全文获取类型
收费全文 | 2276篇 |
免费 | 189篇 |
国内免费 | 93篇 |
专业分类
化学 | 2498篇 |
晶体学 | 3篇 |
综合类 | 2篇 |
物理学 | 55篇 |
出版年
2024年 | 2篇 |
2023年 | 27篇 |
2022年 | 30篇 |
2021年 | 40篇 |
2020年 | 81篇 |
2019年 | 47篇 |
2018年 | 62篇 |
2017年 | 59篇 |
2016年 | 76篇 |
2015年 | 63篇 |
2014年 | 102篇 |
2013年 | 222篇 |
2012年 | 126篇 |
2011年 | 164篇 |
2010年 | 119篇 |
2009年 | 151篇 |
2008年 | 139篇 |
2007年 | 138篇 |
2006年 | 139篇 |
2005年 | 128篇 |
2004年 | 120篇 |
2003年 | 104篇 |
2002年 | 135篇 |
2001年 | 39篇 |
2000年 | 30篇 |
1999年 | 17篇 |
1998年 | 27篇 |
1997年 | 18篇 |
1996年 | 27篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 1篇 |
1988年 | 7篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 9篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1971年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有2558条查询结果,搜索用时 15 毫秒
1.
Martin Kellert Jan-Simon Jeshua Friedrichs Nadine Anke Ullrich Alexander Feinhals Jonas Tepper Peter Lnnecke Evamarie Hey-Hawkins 《Molecules (Basel, Switzerland)》2021,26(7)
The development of novel, tumor-selective and boron-rich compounds as potential agents for use in boron neutron capture therapy (BNCT) represents a very important field in cancer treatment by radiation therapy. Here, we report the design and synthesis of two promising compounds that combine meta-carborane, a water-soluble monosaccharide and a linking unit, namely glycine or ethylenediamine, for facile coupling with various tumor-selective biomolecules bearing a free amino or carboxylic acid group. In this work, coupling experiments with two selected biomolecules, a coumarin derivative and folic acid, were included. The task of every component in this approach was carefully chosen: the carborane moiety supplies ten boron atoms, which is a tenfold increase in boron content compared to the l-boronophenylalanine (l-BPA) presently used in BNCT; the sugar moiety compensates for the hydrophobic character of the carborane; the linking unit, depending on the chosen biomolecule, acts as the connection between the tumor-selective component and the boron-rich moiety; and the respective tumor-selective biomolecule provides the necessary selectivity. This approach makes it possible to develop a modular and feasible strategy for the synthesis of readily obtainable boron-rich agents with optimized properties for potential applications in BNCT. 相似文献
2.
This minireview describes the strategies for synthesis of fiuorinated surfactants potentially nonbioaccumulable.Various strategies have been focused on(Ⅰ) reducing the length of the perfluorocarbon chain,(Ⅱ) introducing hetero atoms into the fluorocarbon chain,(Ⅲ) introducing branch(herein and after branch means the fluoro-carbon chain section is not straight).In most cases,the surface tensions versus the surfactant concentrations have been assessed.These above strategies led to various highly fiuorinated(perfluorinated or not perfluorinated) surfactants whose chemical changes enabled to obtain novel alternatives to perfluorooctanoic acid(PFOA) and perfluorooctane sulphonate(PFOS). 相似文献
3.
4.
In this paper we highlighted the synthesis, characterization, and practical exploitation of different types of polyphosphazenes substituted with fluorinated groups. There are several ways in which fluorine atoms can be inserted into polyphosphazenes, all of which leading to different polymers showing a wide range of characteristics. In general it is true that the insertion of fluorine atoms into phosphazene macromolecules leads to an enhancement of the thermal stability, flame resistance, low-temperature elastomericity, and chemical inertness of the phosphazenes obtained. The contribution of Italian research groups to the preparation and exploitation of organic commercial macromolecules grafted onto fluorinated polyphosphazenes is also reviewed. 相似文献
5.
The reaction of a new fluorinated unsymmetrical allenylazine with dimethyl acetylenedicarboxylate and phenylacetylene affords the combined intra-intermolecular criss-cross cycloaddition products, 2,3-disubstituted-1,10-diazatricyclo[5.2.1.04,10]deca-2,6-diene derivatives. The products contain three fused five-membered rings with two nitrogen atoms within an unsaturated heterocyclic system. The structures were assigned using 2D NMR correlations and in the case of the phenylacetylene adduct by X-ray structure analysis. 相似文献
6.
Terminal alkynes undergo mild and efficient aminomethylation with aqueous formaldehyde and secondary amines under CuI catalysis. In most cases high to nearly quantitative yields of tertiary propargylamines are obtained in DMSO solution at room temperature. Aromatic, aliphatic and silylated acetylenes as well as alkynols can be used. Primary amines are less reactive and satisfactory yields of secondary propargylamines are obtained only with phenylacetylene. 相似文献
7.
V. I. Saloutin I. T. Bazyl' Z. E. Skryabina P. N. Kondrat'ev O. N. Chupakhin 《Russian Chemical Bulletin》1994,43(2):279-282
Reactions of pentafluorobenzoylpyruvic acid with amines afford the respective enamines. The intramolecular cyclization of the latter results inN-substituted 4-quinolone-2-carboxylic acids. Ammonia and triethylamine favor the cyclization of pentafluorobenzoylpyruvic acid to 2-carboxychromone.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 299–302, February, 1994. 相似文献
8.
Maria Carmelita Kasuya 《Journal of fluorine chemistry》2007,128(5):562-565
A series of fluorinated galactosides, dodecyl 2-deoxy-2-fluoro-β-d-galactopyranoside (2F Gal), dodecyl 4-deoxy-4-fluoro-β-d-galactopyranoside (4F Gal) and dodecyl 6-deoxy-6-fluoro-β-d-galactopyranoside (6F Gal), was chemically synthesized and introduced to B16 cells to serve as scaffolds for cellular enzyme glycosylation. Results showed that the presence of fluorine exercised significant effects on cell viability. Among the fluorinated galactosides used, 2F Gal was glycosylated to afford a GM4 analogue. 相似文献
9.
J.S. Yadav B.V. Subba Reddy V. Sunitha K. Srinivasa Reddy K.V.S. Ramakrishna 《Tetrahedron letters》2004,45(42):7947-7950
Aryl amines react with endocyclic ene-carbamates such as tert-butyl 2,3-dihydro-1H-1-pyrrolecarboxylate and tert-butyl 1,2,3,4-tetrahydro-1-pyridinecarboxylate, on the surface of montmorillonite KSF clay under mild conditions to afford the corresponding 3-aminopropylhexahydropyrrolo[3,2-c]quinoline or 4-aminobutyloctahydrobenzo[h][1,6]naphthyridine derivatives in excellent yields with moderate diastereoselectivity. 相似文献
10.
The use of reagent concentration has resulted in increased rates for all stages of the REM resin synthesis of tertiary amines. These increases in rate translate into faster reaction times, higher yields and lower reagent consumption. Of the methods examined, the most successful was the use of perfluorous solvents, either alone or with a small amount of organic co-solvent. 相似文献