全文获取类型
收费全文 | 407709篇 |
免费 | 3450篇 |
国内免费 | 951篇 |
专业分类
化学 | 189739篇 |
晶体学 | 6450篇 |
力学 | 21390篇 |
综合类 | 7篇 |
数学 | 59852篇 |
物理学 | 134672篇 |
出版年
2021年 | 3127篇 |
2020年 | 3330篇 |
2019年 | 3762篇 |
2018年 | 11918篇 |
2017年 | 12618篇 |
2016年 | 10500篇 |
2015年 | 4817篇 |
2014年 | 7122篇 |
2013年 | 16002篇 |
2012年 | 15761篇 |
2011年 | 24768篇 |
2010年 | 16808篇 |
2009年 | 16793篇 |
2008年 | 21813篇 |
2007年 | 24596篇 |
2006年 | 12305篇 |
2005年 | 15893篇 |
2004年 | 12517篇 |
2003年 | 11452篇 |
2002年 | 9859篇 |
2001年 | 10519篇 |
2000年 | 7932篇 |
1999年 | 5998篇 |
1998年 | 5002篇 |
1997年 | 4823篇 |
1996年 | 4645篇 |
1995年 | 3958篇 |
1994年 | 3904篇 |
1993年 | 3777篇 |
1992年 | 4160篇 |
1991年 | 4375篇 |
1990年 | 4167篇 |
1989年 | 4083篇 |
1988年 | 3862篇 |
1987年 | 3994篇 |
1986年 | 3756篇 |
1985年 | 4713篇 |
1984年 | 4777篇 |
1983年 | 3975篇 |
1982年 | 4055篇 |
1981年 | 3781篇 |
1980年 | 3735篇 |
1979年 | 4015篇 |
1978年 | 4016篇 |
1977年 | 3931篇 |
1976年 | 3940篇 |
1975年 | 3722篇 |
1974年 | 3663篇 |
1973年 | 3723篇 |
1972年 | 2638篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
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
212.
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
213.
214.
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
215.
Kh. T. Mirzaazimova S. D. Gusakova A. I. Glushenkova 《Chemistry of Natural Compounds》1994,30(5):555-558
The yields and fatty acid compositions of the free lipids and lipids weakly and strongly bound to proteins from seeds of cottonplant varieties resistant and susceptible to verticillium wilt have been determined and the changes in these indices in the seeds of the infected plants have been measured. It has been established that the seeds of healthy plants of the two varieties are similar in the qualitative compositions of the lipids and fatty acids but differ with respect the amounts of lipids in them bound with protein in different ways and with respect to the amounts of the individual fatty acids. The observed changes in the lipid and fatty-acid compositions depend on the degree of resistance of the variety to wilt. 相似文献
216.
217.
A. Aitmambetov S. N. Shinkaruk S. P. Bondarenko V. P. Khilya 《Chemistry of Natural Compounds》1994,30(4):453-456
6-Halogeno-1,3-benzodioxane analogs of chalcones have been synthesized by various methods. Flavanone and flavone analogs of silandrin and hydnocarpin have been obtained from them. The structures of the new flavonoids have been shown by their PMR spectra. 相似文献
218.
Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 891475.
Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 679–680, September–October, 1994. 相似文献
219.
S. A. Mamedova 《Chemistry of Natural Compounds》1994,30(2):267-268
Institute of Botany, Academy of Sciences of the Republic of Azerbaidzhan, Baku. Translated from Khimiya Prirodnykh Soedinenii,
No. 2, pp. 291–292, March–April, 1994. 相似文献
220.