全文获取类型
收费全文 | 413篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
化学 | 257篇 |
晶体学 | 5篇 |
力学 | 11篇 |
数学 | 79篇 |
物理学 | 76篇 |
出版年
2023年 | 1篇 |
2022年 | 23篇 |
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 21篇 |
2013年 | 12篇 |
2012年 | 26篇 |
2011年 | 26篇 |
2010年 | 25篇 |
2009年 | 15篇 |
2008年 | 17篇 |
2007年 | 24篇 |
2006年 | 25篇 |
2005年 | 17篇 |
2004年 | 9篇 |
2003年 | 16篇 |
2002年 | 17篇 |
2001年 | 11篇 |
2000年 | 16篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有428条查询结果,搜索用时 31 毫秒
321.
Ibrahim Abdul Razak Anwar Usman Hoong‐Kun Fun Bohari M. Yamin Goh Wooi Keat 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):m31-m33
In the title compound, [Zn(CH3COO)2(C4H8N2S)2]·H2O, the Zn atom is tetrahedrally coordinated in the ZnO2S2 form. N—H?O and O—H?O intramolecular and intermolecular hydrogen bonds are formed by the four N atoms and the water molecule. N—H?O intermolecular hydrogen bonds and C—H?S and C—H?O intermolecular interactions interconnect columns formed by the molecules into layers. Adjacent layers are then linked by other N—H?O and O—H?O intermolecular hydrogen bonds to form a three‐dimensional framework throughout the structure. The orientations of the acetate planes are such that the Zn atom lies within them. 相似文献
322.
From DTA curves, energy (E), enthalpy (Ha), entropy (Sa) and free-energy (G
a) of activation and the pre-exponential factor (k
0) for diffusion-controlled crystal growth of calcium tungstate from solutions in sodium tungstate melts were estimated using the Arrhenius equationk
Dl=k
0
e
–E/RT.E increased linearly with increased cooling rate (R
T). The change ofk
0 was parallel to that ofk
Dl and increased with increasingR
T but there was no direct correlation.H
a,S
a andG
a were unaffected by the changes of RT and crystallization temperature (T
0). The distance (d
12), between a diffusing particle and its host crystal necessary for a successful diffusion, was estimated. Such distances increased with increasingT
0 andR
T.
Zusammenfassung Aus DTA-Kurven wurden Energie (E), Enthalpie (H a), Entropie (S a) und freie Energie (G a) der Aktivierung, sowie der prä-exponentielle Faktor (k 0) für das diffusionsbedingte Kristallwachstum von Calciumwolframat aus Natriumwolframatschmelzen unter Anwendung einer gewöhnlichen Arrheniusgleichungk D=k 0 e –E/RT abgeschätzt. Mit zunehmenden Abkühlgeschwindigkeiten (RT) nimmtE linear zu.k 0 verhält sich parallel zuk D und nimmt mit steigendemR T zu, jedoch ohne direkte Korrelation.H a,S a undG a verhielten sich unabhängig von Änderungen vonR T und der Kristallisationstemperatur (T 0). Die zur erfolgreichen Diffusion erforderliche Entfernung (d 12) zwischen einem diffundierenden Teilchen und seinem Empfängerkristall wurde geschätzt. Diese Abstände nahmen mit steigendemT 0 undR T zu.
Résumé On a estimé, à partir de courbes ATD, l'énergie (E), l'enthalpie (H a), l'entropie (S a) et l'enthalpie libre (G a) de l'activation ainsi que le facteur pré-exponentiel (k 0) de la croissance des cristaux, contrôlée par la diffusion, du tungstate de calcium, dans des solutions de tungstate de sodium fondu, à l'aide d'une équation d'Arrhenius ordinaire:k D=k 0 e –E/RT.E augmente linéairement avec les vitesses croissantes de refroidissement (R T),k 0 est parallèle àk D et augmente quandR T croît; cependant il n'y a pas de corrélation directe.H a,S a etH a restent indépendants des variations d'R T et de la température de cristallisation (T 0). On a estimé la distance (d 12) nécessaire, entre une particule en diffusion et son cristal-hôte, pour une diffusion réussie. Ces distances augmentent avec les valeurs croissantes deT 0 etR T.
k l,=k 0 e –E/RT, (E), (H a), (S a), (G a) (k 0) - . (E) (R T). (K 0) k l, R T, . H a,S a,G a R T, (T 0). (d 12) «», . 0 R T.相似文献
323.
Akagi K Guo S Mori T Goh M Piao G Kyotani M 《Journal of the American Chemical Society》2005,127(42):14647-14654
A series of crown ether type binaphthyl derivatives (CEBDs) were synthesized and used as chiral dopants to induce chiral nematic (N*) liquid crystals (LCs). The twisting powers of the CEBDs for phenylcyclohexane (PCH)-derived nematic LCs were evaluated. It was found that the twisting powers of the CEBDs increased with decreasing ring size of the crown ether. Helical polyacetylenes were synthesized in the N*-LCs induced by the CEBDs. The relationship between the morphology of the helical polyacetylene and the helical structure of the N*-LC was investigated. The result showed that the interdistance between the fibril bundles of the helical polyacetylene was equal to a half-helical pitch of the N*-LC and the screw direction of the polyacetylene fibrils was opposite to that of the N*-LC. 相似文献
324.
The interactions of the benzothiazolate complex, CpCr(CO)(2)(SCSN(C(6)H(4))) (2), and the tetrazole thiolate complex, CpCr(CO)(3)(eta(1)-SCN(4)Ph) (3), with controlled amounts of Me(3)OBF(4) and (MeO)(2)SO(2), respectively, produced the corresponding mu(3)-oxo trinuclear thionate-bridged complexes, [Cp(3)Cr(3)(mu(2)-OH)(mu(3)-O)(mu(2)-eta(2)-SCSN(C(6)H(4)))(2)](5)BF(4) (45%) and [Cp(3)Cr(3)(mu(2)-OH)(mu(3)-O)(mu(2)-eta(2)-SCN(4)Ph)(2)](9)(MeOSO(3)) (53%), together with their respective free dimethylated thiolate ligands, [MeSCSNMe(C(6)H(4))](4)BF(4) and (Me(2)SCN(4)Ph)(8)MeOSO(3). The reaction of 3 with Me(3)OBF(4) resulted in the isolation of a binuclear complex, [Cp(2)Cr(2)(mu-OH)(mu-eta(2)-SCN(4)Ph)(2)](7)BF(4) (43%), and (8)BF(4) (27%). The reaction of the thiopyridine complex, CpCr(CO)(2)(SPy) (4), with I(2) also produced a similar mu(3)-oxo complex 10 (31%), together with CpCrI(2)(THF) (11) and the disulfide (SPy)(2). Similar reactions with 2 and 3 and I(2) yielded species 5 and 7, together with 11 and disulfides derived from their respective ligands. Cyclic voltammograms recorded in solutions of 5 and 9 indicated that the compounds could be reduced and oxidized at very similar potentials. An EPR spectrum characteristic of a compound with axial symmetry was obtained for 9 at 7 K. Single-crystal X-ray diffraction analyses confirmed that species 7 is dinuclear, whereas 5 and 9 are structural trinuclear analogues, each containing a mu(3)-oxo central core. 相似文献
325.
High‐quality DFT calculations are employed to estimate the arene exchange energies for reactions of general formula: For C60 and C70 complexes of Cr(CO)3, full geometry optimizations at the DFT level using moderately large basis sets were performed, while for the other systems a hybrid approach was developed in which the geometries were obtained at the PM3(tm) level and the energetics were evaluated at the DFT level. C70 is shown to be a slightly better arene ligand than C60; however, no enhancements of arene‐like bonding capabilities are seen for C78 and C84 relative to C70. Explicit calculation of a series of exchange energies at the DFT level using both DFT and PM3(tm) geometries demonstrates that PM3(tm) geometries are sufficiently accurate for the calculation of energetics at a higher theoretical level, but PM3(tm) calculations are inadequate for a quantitative assessment of exchange energies. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1881–1886, 2001 相似文献
326.
Summary The applicability of a recently developed micro-attachment adaptable to common atomic-absorption spectrometers has been extended to include both cold-vapour atomic-absorption and gas-phase ultraviolet-absorption measurements. The cold-vapour atomic-absorption technique for the determination of total mercury in human whole blood and hair samples was applied by homogenizing the samples in a strongly alkaline medium and using stannous chloride-cadmium chloride mixture as reducing agent. Application of the system to the determination of volatile molecular species in aqueous solution by gas-phase ultraviolet-absorption spectrophotometry have also been studied, with NH3 as a model. This technique provides a simple, sensitive, yet selective method for the determination of ammoniacal and total nitrogen in aqueous samples and gives results comparable to those obtained by the standard distillation-titration method.
Presented at the 8th International Microchemical Symposium, Graz, Austria, 1980. 相似文献
Zusammenfassung Die Anwendbarkeit eines kürzlich entwickelten Gerätes für die gewöhnliche Atomabsorptionsspektrometrie wurde erweitert sowohl für die Messung der Kaltdampf-Atomabsorption wie für die Messung der UV-Absorption in der Gasphase. Erstere wurde zur Bestimmung des Gesamtquecksilbers in menschlichem Gesamtblut und in Haarproben nach deren Homogenisierung in stark alkalischem Medium und Verwendung einer Mischung von SnCl2 und CdCl2 als Reduktionsmittel herangezogen. Auch die Anwendung des Gerätes für die Bestimmung flüchtiger Stoffe in wäßriger Lösung durch UV-Absorptions-Spektrophotometrie wurde geprüft, wobei Ammoniak als Modellsubstanz diente. Dieses einfache, empfindliche und selektive Verfahren eignet sich zur Bestimmung von ammoniakalischem und von Gesamtstickstoff in wäßrigen Proben. Die Ergebnisse sind mit denen der Standard-Destillation-Titration vergleichbar.
Presented at the 8th International Microchemical Symposium, Graz, Austria, 1980. 相似文献
327.
Supramolecular side chain liquid crystalline polymers were prepared from poly(3-carboxypropylmethylsiloxane) (PSI100) and azobenzene-based derivatives through intermolecular hydrogen bonding between the carboxylic acid groups of PSI100 and the imidazole rings in the azobenzene-based derivatives. The presence of H-bonding was confirmed using FTIR spectroscopy. The polymeric complexes behave as liquid crystalline polymers and exhibit nematic mesophases identified on the basis of the observation of Schlieren textures. The mesogenic behaviour of these complexes was studied by polarizing optical microscopy and X-ray diffraction. The thermal behaviour of the complexes was investigated by differential scanning calorimetry. On increasing the spacer length, the transition temperatures initially increase. A further increase in spacer length, however, leads to a decrease in the transition temperatures. The electron donor-acceptor interaction between unlike mesogenic units in supramolecular copolymeric complexes helps to stabilize the mesophase. 相似文献
328.
329.
Rui Min Vivian Goh Kim Huey Ee Aileen Pua Yunle Huang Shao Quan Liu Benjamin Lassabliere Bin Yu 《Journal of mass spectrometry : JMS》2022,57(2):e4810
In this study, neutral loss scan and high-resolution MS/MS were used in combination to detect and tentatively identify various flavonoid and limonoid glycosides in navel orange albedo, juice, peel and pulp. These compound classes are of research interest due to their flavour and bioactive properties, and although flavonoid glycosides have been previously studied in other food matrices, to the best of our knowledge, neutral loss scans have not been used for the elucidation of limonoid glycosides. Neutral loss masses of 120, 162 and 308 Da were selected for the detection of hexose, rutinose and neohesperidose-substituted flavonoids, whereas 197 Da was explored for limonoid glycosides due to their tendency to form ammonium adducts. Fragmentation patterns obtained from targeted MS/MS were then used to differentiate rutinose and neohesperidose substituents as well as flavonoid subclasses of flavones, flavanones and flavonols. Additionally, high-resolution MS/MS was also used for the identification of aglycones by accurate mass (to four decimal places), allowing for the differentiation of aglycones with similar unit masses but different chemical formulas. In total, 19 flavonoid glycosides and six limonoid glycosides were detected. This workflow allows for a rapid screening of flavonoid and limonoid glycosides in citrus, which can be further extended to other food products such as tea. 相似文献
330.
Liu YH Huang SX Zhao QS Ding JK Goh NK Sun HD Chia TF Tan SN Chia LS 《Natural product research》2008,22(10):860-864
A new ent-kaurane diterpenoid, lophanthodin G (1) and one known abietanoid, 6alpha-hydroxyferruginol (2), were isolated from the leaves of Isodon lophanthoides var. geradianus. The structure of the new compound 1 was established using spectroscopic methods including extensive 1D and 2D NMR analysis. 相似文献