全文获取类型
收费全文 | 563篇 |
免费 | 42篇 |
国内免费 | 5篇 |
专业分类
化学 | 507篇 |
力学 | 2篇 |
数学 | 75篇 |
物理学 | 26篇 |
出版年
2023年 | 7篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 21篇 |
2019年 | 17篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 24篇 |
2015年 | 27篇 |
2014年 | 36篇 |
2013年 | 37篇 |
2012年 | 62篇 |
2011年 | 71篇 |
2010年 | 47篇 |
2009年 | 25篇 |
2008年 | 37篇 |
2007年 | 30篇 |
2006年 | 20篇 |
2005年 | 17篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 5篇 |
1979年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 3篇 |
1966年 | 4篇 |
1965年 | 2篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1957年 | 2篇 |
1919年 | 1篇 |
排序方式: 共有610条查询结果,搜索用时 46 毫秒
1.
Zusammenfassung Die Eigenschaften anomerer n-Amyl- und n-Hexyl-ketoside der N-Acetyl-d-neuraminsäure und ihrer kristallisierenden Tetra-O-acetyl-derivate wurden miteinander verglichen. Den durch Neuraminidase nicht spaltbaren Glykosiden, die durch Erhitzen von N-Acetyl-d-neuraminsäure mit chlorwasserstoff-haltigem Amyl- bzw. Hexylalkohol erhalten werden konnten und eine stärkere Linksdrehung zeigen, wird die -Konfiguration, den früher1 nach dem Verfahren vonKoenigs undKnorr über die Pentaacetyl-2-chlorneuraminsäure dargestellten und durch Neuraminidase spaltbaren Anomeren die -Konfiguration zugeschrieben.
Mit 2 Abbildungen 相似文献
A comparison has been made of the properties of the anomeric n-amyl and n-hexyl ketosides of N-acetyl-d-neuraminic acid and of their crystalline peracetyl derivatives. The more levorotatory anomers, which have been prepared by heating N-acetyl-d-neuraminic acid with amyl or hexyl alcohol containing dry hydrogen chloride and which are not attacked by neuraminidase, are assigned the -configuration, whereas the -configuration is attributed to the anomers which have previously1 been obtained via pentaacetyl-2-chloro-neuraminic acid by the method ofKoenigs andKnorr and have proved to be cleaved by neuraminidase.
Mit 2 Abbildungen 相似文献
2.
The impact of spilled explosives, their by-products and degradation products on human beings and the environment has been
recognised as a serious problem at areas of existing and former ammunition plants. In nature, aerobic and anaerobic degradation
processes of explosives and their accompanying compounds yield polar contaminants with relatively high water solubilities.
Most are potentially carcinogenic and mutagenic. An HPLC method applying UV-detection for nitroaromatic compounds and amperometric
detection for aminoaromatic and phenolic compounds was used for monitoring the degradation of explosives in a polluted groundwater
sample under natural conditions. Analysis was performed by direct injection of aliquots of the sample after exposition to
daylight for different periods of time.
Received: 6 January 1996/Revised: 7 March 1996/Accepted: 13 March 1996 相似文献
3.
Heinrich Hahn Kurt Utvary Wolfgang Meindl 《Monatshefte für Chemie / Chemical Monthly》1983,114(11):1167-1175
Reaction of (CH3NHPF4)2 with selected organometallic reagents yields (CH3NPF3)2, while reaction with non-nucleophilic bases such as 1,4-diazabicyclo[2.2.2]octane (DABCO) or 1,8-Bis(dimethylamino)naphthalin and with alkali fluorides yields ionic compounds with the diazoniadiphosphatetidine ring as a dianion. 相似文献
4.
Stefan Müllegger Kathrin H?nel Thomas Strunskus Christof W?ll Adolf Winkler 《Chemphyschem》2006,7(12):2552-2558
Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has been applied to reveal the molecular arrangement of ultrathin oligophenyl films [p-quaterphenyl (4P) and p-hexaphenyl (6P)] on Au(111). In the half-monolayer films the molecules lie flat on the surface but still have a considerable inter-ring twist of 30 degrees -40 degrees , similar to the gas-phase conformation. In the saturated monolayer film the second half of the molecules is side-tilted by an angle of less than 66 degrees with respect to the surface. This arrangement is already similar to that in bulk net planes of thicker films parallel to the surface, that is, the 4P(211) and 6P(21-3) planes, respectively. 相似文献
5.
Threshold energies Et are determined for photoelectron emission by 20 inorganic anions in aqueous solution (7.1 < Et < 9.1 eV). Calculated values of Et for Cl?, Br?, I? agree with experiment. The Et are correlated with charge-transf absorption spectra. 相似文献
6.
The impact of spilled explosives, their by-products and degradation products on human beings and the environment has been
recognised as a serious problem at areas of existing and former ammunition plants. In nature, aerobic and anaerobic degradation
processes of explosives and their accompanying compounds yield polar contaminants with relatively high water solubilities.
Most are potentially carcinogenic and mutagenic. An HPLC method applying UV-detection for nitroaromatic compounds and amperometric
detection for aminoaromatic and phenolic compounds was used for monitoring the degradation of explosives in a polluted groundwater
sample under natural conditions. Analysis was performed by direct injection of aliquots of the sample after exposition to
daylight for different periods of time.
Presented as a poster at the Anakon ’95 Conference in Schliersee, April 24–26, 1995 相似文献
7.
Kathrin Wichmann Bianca Antonioli Tilo Shnel Marco Wenzel Kerstin Gloe Karsten Gloe Jason R. Price Leonard F. Lindoy Alexander J. Blake Martin Schrder 《Coordination chemistry reviews》2006,250(23-24):2987
In the discussion that follows some of the more recent progress in the area of anion binding by synthetic polyamine receptors is presented, with emphasis given to work undertaken by the authors’ groups. A continuing theme in these studies has been the relationship between receptor structure and its anion extraction properties.Systematic solvent extraction and structural studies for halide and perrhenate complexes with polyamines of tripodal, macrocyclic and macrobicyclic architecture that contain both aromatic moieties and four to eight amine functions have been performed in order to derive relevant structure-binding/extractability relationships. The results demonstrate that the binding and extraction behaviour of the polyamines towards halides and perrhenate is a complex function of their structural features, degree of protonation and lipophilic properties. The extraction is characterized by the preferred formation of mono- and diprotonated amine species in the organic phase. X-ray structure studies of iodide and perrhenate complexes with open-chain tetraamino derivatives and octaamino cryptands in different protonation states lead to the conclusion that in the first case only limited chelation of the anion occurs and in the second only highly protonated species are able to encapsulate the anion. The structural patterns observed are strongly influenced by the presence of water molecules in the crystals. 相似文献
8.
J. Meindl I. V. Arkhangelskii N. A. Chernova 《Journal of Thermal Analysis and Calorimetry》1981,20(1):39-46
A method is suggested for the affine transformation of thermoanalytical curves, by means of which their comparison with one another becomes feasible. It is demonstrated that the results obtained by the traditional methods of non-isothermal kinetics depend on the heating rate, whereas the results attained by affine transformation are independent of the heating rate. They are consistent with the results obtained by Merzhanov's dmethod, which is also a non-aprioristic method.
Zusammenfassung Eine Methode zur Affintransformierung thermoanalytischer Kurven wird vorgeschlagen, wodurch ihr Vergleich miteinandere rmöglicht wird. Es wird gezeigt, daß die durch traditionelle Methoden der nicht-isothermen Kinetik erhaltenen Ergebnisse von der Aufheizgeschwindigkeit abhängig sind, während die durch Affintransformierung erhaltenen von der Aufheizgeschwindigkeit unabhängig sind. Sie sind in Übereinstimmung mit den nach der Methode von Merzhanov erhaltenen Ergebnissen, die ebenfalls eine nicht-aprioristische Methode ist.
Résumé On propose une méthode pour la transformation affine des courbes d'analyse thermique, qui permet leur comparaison. On montre que les résultats obtenus par les méthodes traditionnelles de cinétique non-isotherme dépendent de la vitesse du chauffage, tandis que les résultats obtenus par la transformation affine n'en dépendent pas. Ils sont en accord avec les résultats de la méthode de Merzhanov.
, . , , , , , , . , , .相似文献
9.
Jimmy Maillard Kathrin Klehs Christopher Rumble Eric Vauthey Mike Heilemann Alexandre Fürstenberg 《Chemical science》2021,12(4):1352
Although biological imaging is mostly performed in aqueous media, it is hardly ever considered that water acts as a classic fluorescence quencher for organic fluorophores. By investigating the fluorescence properties of 42 common organic fluorophores recommended for biological labelling, we demonstrate that H2O reduces their fluorescence quantum yield and lifetime by up to threefold and uncover the underlying fluorescence quenching mechanism. We show that the quenching efficiency is significantly larger for red-emitting probes and follows an energy gap law. The fluorescence quenching finds its origin in high-energy vibrations of the solvent (OH groups), as methanol and other linear alcohols are also found to quench the emission, whereas it is restored in deuterated solvents. Our observations are consistent with a mechanism by which the electronic excitation of the fluorophore is resonantly transferred to overtones and combination transitions of high-frequency vibrational stretching modes of the solvent through space and not through hydrogen bonds. Insight into this solvent-assisted quenching mechanism opens the door to the rational design of brighter fluorescent probes by offering a justification for protecting organic fluorophores from the solvent via encapsulation.Overtones and combinations of O–H vibrations in the solvent efficiently quench red-emitting fluorophores by resonant energy transfer. 相似文献
10.
It was found that the first step of thermal decomposition of the pyridinium salt of 1,3-bis(trimethylsilyl)-2, 4-dimercapto-2,4-dithioxo-1,3-diaza-25,45-diphosphetidine (I) most probably involves breakdown to the acid form HS(S)P(NHSiMe3)2P(S)SH (II). The latter is very unstable and decomposes further, the end-product being a polymer (PNS)x. In this work, the mechanism of this process is investigated.
Zusammenfassung Man fand, daß der erste Schritt der thermischen Zersetzung des Pyridiniumsalzes von 1,3-Bis(trimethylsilyl)-2,4-dimercapto-2,4-dithioxo-1,3-diaza-25,45-diphosphetidin (I) sehr wahrscheinlich einen Abbau zur Säureform HS(S)P(NHSiMe3)2P(S)SH (II) beinhaltet. Letztere ist sehr unbeständig und zersetzt sich, wobei als Endprodukt ein (PNS)x-Polymer entsteht. In vorliegendem Manuskript wird der Mechanismus dieses Prozesses näher untersucht.相似文献