh. Khisamutdinov 《Chemistry of Heterocyclic Compounds》1994,30(10):1243-1249
The reaction of 4-aminobenzofurazan with aryldiazonium salts leads to the formation of 4-amino-5-aryl-azobenzofurazans and 5-amino-2-aryl-4-nitroso-2H-benzotriazoles, products of the rearrangement of the initially formed 4-amino-7-(arylazo)benzofurazans. Oxidation of the benzofurazan as well as of the triazole derivatives gives 7-aryl-1,2,3-triazol[4,5-e]benzofurazans. The chemical properties of some of the compounds obtained have been investigated.Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1432–1438, October, 1994. Original article submitted July 25, 1994. 相似文献
46.
Molecular n-v complexes of quinoline N-oxides with BF3 have been studied by electronic and IR spectroscopy. In most case the donor centre is the oxygen atom of the N-oxide group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1087–1092, August, 1994. 相似文献
47.
S. V. Litvinenko V. I. Savich L. D. Bobrovnik 《Chemistry of Heterocyclic Compounds》1994,30(3):340-344
We have developed a method for synthesis of N-(3-clzloro-2-quinoxalyl)sulfonamides by reaction of 2,3-dichloroquinoxaline with substituted arylsufonamides. Based on the IR spectra, we have established that in the solid state, the synthesized compounds exist in the form of amide tautomers. Alkylation of these compounds leads to N-metliyl-N-(3-chloro-2-quinoxalyl)arylsulfonamides. We demonstrate the possibility of nucleophilic substitution of the halogen upon treatment with O- and N-nucleophiles. The use of bifunctional nucleophiles leads to condensed quinoxalines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 30, No. 3, pp. 387–392, March, 1994. 相似文献
48.
49.
M. A. Mikhaleva B. M. Bolotin T. A. Kizner E. S. Serebrykova 《Chemistry of Heterocyclic Compounds》1994,30(1):79-81
We have synthesized 5-alkyl(alkoxy)-2-(o-lzydroxy-p-alkoxyphenyl)pyrimidines and considered the effect of the OH group on the inesomorphism. We have found that in binuclear o-hydroxyarylpyrimidines, an ortho OH group forming an intramolecular hydrogen bond increases Tmp, inhibits the appearance of nematic properties, and promotes the appearance of a smectic A.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 30, No. 1, pp. 90–92, January, 1994. 相似文献
50.
A. Sh. Isamukhamedov N. P. Goncharova A. I. Glushetskova 《Chemistry of Natural Compounds》1994,30(2):170-174
The influence of sunflowerseed and cottonseed oils and also of fractions of normal and oxidized triacylglycerols isolated from them on cytochrome P-450 from rat liver microsomes has been investigated. 相似文献