全文获取类型
收费全文 | 1769篇 |
免费 | 43篇 |
国内免费 | 8篇 |
专业分类
化学 | 1189篇 |
晶体学 | 5篇 |
力学 | 69篇 |
数学 | 251篇 |
物理学 | 306篇 |
出版年
2023年 | 8篇 |
2022年 | 12篇 |
2021年 | 47篇 |
2020年 | 32篇 |
2019年 | 28篇 |
2018年 | 24篇 |
2017年 | 24篇 |
2016年 | 51篇 |
2015年 | 26篇 |
2014年 | 45篇 |
2013年 | 75篇 |
2012年 | 82篇 |
2011年 | 103篇 |
2010年 | 58篇 |
2009年 | 64篇 |
2008年 | 97篇 |
2007年 | 122篇 |
2006年 | 105篇 |
2005年 | 95篇 |
2004年 | 106篇 |
2003年 | 60篇 |
2002年 | 67篇 |
2001年 | 29篇 |
2000年 | 30篇 |
1999年 | 17篇 |
1998年 | 17篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 25篇 |
1994年 | 15篇 |
1993年 | 17篇 |
1992年 | 20篇 |
1991年 | 21篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 23篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 20篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1979年 | 22篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 15篇 |
1975年 | 7篇 |
1974年 | 10篇 |
排序方式: 共有1820条查询结果,搜索用时 15 毫秒
31.
Berisio R Granata V Vitagliano L Zagari A 《Journal of the American Chemical Society》2004,126(37):11402-11403
The analysis of factors contributing to the stability of proteins is a subject of intense debate. Particularly challenging is the study of structural proteins, since their function is their structure. Among these is collagen, the key structural component of bones, skin, cartilage, tendons, and other connecting tissues. It is well established that the collagen triple helix is characterized by the presence of hydroxyproline, whose content modulates triple helix thermal stability according to the requirement of the host organism. Because of the complexity and the fibrous nature of collagen, data on the stability and structure of this protein have been mainly obtained by the use of collagen-like polypeptides. On the basis of CD characterization of collagen-like polypeptides we here show that the presence of Hyp at the X position of repeating triplets Hyp-Hyp-Gly stabilizes the triple helix significantly. This extra-stabilization has been ascribed, by using molecular modeling, to the formation of a hydrogen bond between Hyp residues belonging to the X and the Y positions of adjacent chains. This communication also provides a comprehensive interpretation of the ensemble of available data on polypeptides containing proline derivatives. 相似文献
32.
Rosario De Lisi Mario Goffredi Vincenzo Turco Liveri 《Journal of solution chemistry》1981,10(5):351-356
The conductances of dilute aqueous solutions of KCl, KBr, and KI have been measured over the temperature range 2 to 8°C and have been analyzed by the Fuoss-Hsia equation. The ionic Walden products at infinite dilution have been discussed in terms of local viscosity. The temperature dependence of these products suggest that near the temperature of maximum density of water, the structure-breaking ability of these ions changes in a regular way. 相似文献
33.
Alessandro D'Aprano Ines Dorina Donato Vincenzo Turco Liveri 《Journal of solution chemistry》1989,18(8):785-793
Static dielectric constants, refractive indices and viscosities of 1-pentanol +2-methyl-2-butanol mixtures were measured at 5, 25 and 45°C. The results show that the mixing of the two isomers modifies the polarizability and the resistence of viscous flow of the system depending on the composition and temperature. Short range intermolecular interactions producing hetero-alcohol open dimers are considered. 相似文献
34.
Copper bronze catalyzed Heck reaction in ionic liquids 总被引:1,自引:0,他引:1
Heck reaction of aryl iodides and activated aryl bromides catalyzed by copper bronze in tetrabutylammonium bromide as solvent and tetrabutylammonium acetate as base was developed. The effective catalysts are Cu nanoparticles deriving from the reaction of iodobenzene with copper bronze. These nanoparticles are very stable in tetraalkylammonium salts, are easily recycled, and can be stored for months without a loss of catalytic efficiency. [reaction: see text] 相似文献
35.
We present an integrated computational tool, rooted in density functional theory, the polarizable continuum model, and classical molecular dynamics employing spherical boundary conditions, to study the spectroscopic observables of molecules in solution. As a test case, a modified OPLS-AA force field has been developed and used to compute the UV and NMR spectra of acetone in aqueous solution. The results show that provided the classical force fields are carefully reparameterized and validated, the proposed approach is robust and effective, and can also be used by nonspecialists to provide a general and powerful complement to experimental techniques. 相似文献
36.
Sergio Cabani Paolo Gianni Vincenzo Mollica Luciano Lepori 《Journal of solution chemistry》1981,10(8):563-595
The thermodynamic properties G
h
o,H
h
o, and C
p,h
oassociated with the transfer of non-ionic organic compounds from gas to dilute aqueous solution and the limiting partial molar properties C
p
o
,2 and V2
2 of these compounds in water are described through a simple scheme of group contributions. A distinction is made between groups made only of carbon and hydrogen, and functional groups i.e. groups containing at least one atom different from carbon and hydrogen. Each group is assigned a contribution, for each property, through a least squares procedure which utilizes only molecules containing at most one functional group. Finally, for compounds containing more than one functional group, correction parameters are evaluated as the differences between the experimental values and those calculated by means of the group contributions. The different behavior of hydrophilic compared with hydrophobic groups is discussed for the various properties. A rationale for the correction parameters, i.e. for the effects of the interactions among hydrophilic groups on the thermodynamic properties, is attempted. 相似文献
37.
Guido Barone Giuseppina Castronuovo Vittorio Crescenzi Vittorio Elia Eugenio Rizzo 《Journal of solution chemistry》1978,7(3):179-192
In order to clarify some aspects of the hydrophobic interactions, the enthalpies of dilution of monoethylurea, 1,3-dimethylurea,
and 1,3-diethylurea have been determined calorimetrically at 25°C. The calorimetric data, expressed in terms of excess enthalpy,
permit the evaluation of the pair and triplet interaction coefficients. The analyses of these and of the analogous coefficientsg
xx andg
xxx, derived from osmotic data, indicate a driving force favorable to the interactions among the hydrated solute molecules. Nevertheless,
the positive values of theh
xx andh
xxx coefficients seem to suggest that the source of the effect is a rearrangement of the water molecules rather than a direct
association of the solute molecules. There are evidences of a strict correlation between the enthalpic and the entropic effects.
Preliminary data were presented at the International Conferences on Chemical Thermodynamics at Baden (1973) and Montpellier
(1975). The experimental part was carried out at the Istituto Chimico of the University of Trieste.
To whom correspondence should be addressed. 相似文献
38.
Ortona O D'Errico G Vitagliano V Costantino L 《Journal of colloid and interface science》2002,249(2):481-488
Apparent molar relative enthalpies were measured for the nonionic ethoxylated surfactant CH(3)-(CH(2))(5)-(OCH(2)-CH(2))(5)OH (C(6)E(5)) in aqueous solution at constant molality of the ionic surfactant CH(3)-(CH(2))(5)-SO(-)(3)Na(+)(C(6)SNa) at 25 degrees C. The experimental data obtained by a stepwise dilution process allowed evaluation of the C(6)E(5) first interaction parameter at several constant molalities of C(6)SNa. The C(6)E(5) critical micelle composition as a function of the C(6)SNa molality was also estimated. The experimental calorimetric data, together with the mixed micelles composition computed in the past by some of us [Ciccarelli et al., Langmuir 14, 7130 (1998)], allowed computation of the Deltah(Mic) of micellization. The experimental data are compared to those predicted by the ideal solution model and regular solution model of mixed micellization. From a calorimetric study performed on the water-hexanol-C(6)SNa and water-penthaethylene glycol-C(6)SNa model systems, it can be argued that the interactions among the hydrophilic heads in the C(6)E(5)-C(6)SNa mixed micelles prevail on the contribution of the hydrophobic tails in ruling the enthalpic properties of the system. 相似文献
39.
Barone V Bencini A Gatteschi D Totti F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(21):5019-5027
Density functional theory (DFT) was applied to describe the magnetic and electron-transfer properties of dinuclear systems containing the [MnO2Mn]n+ core, with n=0,1,2,3,4. The calculation of the potential energy surfaces (PESs) of the mixed-valence species (n=1,3) allowed the classification of these systems according to the extent of valence localization as Class II compounds, in the Robin-Day classification scheme. The fundamental frequencies corresponding to the asymmetric breathing vibration were also computed. 相似文献
40.
Albano VG Di Serio M Monari M Orabona I Panunzi A Ruffo F 《Inorganic chemistry》2002,41(10):2672-2677
The silver-assisted ligand metathesis reaction involving a platinum(II) complex of formula [PtClMe(N,N-chelate)] with acetonitrile has been investigated. By using a suitably hindered N,N-chelate, an otherwise hardly detectable trinuclear species has been isolated and characterized through X-ray diffractometry. The trinuclear cation consists of two nearly orthogonal [PtCl(Me)(N,N-chelate)] square-planar units entrapping an Ag(+) cation through the chloride ligands that, acting as bidentate, form a linear AgCl(2) unit with two nonequivalent Ag-Cl bonds. The residual acidity of the silver cation is satisfied by one secondary Ag-Pt interaction [Ag-Pt(1) = 2.82 A] in which the platinum atom acts as a donor. Kinetic studies have demonstrated that the silver assistance operates both through a simple associative step and through a pathway in which the above trinuclear complex is an active intermediate. In a noncoordinating solvent the latter species evolves with AgCl loss and formation of a dinuclear Pt,Pt complex showing a rare single chloride bridge. 相似文献