全文获取类型
收费全文 | 91649篇 |
免费 | 853篇 |
国内免费 | 183篇 |
专业分类
化学 | 49189篇 |
晶体学 | 1364篇 |
力学 | 3773篇 |
综合类 | 1篇 |
数学 | 9815篇 |
物理学 | 28543篇 |
出版年
2022年 | 657篇 |
2021年 | 982篇 |
2020年 | 1131篇 |
2019年 | 1213篇 |
2018年 | 1715篇 |
2017年 | 1776篇 |
2016年 | 2339篇 |
2015年 | 1235篇 |
2014年 | 1963篇 |
2013年 | 3787篇 |
2012年 | 3459篇 |
2011年 | 3992篇 |
2010年 | 3034篇 |
2009年 | 2985篇 |
2008年 | 3592篇 |
2007年 | 3531篇 |
2006年 | 3426篇 |
2005年 | 3113篇 |
2004年 | 2786篇 |
2003年 | 2514篇 |
2002年 | 2542篇 |
2001年 | 2627篇 |
2000年 | 1993篇 |
1999年 | 1468篇 |
1998年 | 1315篇 |
1997年 | 1224篇 |
1996年 | 1136篇 |
1995年 | 1057篇 |
1994年 | 1020篇 |
1993年 | 1061篇 |
1992年 | 1092篇 |
1991年 | 1140篇 |
1990年 | 1045篇 |
1989年 | 1074篇 |
1988年 | 1018篇 |
1987年 | 949篇 |
1986年 | 881篇 |
1985年 | 1052篇 |
1984年 | 1143篇 |
1983年 | 952篇 |
1982年 | 1001篇 |
1981年 | 891篇 |
1980年 | 852篇 |
1979年 | 917篇 |
1978年 | 1044篇 |
1977年 | 1032篇 |
1976年 | 942篇 |
1975年 | 872篇 |
1974年 | 904篇 |
1973年 | 856篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
991.
O. S. Filipenko L. L. Alimova L. O. Atovmyan B. M. Bolotin 《Russian Chemical Bulletin》1989,38(8):1631-1634
A planar structure for molecules of 2-(2-methylaminophenyl)-4H-3,1-benzoxazine-4-one was found by x-ray structural analysis. Shortening of the N-Ph bond and lengthening of the distance between amino- and azine-N atoms in comparison to the tosyl analog was demonstrated to lead to a bathochromic shift of the absorption spectrum and a hypsochromic displacement of the luminescence spectrum. As a result, the Stokes shift of 2-(2-methylaminophenyl)-4H-3,1-benzoxazine-4-one is smaller than that of 2-(2-tosylaminophenyl)-4H-3,1-benzoxazine-4-one. In the crystal, molecules of 2-(2-methylaminophenyl)-4H-3,1-benzoxazine-4-one are stacked with intermolecular interaction energy between molecules in the stack of –12.5 and –14.2 kcal/mole. The stacks are joined into layers parallel to (010).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1781–1785, August, 1989. 相似文献
992.
B. S. Fedorov M. A. Fadeev V. V. Arakcheeva G. V. Strukov N. I. Golovina R. F. Trofimova G. V. Shilov L. O. Atovmyan 《Russian Chemical Bulletin》1994,43(12):2087-2090
A novel heterocyclic compound, 4-acetoxy-5,6-dihydro-5,5-dinitro-2H-1,3-oxazineN-oxide, has been synthesized by the reaction of the dipotassium salt of 1,1,5,5-tetranitro-3-oxapentane with aqueous acetic acid. The synthesized compound has been studied by X-ray diffraction analysis.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2207–2210, December, 1994.We would like to thank G. V. Lagodzinskaya (Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences) for recording and interpreting1H NMR spectra, A. M. Korolev (Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences) for helpful discussion, and V. I. Fetisov (Institute of Physiologically Active Compounds, Russian Academy of Sciences) for performing quantum-chemical calculations by the AM1 SCF MO LCAO method. 相似文献
993.
Some novel physical ideas and mathematical techniques are described, useful in the development of effective Hamiltonian methods for studying molecular environmental effects. 相似文献
994.
A. A. Korlyukov K. A. Lyssenko M. Yu. Antipin A. G. Shipov O. A. Zamyshlyaeva E. P. Kramarova Vad. V. Negrebetsky S. A. Pogozhikh Yu. E. Ovchinnikov Yu. I. Baukov 《Russian Chemical Bulletin》2004,53(9):1924-1931
The reaction of 4-(2-hydroxybenzoyl)-2,2,6,6-tetramethyl-2,6-disilamorpholine with BF3Et2O afforded (O-B)-chelate 4-[2-(difluoroboroxy)benzoyl]-2,2,6,6-tetramethyl-2,6-disilamorpholine. Treatment of the latter with BF3Et2O or SOCl2 gave rise to products of the disilamorpholine ring opening, viz., (O-B) chelate 2-(difluoroboroxy)-N,N-bis(dimethylfluorosilylmethyl)benzamide or 2-(difluoroboroxy)-N, N-bis(dimethylchlorosilylmethyl)benzamide, respectively. The structures of the compounds synthesized were confirmed by X-ray diffraction analysis and 1H, 13C, and 29Si NMR spectroscopy. High-precision X-ray diffraction study and quantum-chemical calculations demonstrated that the coordination OSi bond is absent in the two last-mentioned compounds.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1846–1853, September, 2004. 相似文献
995.
The reaction of carboxymethyl polysaccharides and their ethyl esters with amines was studied with the aim to determine how the structure of the polymeric acylating agent affects the composition of the reaction products. 相似文献
996.
997.
V. D. Orlov N. V. Getmanskii O. V. Shishkin E. E. Lakin V. P. Kuznetsov 《Chemistry of Heterocyclic Compounds》1993,29(3):301-306
By the reaction of 2-nitrochalcone with hydrazine hydrate, 5-(2-nitrophenyl)-3-phenyl-1H-2-pyrazoline (I) and the hydrazone of 3-(5-(2-nitrophenyl)-3-phenyl-2-pyrazolin-1-yl)-3-(2-nitrophenyl)propiophenol (II) have been prepared. The acylation of both compounds I and II leads to N-acyl derivatives of the first. The acylating ability of formamide and N,N-dimethylformamide was observed in reactions with pyrazoline I. An x-ray structural study was carried out on compound II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 360–366, March, 1993. 相似文献
998.
I. V. Moiseeva P. M. Lukin O. E. Nasakin V. N. Romanov V. A. Tafeenko A. Kh. Bulai P. A. Sharbatyan 《Chemistry of Heterocyclic Compounds》1992,28(2):237-237
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, p. 282, February, 1992. 相似文献
999.
1000.
F. M. Stoyanovich E. P. Zakharov O. V. Lysenko V. N. Yarovenko M. M. Krayushkin 《Russian Chemical Bulletin》1991,40(1):225-227
Preparative syntheses have been developed for 2-amino-5-cyano-1,3,4-oxadiazole from the semicarbazone of methyl glyoxylate and some of its transformations were studied. This product is an important intermediate in the preparation of its derivatives.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1. 243–246, January, 1991. 相似文献