全文获取类型
收费全文 | 286篇 |
免费 | 10篇 |
专业分类
化学 | 260篇 |
数学 | 10篇 |
物理学 | 26篇 |
出版年
2024年 | 1篇 |
2022年 | 8篇 |
2021年 | 16篇 |
2020年 | 6篇 |
2019年 | 10篇 |
2018年 | 15篇 |
2017年 | 6篇 |
2016年 | 16篇 |
2015年 | 10篇 |
2014年 | 7篇 |
2013年 | 22篇 |
2012年 | 17篇 |
2011年 | 16篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 16篇 |
2007年 | 13篇 |
2006年 | 11篇 |
2005年 | 19篇 |
2004年 | 11篇 |
2003年 | 8篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
排序方式: 共有296条查询结果,搜索用时 867 毫秒
81.
Victoria A. Ivolgina Margarita S. Chernov’yants Leonid D. Popov Vitaliy V. Suslonov Natalya A. Avtushenko Nikolay V. Luanguzov 《Phosphorus, sulfur, and silicon and the related elements》2020,195(5):421-428
AbstractAs a part of investigation of thyreostatic activity of mercapto-substituted triazoles, the structure, spectroscopic properties of 4-amino-5-(furan-2-yl)-4H-1,2,4-triazole-3-thione were obtained. 4-amino-5-(furan-2-yl)-4H-1,2,4-triazole-3-thione forms steady charge-transfer complex in dilute chloroform solution, coordinating one iodine molecule (lgβ?=?3.47). The reaction product of 4-amino-5-(furan-2-yl)-4H-1,2,4-triazole-3-thione is presented by uncharged adduct: C6H6N4OS·I2. The crystal structure of the adduct was studied in detail by single crystal X-ray diffraction. The results of thermogravimetric analysis revealed the stability of adduct in a solid state at the temperature range 50–500?°C. 相似文献
82.
The development of a microfluidic biosensor module with fluorescence detection for the identification of pathogenic organisms and viruses is presented in this article. The microfluidic biosensor consists of a network of microchannels fabricated in polydimethylsiloxane (PDMS) substrate. The microchannels are sealed with a glass substrate and packed in a Plexiglas housing to provide connection to the macro-world and ensure leakage-free flow operation. Reversible sealing permits easy disassembly for cleaning and replacing the microfluidic channels. The fluidic flow is generated by an applied positive pressure gradient, and the module can be operated under continuous solution flow of up to 80 microL min(-1). The biosensor recognition principle is based on DNA/RNA hybridization and liposome signal amplification. Superparamagnetic beads are incorporated into the system as a mobile solid support and are an essential part of the analysis scheme. In this study, the design, fabrication and the optimization of concentrations and amounts of the different biosensor components are carried out. The total time required for an assay is only 15 min including sample incubation time. The biosensor module is designed so that it can be easily integrated with a micro total analysis system, which will combine sample preparation and detection steps onto a single chip. 相似文献
83.
The synthesis of 7-chloro-, 7-bromo-, and 7-iodo-substituted 7-deaza-2′-deoxyguanosine derivatives 2b – d is described. The regioselective 7-halogenation with N-halogenosuccinimides was accomplished using 7-[2-deoxy-3,5-O-di(2-methylpropanoyl)-β-D -erythro- pentofuranosyl]-2-(formylamino)-4-methoxy-7H-pyrrolo[2,3-d]- pyrimidine ( 4 ) as the common precursor. A one-pot reaction (2N aq. NaOH) of the halogenated intermediates 5a – c furnished the desired compounds. Also the 7-hexynyl derivative 2e of 7-deaza-2′-deoxyguanosine is described. 相似文献
84.
Kolomeitsev AA Bissky G Barten J Kalinovich N Lork E Röschenthaler GV 《Inorganic chemistry》2002,41(23):6118-6124
Hexaalkylguanidinium and 2-(dialkylamino)-1,3-dimethylimidazolinium trimethyldifluorosiliconates, precursors for two stable hexaalkylguanidinium perfluoroalkoxides, were synthesized by treating commercially available bis(dialkylamino)difluoromethane derivatives with (dialkylamino)trimethylsilanes in aprotic media. With hexamethylguanidinium pentafluoroethoxide the introduction of the lipophilic and electronegative C2F5O group was straightforwardly achieved in the case of primary and secondary alkyl triflates to furnish the respective fluorinated ethers. The molecular structures of [(CH2NMe)2C(NEt2)]+[Me3SiF2]- and [C(NMe2)3]+F-*6CH2Cl2 were determined, showing in the latter case a fluoride anion octahedrally coordinated by six methylene chloride molecules via hydrogen bridges with a F...H distance of 205 pm (C...F distance 270.0(3) pm). 相似文献
85.
2-Aryl-6-cyano-7-methyl-5-indolizinones were successfully converted into 2-aryl-5-chloro-6-cyano-7-methylindolizines. The obtained 5-chloroindolizines readily underwent nucleophilic substitution at position 5 leading in high yields to novel 5-functionalised indolizines. 相似文献
86.
A solution-phase synthesis for the preparation of substituted 2-(1,2,4-triazol-3-yl)benzimidazoles from triazole aldehydes and ortho-phenylenediamines has been developed for the purpose of producing diverse lead generation libraries. Crude products were obtained and further purified by mass-guided preparative HPLC. 相似文献
87.
Dieter Naumann Natalya V. Kirij Nicola Maggiarosa Wieland Tyrra Yurii L. Yagupolskii Mathias S. Wickleder 《无机化学与普通化学杂志》2004,630(5):746-751
Syntheses and Characterizations of the First Tris and Tetrakis(trifluoromethyl) Palladates(II) and Platinates(II), [M(CF3)3(PPh3)]— and [M(CF3)4]2— (M = Pd, Pt) Tris(trifluoromethyl)(triphenylphosphino)palladate(II) and platinate(II), [M(CF3)3PPh3]—, and the tetrakis(trifluoromethyl)metallates, [M(CF3)4]2— (M = Pd, Pt), are prepared from the reactions of [MCl2(PPh3)2] and Me3SiCF3 / [Me4N]F or [I(CF3)2]— salts in good yields. [Me4N][M(CF3)3(PPh3)] crystallize isotypically in the orthorhombic space group Pnma (no. 62) with Z = 4. The NMR spectra of the new compounds are described. 相似文献
88.
Natalya Ramzaeva Helmut Rosemeyer Peter Leonard Klaus Mühlegger Frank Bergmann Herbert vonderEltz Frank Seela 《Helvetica chimica acta》2000,83(6):1108-1126
The 2′‐deoxypseudouridine ( 5 ) was functionalized at N(1) with methyl acrylate by Michael addition. The resulting methyl 2′‐deoxypseudouridine‐1‐propanoate ( 6 ) was converted to the phosphoramidite 8 and to the amino‐functionalized derivative 9 , which was transformed into the fluorescein‐labeled phosphoramidites 14 and 16 . Fluorescent oligonucleotides were synthesized either from these building blocks or by post‐synthetic modification of oligomers containing 2′‐deoxypseudouridine subunits. The stability of oligonucleotide duplexes was determined from the melting profiles, measured by UV‐ or VIS‐light absorbance, as well as from the fluorescence emission spectra. While small spacer residues did not affect the thermal stability of the 2′‐deoxypseudouridine‐containing duplexes, large dye residues led to destabilization. 相似文献
89.
The synthesis of the 7-deaza-2′-deoxyinosine derivatives 3a – c with chloro, bromo, and iodo substituents at position 7 is described. Glycosylation of the 7-halogenated 6-chloro-7-deazapurines 4a – c or of the 7-halogenated 6-chloro-7-deaza-2-(methylthio)purines 9a – c with 2-deoxy-3,5-di-O-(4-toluoyl)-α-D -erythro-pentofuranosyl chloride ( 5 ) furnished the intermediates 7a – c and 11a – c , respectively, which gave, upon deprotection, the desired nucleosides 3a – c . 相似文献
90.
Irene L. Odinets Natalya M. Vinogradova Konstantin A. Lyssenko Michail Yu. Antipin Pavel V. Petrovskii Tatyana A. Mastryukova 《Heteroatom Chemistry》2002,13(1):1-21
Intramolecular S‐alkylation in a series of ω‐haloalkyl‐substituted thiophosphorylacetonitriles 5–7 presents an effective synthetic route to the hitherto unknown 3‐cyano‐2‐oxo‐1,2‐thiaphospholanes 14 and thiaphosphinanes 15 . The compounds were obtained as a mixture of cis‐ and trans‐isomers that were resolved to individual stereoisomers in most cases. For some of them, X‐ray diffraction analysis has been performed. It was shown that 31P NMR spectroscopy can be used to assign the stereochemistry of 3‐cyano‐2‐oxo‐1,2‐thiaphosphacyclanes. © 2002 John Wiley & Sons, Inc. Heteroatom Chem 13:1–21, 2002; DOI 10.1002/hc.1101 相似文献