全文获取类型
收费全文 | 724篇 |
免费 | 5篇 |
国内免费 | 3篇 |
专业分类
化学 | 406篇 |
晶体学 | 1篇 |
力学 | 79篇 |
数学 | 154篇 |
物理学 | 92篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 17篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 11篇 |
2017年 | 3篇 |
2016年 | 17篇 |
2015年 | 16篇 |
2014年 | 15篇 |
2013年 | 24篇 |
2012年 | 37篇 |
2011年 | 43篇 |
2010年 | 33篇 |
2009年 | 25篇 |
2008年 | 39篇 |
2007年 | 44篇 |
2006年 | 30篇 |
2005年 | 34篇 |
2004年 | 33篇 |
2003年 | 29篇 |
2002年 | 24篇 |
2001年 | 10篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 12篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1973年 | 3篇 |
1969年 | 4篇 |
排序方式: 共有732条查询结果,搜索用时 0 毫秒
11.
The relative permittivity of 1,2-dimethoxyethane and N,N-dimethylformamide mixtures from −10 to 40°C
Gianni Goldoni Luigi Marcheselli Andrea Marchetti Lorenzo Tassi Giuseppe Tosi 《Journal of solution chemistry》1992,21(9):953-962
Binary solutions of N,N-dimethylformamide and 1,2-dimethoxyethane have been investigated by means of dielectric measurements at temperatures ranging from –10 to +40°C, and for nine mixtures covering the whole miscibility field expressed by the mole fraction of one component (0X11). The experimental data were used to study the dependence of on T and X1, of the type = (T), = (X1), and = (T,X1). Further, the excess mixing function E has been evaluated in order to identify particular patterns of interaction between unlike molecules and any other factor that could modify such patterns. The minimum in the E vs. composition plots suggests the formation of an adduct of stoichiometric ratio DMFDME=11 at all the investigated temperatures. 相似文献
12.
Graziella Tocco Michela Begala Giovanna Delogu Carmen Picciau Gianni Podda 《Tetrahedron letters》2004,45(37):6909-6913
In the presence of catalytic amount of indium(III) chloride (10 mol %), 2,2′-dihydroxybiphenyl and bis(2-hydroxyphenyl)methane react quickly, without using any solvent, with ketones or β-keto esters possessing at least one hydrogen atom in α to the ketone-carbonyl group, to afford some new dibenzo(d,f)(1,3)dioxepines and some 12H-dibenzo(d,g)(1,3)dioxocin derivatives, respectively. 相似文献
13.
Luca Bernazzani Maria Rita Carosi Celia Duce Paolo Gianni Vincenzo Mollica 《Journal of solution chemistry》2006,35(11):1567-1585
Excess molar volumes, V
m
E, over the whole composition range for binary mixtures of 1-butanol, 2-butanol, and 2-methyl-2-propanol + 1-octanol, or 2-octanol, or di-n-butyl ether, or n-hexylacetate were determined at 298.15 K from density measurements carried out with a vibrating-tube densimeter. Small V
m
E values, both positive and negative, are displayed by mixtures containing 1- or 2-octanol, whereas positive and larger values are always found for mixtures containing dibutyl ether and hexylacetate. These results can be justified in terms of H-bonding interactions and/or steric hindrance due to the branched alkyl chains. Partial molar volumes at infinite dilution of the isomeric butanols in the C8 compounds were also calculated from the apparent molar volumes in dilute solution. The solute-solvent interactions and the effects of the local organisation of the solvent around the butanol molecules were discussed using the void and cavity volumes as different estimates of the intrinsic volume of the molecules. The volumetric behavior of butanols seems to be determined by the solute-solvent interactions rather than packaging effects. 相似文献
14.
Galaverna G Sforza S Tedeschi T Corradini R Dossena A Marchelli R 《Electrophoresis》2003,24(15):2698-2703
Direct chiral separation of chiral peptide nucleic acid (PNA) monomers has been achieved for the first time by capillary electrophoresis (CE) with charged cyclodextrins as chiral selectors added to the electrophoretic buffer. Selectively modified 6-deoxy-6-N-histamino-beta-cyclodextrin and sulfobutyl ether-beta-CD were successfully used as chiral selectors for the enantiomeric separation of chiral monomers based on different aminoethylamino acids bearing thymine or adenine as nucleobases. Chiral separations were obtained at low selector concentrations (1-3 mM) with good enantioselectivity and resolution factors. Separations were optimized as a function of pH in order to exploit the effect of the electrostatic interactions between the oppositely charged selector and selectand. The method has been applied to the analysis of the enantiomeric excess of chiral monomers used for the solid phase synthesis of chiral PNA oligomers. CE chiral analysis showed that a very high enantiomeric purity was generally achieved in the synthesis of all monomers, except for histidine and aspartic acid based monomers in which ca. 10% of the "wrong" enantiomer was always present. 相似文献
15.
Stańczak P Valensin D Juszczyk P Grzonka Z Valensin G Bernardi F Molteni E Gaggelli E Kozłowski H 《Chemical communications (Cambridge, England)》2005,(26):3298-3300
The interaction between the single hexarepeat unit of chicken prion protein [ChPrP(54-59)] and Cu(II) was investigated by NMR, finding different coordination modes for the trans/trans and cis/trans isomers. 相似文献
16.
Fermo P Cariati F Pozzi A Tettamanti M Collina E Pitea D 《Fresenius' Journal of Analytical Chemistry》2000,366(3):267-272
The synergy of the micro FT-IR (Fourier Transform-Infrared) and SEM-EDX (Scanning Electron Microscopy-Energy Dispersive X-ray) techniques has been shown to be particularly helpful and effective for the characterization of inorganic compounds in fly ashes. The experimental data obtained by these techniques have been interpreted in comparison with those of other techniques. The presence of calcium carbonate, some sulfates, ammonium nitrate, calcium hydrogen phosphate, some chlorides, some oxides and aluminium silicates have been verified. 相似文献
17.
Valensin D Luczkowski M Mancini FM Legowska A Gaggelli E Valensin G Rolka K Kozlowski H 《Dalton transactions (Cambridge, England : 2003)》2004,(9):1284-1293
Potentiometric and spectroscopic data have shown that octarepeat dimer and tetramer are much more effective ligands for Cu(II) ions than simple octapeptide. Thus, the whole N-terminal segment of prion protein due to cooperative effects, could be more effective in binding of Cu(II) than simple peptides containing a His residue. The gain of the Cu(II) binding by longer octarepeat peptides derives from the involvement of up to four imidazoles in the coordination of the first Cu(II) ion. This type of binding increases the order of the peptide structure, which allows successive metal ions for easier coordination. 相似文献
18.
Giulia DArrigo Eleonora Gianquinto Giulia Rossetti Gabriele Cruciani Stefano Lorenzetti Francesca Spyrakis 《Molecules (Basel, Switzerland)》2021,26(6)
Flavonoids are plant bioactives that are recognized as hormone-like polyphenols because of their similarity to the endogenous sex steroids 17β-estradiol and testosterone, and to their estrogen- and androgen-like activity. Most efforts to verify flavonoid binding to nuclear receptors (NRs) and explain their action have been focused on ERα, while less attention has been paid to other nuclear and non-nuclear membrane androgen and estrogen receptors. Here, we investigate six flavonoids (apigenin, genistein, luteolin, naringenin, quercetin, and resveratrol) that are widely present in fruits and vegetables, and often used as replacement therapy in menopause. We performed comparative computational docking simulations to predict their capability of binding nuclear receptors ERα, ERβ, ERRβ, ERRγ, androgen receptor (AR), and its variant ART877A and membrane receptors for androgens, i.e., ZIP9, GPRC6A, OXER1, TRPM8, and estrogens, i.e., G Protein-Coupled Estrogen Receptor (GPER). In agreement with data reported in literature, our results suggest that these flavonoids show a relevant degree of complementarity with both estrogen and androgen NR binding sites, likely triggering genomic-mediated effects. It is noteworthy that reliable protein–ligand complexes and estimated interaction energies were also obtained for some suggested estrogen and androgen membrane receptors, indicating that flavonoids could also exert non-genomic actions. Further investigations are needed to clarify flavonoid multiple genomic and non-genomic effects. Caution in their administration could be necessary, until the safe assumption of these natural molecules that are largely present in food is assured. 相似文献
19.
N.Tz. Dintcheva S. AlessiR. Arrigo G. PrzybytniakG. Spadaro 《Radiation Physics and Chemistry》2012,81(4):432-436
In this paper two systems, polyethylene (LDPE) and polyethylene/commercial organo-modified montmorillonite (LDPE/OMMT) nanocomposite, were subjected to e-beam irradiation at different doses and both the molecular modifications and mechanical properties have been investigated through solubility, FT-IR, calorimetric and tensile tests. Moreover, in some of the irradiated systems photo-oxidation aging was performed and its effects were studied. The results show an enhancement with irradiation of the positive effect of the nano-filler loading, related to the increase of the mechanical properties, due to the increase of the nano-filler polymer interaction.Nevertheless calorimetric and FT-IR data indicate that the well known reduction of LDPE/OMMT nanocomposite resistance to photo-oxidation ageing, with respect to LDPE, is amplified by ionizing radiation. 相似文献
20.