全文获取类型
收费全文 | 349篇 |
免费 | 4篇 |
专业分类
化学 | 264篇 |
晶体学 | 3篇 |
力学 | 3篇 |
数学 | 35篇 |
物理学 | 48篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 11篇 |
2014年 | 21篇 |
2013年 | 24篇 |
2012年 | 24篇 |
2011年 | 20篇 |
2010年 | 17篇 |
2009年 | 19篇 |
2008年 | 23篇 |
2007年 | 27篇 |
2006年 | 17篇 |
2005年 | 23篇 |
2004年 | 15篇 |
2003年 | 15篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1979年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1965年 | 2篇 |
1939年 | 1篇 |
1938年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有353条查询结果,搜索用时 15 毫秒
1.
Angla Schwartz Lszl Szab Katalin Pusztay-Szab Istvn Hermecz Zoltn Mszros 《Journal of heterocyclic chemistry》1987,24(3):655-660
Ultraviolet-visible spectra of 4-oxo 1 and 4-imino 2 quinolizines or their monocyclic tautomers 3, 4 have been studied in neutral, acidic and basic ethanolic solution as well as in dimethyl sulfoxide and chloroform. Ring B of 4-oxo and 6-unsubstituted 4-imino compounds can be cleaved by sodium ethanolate more or less easily. Ring B of 6-methyl-4-iminoquinolizines is very unstable and they are present mainly in the monocyclic form which are partly dissociated in ethanol and dimethyl sulfoxide especially in higher dilution or in the presence of sodium ethanolate. In dilute acidic ethanol or chloroform, the dissociation is suppressed and in the latter solvent and in some cases, absorption bands can be observed due to a small amount of the 4-imino-6-methylquinolizines. In acidic solution of compounds 3B=C, 3D, 4E, 4F=G having simultaneously cyano and ethoxycarbonyl groups in 1 and 3 position, not simple reprotonation occurs but irreversible changes can be observed. 相似文献
2.
The aim of the paper is to investigate the limit behaviour of the least squares estimator of the shift parameter of nearly unstable, nearly stable, and nearly explosive AR(1) models. Both zero start and stationary cases are treated. Connection with the maximum likelihood estimator of the shift parameter of continuous time AR(1) processes is also discussed. 相似文献
3.
Katalin E. Kövér Dušan Uhr?&#x;n Victor J. Hruby 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):162-168
A pulsed field gradient version of the sensitivity-enhanced 2D TOCSY experiment is proposed which yields high-quality spectra with improved sensitivity and a minimum of two scans pert1increment. For rapid acquisition of 1D TOCSY spectra, the 1D DPFGSE–TOCSY experiment was modified to include phase-encoded multiple-selective excitation followed by a simple spectral editing. Combination of these two building blocks is used in a sensitivity-enhanced 2D analog of the 3D TOCSY–TOCSY experiment which provides an efficient tool for resolving severely overlapped signals of oligomers in short experimental time. 相似文献
4.
The reaction between thiocarbamate herbicides and 2,6-dichlorobenzoquinone-N-chloroimine or 2,6-dibromobenzoquinone-N-chloroimine is suitable for the detection of these herbicides on thin-layer plates with high sensitivity. The reactions were followed by infrared, nuclear magnetic resonance and mass spectrometry. We have established the formation of 2,6-dichlorobenzoquinone-S-alkyl sulphenylimines. In the case of the bromo-derivative, halogen exchange and substitution on the quinone ring took place simultaneously leading to the formation of mixed halogenated 2,6-dihalo- and, in addition, 2,3,6-trihalobenzoquinone-S-alkyl sulphenylimines. The final product of the detection reaction, i.e. 2,6-dichlorobenzoquinone-S-alkyl sulphenylimine was reacted with 2,6-dibromobenzoquinone-N-chloroimine where 2,6-dichloro-3-bromobenzoquinone-S-alkyl sulphenylimine formed as a consequence of the looser bromine-carbon linkage on the 2 and 6 positions of the quinone ring. 相似文献
5.
Valentina Domenici Carlo Alberto Veracini Katalin Fodor-Csorba Giacomo Prampolini Ivo Cacelli Andrjia Lebar Bostjan Zalar 《Chemphyschem》2007,8(16):2321-2330
The orientational properties of the banana-shaped liquid crystal 4-chloro-1,3-phenylenebis{4-[4'-(10-undecenyloxy)]benzoyloxy} benzoate (ClPbis11BB) are reported in the nematic phase under the effect of an external magnetic field. A new hypothesis, which states that the central ring of the aromatic core is oriented perpendicularly to the external magnetic field, is proposed. In support of this hypothesis, a series of studies based on (2)H NMR spectroscopy, both in the bulk and in solution, are discussed. (2)H NMR measurements on three selectively deuterium-labelled isotopomers are presented, together with DFT results from B3LYP/cc-pvDz calculations performed on the aromatic core. The rather flat shape of the investigated intramolecular energy surface allows for several different conformations to be populated, the computed magnetic susceptibilities of which are consistent with the proposed hypothesis of peculiar orientation of banana-shaped molecules. Moreover, the orientation of the magnetic susceptibility tensor is shown to be strongly dependent on the internal conformation of the banana-shaped molecules. 相似文献
6.
Medzihradszky KF Leffler H Baldwin MA Burlingame AL 《Journal of the American Society for Mass Spectrometry》2001,12(2):215-221
A biologically active protein fraction was isolated from rabbit intestine, purified by one-dimensional SDS-PAGE and stained with Coomassie Brilliant Blue. A predominant band of approximately 110-130 kDa was excised and digested in-gel with trypsin. The resulting peptides were extracted then separated by microbore reversed-phase high-performance liquid chromatography (HPLC). Mass spectrometric data from one HPLC fraction obtained by two different ionization techniques proved to be complementary. Matrix-assisted laser desorption/ionization (MALDI) showed nine peptide masses, which by post source decay analysis and database searching were attributed to two proteins. Nanoflow electrospray analysis performed on a hybrid tandem mass spectrometer of quadrupole-quadrupole-orthogonal acceleration time-of-flight (QqTOF) geometry detected six additional peptide components. On the basis of the additional peptides and superior quality collision-induced dissociation spectra typical of this instrument type, two further proteins were identified. The resolution afforded by the QqTOF instrument permitted charge state determination for the fragment ions while preserving the high detection sensitivity that was essential in obtaining the composition of this mixture of proteins. 相似文献
7.
Dusanka Ž. Obadović Anikó Vajda Maya Garić A. Bubnov Vera Hamplová M. Kašpar Katalin Fodor-Csorba 《Journal of Thermal Analysis and Calorimetry》2005,80(2):519-523
Summary Thermal properties of a homologous series of ferroelectric liquid crystals S-(-)-[4-(2-n-alkoxy-propionyloxy)]biphenyl-4'-[n-alkoxy-(3,5-dimethyl)]benzoate have been investigated by polarizing optical microscopy and differential scanning calorimetry.
The mesophases were identified and confirmed by X-ray too. Three binary mixtures were prepared from the individual homologues.
In one of the mixtures (Mix1), the ferroelectric SmC* phase has broadened and became enantiotropic. This mesophase remained
monotropic in the other two mixtures (Mix2, Mix3). The chiral nematic N* phase did not appear in Mix1, but remained monotropic
for the other two mixtures. Two molecular parameters, the layer spacing and the average intermolecular distance have been
calculated from the X-ray results for the homologues and their mixtures. An intercalated tail-to-tail packing of molecules
was found both in the single compounds and their mixtures resulting in the layer spacing about half of the molecular length
of the single compounds. 相似文献
8.
Tamás?Kovács Tamás?Turányi Katalin?F?gleinEmail author János?Szépv?lgyi 《Plasma Chemistry and Plasma Processing》2005,25(2):109-119
Decomposition of carbon tetrachloride in a RF thermal
plasma reactor was investigated in argon atmosphere. The net
conversion of CCl4 and the main products of its decomposition
were determined from the mass spectrometric analysis of outlet
gases. Flow and temperature profiles in the reactor were
calculated and concentration profiles of the species along the
axis of the reactor were estimated using a newly developed
chemical kinetic mechanism, containing 12 species and 34 reaction
steps. The simulations indicated that all carbon tetrachloride
decomposed within a few microseconds. However, CCl4 was partly
recombined from its decomposition products. The calculations
predicted 70\% net conversion of CCl4, which was close to the
experimentally determined value of 60\%. A thermodynamic
equilibrium model also simulated the decomposition. Results of the
kinetic and thermodynamic simulations agreed well above 2000 K.
However, below 2000 K the thermodynamic equilibrium model gave
wrong predictions. Therefore, application of detailed kinetic
mechanisms is recommended for modeling CCl4 decomposition under
thermal plasma conditions. 相似文献
9.
Katalin Selmeczi Marius Réglier Gábor Speier Gábor Peintler 《Reaction Kinetics and Catalysis Letters》2004,81(1):143-151
The oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-o-benzoquinone catalyzed by dinuclear copper(II) complexes {[Cu2(L1)(CF3SO3)2(H2O)4]-(CF3SO3)2 (1) and [Cu2(L2O)](CF3SO3)2 (2)| has been investigated in methanol saturated with O2 at ambient temperature. Detailed kinetic studies were carried out and for the treatment the fitting software ZiTa was applied. On the basis of the results in the kinetic studies a possible mechanism of the catalytic reaction is proposed.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
10.
Various two-dimensional (2D) NMR techniques are reported on a bent-core mesogen 4,6-dichloro-1,3-phenylenebis[4'-(9-decenyloxy)-1,1'-biphenyl] carboxylate in its nematic and solid phases in order to unambiguously assign its carbon-13 NMR spectrum. The (13)C chemical shifts from the molecular core were studied as a function of temperature to extract its molecular geometry and orientational order tensor. To this end, the chemical shift anisotropy tensors of some carbon sites were measured in the solid state of this mesogen using a recent method called the separation of undistorted powder patterns by effortless recoupling (SUPER). The average bending angle subtended by the two arms of the bent-core structure is determined to be 148.7 degrees. The C-H dipolar couplings obtained from the separated local field (SLF) experiment for the aromatic rings are used to find the local order parameter tensors. 相似文献