首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   465篇
  免费   3篇
  国内免费   3篇
化学   316篇
晶体学   7篇
力学   12篇
数学   27篇
物理学   109篇
  2021年   5篇
  2020年   17篇
  2019年   17篇
  2018年   18篇
  2017年   14篇
  2016年   26篇
  2015年   4篇
  2014年   16篇
  2013年   17篇
  2012年   16篇
  2011年   14篇
  2010年   10篇
  2009年   15篇
  2008年   19篇
  2007年   20篇
  2006年   15篇
  2005年   14篇
  2004年   11篇
  2003年   21篇
  2002年   25篇
  2001年   14篇
  2000年   5篇
  1999年   8篇
  1995年   4篇
  1994年   3篇
  1993年   5篇
  1992年   3篇
  1991年   3篇
  1990年   6篇
  1989年   6篇
  1987年   5篇
  1986年   6篇
  1985年   9篇
  1984年   5篇
  1983年   4篇
  1982年   3篇
  1981年   3篇
  1980年   3篇
  1979年   3篇
  1978年   4篇
  1977年   4篇
  1976年   4篇
  1975年   3篇
  1974年   2篇
  1973年   7篇
  1972年   4篇
  1971年   3篇
  1970年   2篇
  1969年   4篇
  1967年   10篇
排序方式: 共有471条查询结果,搜索用时 15 毫秒
81.
2-Amino-5-aryl(pyridyl)-6H-1,3,4-thiadiazines ana isomeric 2-hydrazino-4-aryl(pyridyl)thiazoles, the ratio of which depends on the reaction conditions, were obtained by the reaction of substituted phenacyl bromides and bromoacetylpyridines with thiosemicarbazide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 843–846, June, 1991.  相似文献   
82.
Coupling of 3-alkyl-4-aryl-1H-pyrazole-5-diazonium chlorides with methylene-active methyl phenacyl sulfones afforded new pyrazolo[5,1-c][1,2,4]triazine derivatives via cyclization of the corresponding intermediate 1-aryl-2-(hetarylhydrazinylidene)-2-(methanesulfonyl)ethanones. The reactivity of the methanesulfonyl group on C3 of pyrazolo[5,1-c][1,2,4]triazines toward some nucleophiles was studied.  相似文献   
83.
A reaction of triphenylbismuth with 2,4,6-tribromophenol and hydrogen peroxide (molar ratio 1 : 2 : 1) in ether affords triphenylbismuth bis(2,4,6-tribromophenoxide). The complex obtained was structurally characterized by X-ray diffraction analysis. The coordination polyhedron of the Bi atom is a trigonal bipyramid with axial aroxy groups. The Bi–C and Bi–O bond lengths are 2.202(4), 2.203(4), 2.212(4) and 2.241(3), 2.245(3) Å, respectively. The intramolecular Bi···Br(1,4) contacts are 3.629(1) and 4.077(1) Å, respectively.  相似文献   
84.
A number of new organic luminophores was synthesized by PO olefination from 2- (4-bromomethylphenyl)-5-phenyloxazole and -1,3,4-oxadiazole and various heterocyclic aldehydes that contain a furan ring. The absorption and fluorescence spectra of the products in toluene, as well as their scintillation characteristics, were measured. The effect of the electronic nature of the substituents on the spectral-luminescence properties of the luminophores is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 617–621, May, 1982.  相似文献   
85.
The crystal structure of 2-[(4-nitrophenyl)carbonyl]cyclohex-1-ene-1-yl 4-nitrobenzoate is studied (T = 173 K, R1 = 0.0354 for 2713 observed reflections). This crystal is orthorhombic, a = 7.8367(8) Å, b = 9.6082(10) Å, c = 23.856(3) Å, V = 1796.3(3) Å3, space group P212121, and Z = 4. The molecule has a folded configuration, which is stabilized by π-π interactions between its two parts. A system of intermolecular C-H...O hydrogen bonds (H...O, 2.44–2.67 Å; CHO angles 122°–169°) and intramolecular C-H...O contacts closing five-membered cycles (H...O, 2.42–2.59 Å; CHO angles 96°–102°) are formed in the structure.  相似文献   
86.
Optics and Spectroscopy - The features and possibilities of absorption molecular spectroscopy of complex mixtures of organic compounds have been studied by the example of fractions of thermal...  相似文献   
87.
Crystallography Reports - The reactions of interaction of N,N'-di(4-chlorophenyl)diimide 1,1'-binaphtyl-4,4',5,5',8,8'-hexa-carboxylic acid (cubogen red) with thiourea dioxide...  相似文献   
88.
In this Essay, we present a critical analysis of two common practices in modern chemistry—that is, of using speculations about the “greenness” and “nontoxicity” of developed synthesis procedures and of a priori labelling various compounds derived from natural sources as being environmentally safe. We note that every organic molecule that contains functional groups should be biologically active. Thus, analysis of the particular greenness and the potential environmental impact of a given chemical process should account for the biological activity of all its components in a measureable (rather than empirical) way. We highlight the necessity of clarifying discussions on biological activity and toxicity and propose possible ways of introducing tox-Profiles as a reliable overview of the overall toxicity of chemical reactions.  相似文献   
89.
Doklady Physics - Electron back-scattering diffraction shows that a package structure consisting of colonies of tetragonal lamella plates is formed when cooled below the temperature of the...  相似文献   
90.
Temperature dependences of dielectric constant, amplitude of the third harmonic and heat capacity for the organic ferroelectric of diisopropylammonium iodide (C6H16NI) have been investigated. The measurements were carried out through heating and cooling cycles in the range of 300–400?K. It was found that upon the first heating, only one phase transition occurred without the presence of the ferroelectric phase. For samples preheated over 420?K, two phase transitions at 363 and 378?K appeared in the heating process, and the ferroelectric state was also observed between them. Upon cooling, the ferroelectric phase was detected in the range of lower 361?K and persisted up to room temperature.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号