全文获取类型
收费全文 | 2753篇 |
免费 | 81篇 |
国内免费 | 29篇 |
专业分类
化学 | 1701篇 |
晶体学 | 11篇 |
力学 | 56篇 |
数学 | 555篇 |
物理学 | 540篇 |
出版年
2023年 | 11篇 |
2022年 | 14篇 |
2021年 | 105篇 |
2020年 | 41篇 |
2019年 | 58篇 |
2018年 | 58篇 |
2017年 | 49篇 |
2016年 | 102篇 |
2015年 | 74篇 |
2014年 | 112篇 |
2013年 | 194篇 |
2012年 | 180篇 |
2011年 | 191篇 |
2010年 | 131篇 |
2009年 | 126篇 |
2008年 | 153篇 |
2007年 | 165篇 |
2006年 | 155篇 |
2005年 | 159篇 |
2004年 | 130篇 |
2003年 | 87篇 |
2002年 | 65篇 |
2001年 | 28篇 |
2000年 | 28篇 |
1999年 | 32篇 |
1998年 | 26篇 |
1997年 | 34篇 |
1996年 | 25篇 |
1995年 | 34篇 |
1994年 | 25篇 |
1993年 | 25篇 |
1992年 | 20篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 12篇 |
1985年 | 25篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有2863条查询结果,搜索用时 281 毫秒
31.
W. J. Zakrzewski 《Letters in Mathematical Physics》1986,12(4):283-290
We present solutions to the classical equations of motion of a class of P
1-like models. We calculate their action and study their stability properties. 相似文献
32.
Dobrochna Matkowska Maciej Gola Marcin ?nie?ek Piotr Cmoch Krzysztof Staliński 《Journal of organometallic chemistry》2007,692(10):2036-2045
A series of triorganotin hydrides and diorganotin dihydrides containing the optically active 2-(4-isopropyl-2-oxazolinyl)-5-phenyl ligand have been characterized by means of the multinuclear low-temperature NMR investigations, the results of which are discussed. In the corresponding organotin hydrides values of the 1J(1H-117/119Sn) couplings appeared to be temperature dependent, supporting an axial/equatorial position of the hydrogen attached to the tin. 相似文献
33.
Marek Szymo
ski Jacek Ko
odziej Zbigniew Postawa Pawel Czuba Piotr. Piatkowski 《Progress in Surface Science》1995,48(1-4):83-96
Inelastic interactions of electrons with surfaces of ionic crystals result in emission of various particles such as ions, atoms and molecules. We will review such electron-stimulated desorption processes for the particular class of ionic crystals, namely for alkali halides. In this case, a dominant fraction of the emission is in the form of halogen and alkali atoms characterized by a thermal (Maxwellian) spectrum of translational energies. For several alkali halides (potassium and rubidium chlorides, bromides, and iodides), however, a significant part of the halogen atoms is ejected with nonthermal energies, i.e. energies of the order of 0.1 eV. The results of recent systematic studies of angular-resolved kinetic energy distributions of the emitted particles will be reported and current views on the electronic mechanisms of desorption will be described. In particular, it will be shown that the ESD mechanism can be understood in terms of the model involving a surface localisation of the so called “hot-holes” created by electron bombardment of alkali halides. A role of hot holes in ESD processes will further be discussed in relation to very recent experimental results obtained for the KBr crystals doped with In impurities which act as efficient hole traps. 相似文献
34.
Summary Single reverse water-gas shift (RWGS) and dehydrogenation of propane with CO2(DH-CO2) reactions in the presence and absence of the CrOx/SiO2 catalyst have been studied between 673 and 873 K. It was found that the CrOx/SiO2 catalyst is active both in the dehydrogenation of propane and in the RWGS reactions. The obtained results suggest that the
dehydrogenation of propane to propene in the presence of CO2on CrOx/SiO2can be facilitated by the RWGS reaction.</o:p> 相似文献
35.
Acidolytic cleavage of unsymmetrically substituted dithioacetal monoxides, ArCH(SR)S(O)Me has been used to prepare linear unsymmetrical disulfides RSSMe. Disproportionation was suppressed by the addition of a small amount of benzyl mercaptan. The required starting materials were conveniently obtained from appropriately substituted sulfines ArC(=SO)SR and methyl lithium. The following disulfides were prepared: R =n-C4H9 (73.5%), n-C7H15 (78%), Ph (77.3%), AcO(CH2)10 (81.5%).The unsymmetrical dithioacetal PhCH(SEt)SC7H15-n gave upon oxidation with one equivalent of peracid a mixture of two dithioacetal monoxides which on treatment with HClO4 led to three disulfides. This result is discussed in term of the mechanism of acidolysis. 相似文献
36.
Kabatc J Jedrzejewska B Orliński P Paczkowski J 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(1-3):115-125
The photophysical and photochemical properties of p-substitued 2-styryl-ethylbenzothiazolium iodides, possessing different electron-withdrawing or electron-donating groups are described. The dyes were prepared by the condensation of 3-ethyl-2-methylbenzothiazole salts with p-substituted benzaldehydes. The synthesis of suitable substrates is presented as well. We describe here the absorption, emission spectra and the luminescence quantum yield of hemicyanine dyes (SH) measured in 11 different organic solvents of varying polarity. Molecular structure of the synthesized dyes was established by (1)H NMR, electronic absorption and fluorescence spectrometry. The spectral data confirmed that all the compounds exist in E-configuration of their styryl residues. The planar molecular conformation is typical for the compounds with five-membered side aromatic moieties (for example benzothiazole). The compounds possessing N-alkyl substituent in phenyl ring, in contrast to the compounds with other substituents, exhibit low fluorescence quantum yield in THF solution. This indicates that for N-alkyl derivatives the non-radiative processes are much more effective than the radiative ones. The electronic absorption and fluorescence emission spectra of tested dyes demonstrate high sensitivity to the nature of substituent introduced into the aromatic ring. 相似文献
37.
The synthesis of well-defined luminescent organoboron polymers via a novel three-step procedure starting from silylated polystyrene is reported. Highly selective borylation of poly(4-trimethylsilylstyrene) (PS-Si), followed by replacement of the bromine substituents in poly(4-dibromoborylstyrene) (PS-BBr) with substituted thienyl groups (R = H, 3-hexyl, 5-hexyl), and final introduction of the 8-hydroxyquinolato moiety yields a series of new organoboron quinolate polymers in 67-83% isolated yield. The hexyl-substituted polymers are highly soluble and solution-processable yielding thin films that efficiently emit light at 513-514 nm upon excitation at 395 nm. 相似文献
38.
The surface wave produced plasma belongs to a class of RF and microwave induced plasmas. It results from the propagation of an electromagnetic wave which uses the plasma column it sustains and the plasma tube as its sole propagating media. This type of plasma offers several advantages compared to the positive column plasma of dc discharges or to other RF and microwave produced plasmas. Surface wave plasmas require no internal electrodes, and they can be applied over an extremely broad range of wave frequencies (27 MHz to 10 GHz demonstrated) and gas pressures (about 10–4 Torr to a few times the atmospheric pressures). Using the surface wave plasma technique, a large variety of plasma column diameters have been created (0.5–150 mm demonstrated) and no limitation on plasma column length (column up to 6 m long demonstrated) has been found. The surface wave produced plasma is used in elemental analysis and to sustain emission in lasing media. This article is intended as a guide for potential users of surface wave plasmas in the field of plasma processing and plasma chemistry. 相似文献
39.
Kujawa P Moraille P Sanchez J Badia A Winnik FM 《Journal of the American Chemical Society》2005,127(25):9224-9234
The layer-by-layer growth of multilayer assemblies of two polysaccharides, the polyanion hyaluronan (HA) and the polycation chitosan (CH), was investigated using atomic force microscopy (AFM) and surface plasmon resonance (SPR) spectroscopy, with primary emphasis on the effect of the polysaccharide molecular weights on the film thickness and surface morphology. The HA/CH multilayers exhibit an exponential increase of the optical film thickness with the number of deposited bilayers. We show that the multilayer thickness at a given stage depends on the size of both CH, the diffusing polyelectrolyte, and HA, the non-diffusing species. Assemblies (12 bilayers) of high molecular weight polysaccharides (HA, 360,000; CH, 160,000) were twice as thick (approximately 900 nm vs approximately 450 nm) as those obtained with low molecular weight polymers (HA, 30,000; CH, 31,000), as assessed by AFM scratch tests. The exponential growth rate is the same for the high and low molecular weight pairs; the larger film thicknesses observed by SPR and by AFM arising from an earlier onset of the steep exponential growth phase in the case of the high molecular weight pair. In all cases, isolated islets form during the deposition of the first CH layer onto the underlying HA. Upon further film growth, individual islets coalesce into larger vermiculate features. The transition from distinct islands to vermiculate structures depends on the molecular weights of the polysaccharides and the lower molecular weight construct presents larger worm-like surface domains than the high molecular weight pair. 相似文献
40.
Konrad Kowalski Janusz Zakrzewski S?awomir Domaga?a 《Journal of organometallic chemistry》2006,691(18):3902-3908
The synthesis of 1′-ethynyl-2,5-dimethylazaferrocene is reported along with its cyclic voltammetry measurements and the X-ray structure determination of its W(CO)5-complex. Basic coordination and organic chemistry of 1′-ethynyl-2,5-dimethylazaferrocene is also presented via derivatives incorporating cis-Pt(dppe) and Si(Et)3 units. 相似文献