全文获取类型
收费全文 | 601篇 |
免费 | 19篇 |
国内免费 | 2篇 |
专业分类
化学 | 408篇 |
晶体学 | 4篇 |
力学 | 17篇 |
数学 | 72篇 |
物理学 | 121篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 19篇 |
2021年 | 18篇 |
2020年 | 18篇 |
2019年 | 11篇 |
2018年 | 18篇 |
2017年 | 12篇 |
2016年 | 26篇 |
2015年 | 14篇 |
2014年 | 16篇 |
2013年 | 32篇 |
2012年 | 33篇 |
2011年 | 42篇 |
2010年 | 25篇 |
2009年 | 21篇 |
2008年 | 39篇 |
2007年 | 45篇 |
2006年 | 27篇 |
2005年 | 24篇 |
2004年 | 39篇 |
2003年 | 15篇 |
2002年 | 18篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有622条查询结果,搜索用时 14 毫秒
131.
Structure and Bonding in CE5− (E=Al–Tl) Clusters: Planar Tetracoordinate Carbon versus Pentacoordinate Carbon 下载免费PDF全文
Estefanía Ravell Said Jalife Jorge Barroso Mesías Orozco‐Ic Gerardo Hernández‐Juárez Dr. Filiberto Ortiz‐Chi Dr. Sudip Pan Dr. José Luis Cabellos Prof. Gabriel Merino 《化学:亚洲杂志》2018,13(11):1467-1473
The structure, bonding, and stability of clusters with the empirical formula CE5? (E=Al–Tl) have been analyzed by means of high‐level computations. The results indicate that, whereas aluminum and gallium clusters have C2v structures with a planar tetracoordinate carbon (ptC), their heavier homologues prefer three‐dimensional C4v forms with a pentacoordinate carbon center over the ptC one. The reason for such a preference is a delicate balance between the interaction energy of the fifth E atom with CE4 and the distortion energy. Moreover, bonding analysis shows that the ptC systems can be better described as CE4?, with 17‐valence electrons interacting with E. The ptC core in these systems exhibits double aromatic (both σ and π) behavior, but the σ contribution is dominating. 相似文献
132.
133.
Jeffrey S. Quesnel Salvador Moncho Prof. Kai E. O. Ylijoki Gerardo Martin Torres Prof. Edward N. Brothers Prof. Ashfaq A. Bengali Prof. Bruce A. Arndtsen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(42):15107-15118
We describe herein computational studies on the unusual ability of Pd(PtBu3)2 to catalyze formation of highly reactive acid chlorides from aryl halides and carbon monoxide. These show a synergistic role of carbon monoxide in concert with the large cone angle PtBu3 that dramatically lowers the barrier to reductive elimination. The tertiary structure of the phosphine is found to be critical in allowing CO association and the generation of a high energy, four coordinate (CO)(PR3)Pd(COAr)Cl intermediate. The stability of this complex, and the barrier to elimination, is highly dependent upon phosphine structure, with the tertiary steric bulk of PtBu3 favoring product formation over other ligands. These data suggest that even difficult reductive eliminations can be rapid with CO association and ligand manipulation. This study also represents the first detailed exploration of all the steps involved in palladium‐catalyzed carbonylation reactions with simple phosphine ligands, including the key rate‐determining steps and palladium(0) catalyst resting state in carbonylations. 相似文献
134.
Nadia G. Boetti Joris Lousteau Alessandro Chiasera Maurizio Ferrari Emanuele Mura Gerardo C. Scarpignato Silvio Abrate Daniel Milanese 《Journal of luminescence》2012,132(5):1265-1269
Er3+ doped niobic-tungsten–tellurite glasses doped with concentration of Er3+ ion up to 3 wt% were fabricated. The effect of Er3+ doping concentration on thermal stability and optical properties was investigated in order to obtain the most suitable rare earth content for developing 1.5 μm compact fiber amplifier pumped with a commercial telecom 980 nm laser diode. The maximum doping concentration allowed was found to be around 1.77×1020 ions/cm3, for which a broad 1.5 μm emission spectra of 65 nm FWHM and a lifetime of 3.4 ms for the 4I13/2 level was measured. 相似文献
135.
Paula V. Messina Olga Pieroni Bruno Vuano Juan Manuel Ruso Gerardo Prieto Félix Sarmiento 《Journal of inclusion phenomena and macrocyclic chemistry》2010,67(3-4):343-352
The behavior of insoluble calix[n]arene and resorcinol[n]arene derivatives monolayers were studied through the use of a constant surface Langmuir balance based on Axisymmetric Drop Shape Analysis (ADSA). In each case, a stable monolayer was obtained and different transitions (induced for lateral compression) could be identified. Thermodynamic parameters were computed through two dimensional Clausius–Clayperon equations and used to valuate the monolayer stability. A noticeable reduction of thermodynamic parameters occurred at highly tested temperatures (328 and 338 K) for those compounds that had hydrocarbon tails or benzene rings attached to one side of macrocyclic rim. Such fact was related to a monolayer rearrangement where the macrocyclic ring changed from a parallel to a perpendicular orientation. In this orientation the hydrophobic interactions between hydrocarbon chains and benzene rings were maximized. At highly temperature, where vigorous molecular motion existed, those interactions were superior to the stabilization effect through hydrogen bond. 相似文献
136.
Gerardo Camí Juan Server‐Carri Santos Fustero Jos Pedregosa 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):e209-e210
The title compound, C26H32N4O6S2, is a heterocyclic sulfonamide which is a 1,3,4‐thiadiazole derivative. Structural data for this compound are compared with those of related compounds. 相似文献
137.
Gracia C Isidro-Llobet A Cruz LJ Acosta GA Alvarez M Cuevas C Giralt E Albericio F 《The Journal of organic chemistry》2006,71(19):7196-7204
Kahalalide compounds are peptides that are isolated from a Hawaiian herbivorous marine species of mollusc, Elysia rufescens, and its diet, the green alga Bryopsis sp. Kahalalide F and its synthetic analogues are the most promising compounds of the Kahalalide family because they show antitumoral activity. Linear solid-phase syntheses of Kahalalide F have been reported. Here we describe several new improved synthetic routes based on convergent approaches with distinct orthogonal protection schemes for the preparation of Kahaladide analogues. These strategies allow a better control and characterization of the intermediates because more reactions are performed in solution. 相似文献
138.
Given an n-variable mean M defined on a real interval I, an M-affine function is a solution to the functional equation When M is a quasilinear mean, the set of continuous M-affine functions is a Sturm–Liouville family on every compact interval \(\left[ a,b\right] \subseteq I\); i.e., for every \(\alpha ,\beta \in \left[ a,b\right] \), there exists an M-affine function f such that \(f\left( a\right) =\alpha \) and \( f\left( b\right) =\beta \). The validity of the converse statement is explored in this paper and several consequences are derived from this study. New characterizations of quasilinear means and the solution to Eq. (1) under suitable conditions are among the more important ones.
相似文献
139.
In a chemostat, microbial cells reach a steady state condition at which cell biomass production, substrates and the product concentrations remain constant. These features make continuous culture a unique and powerful tool for biological and physiological research. We present a polymer-based microbioreactor system integrated with optical density (OD), pH, and dissolved oxygen (DO) real-time measurements for continuous cultivation of microbial cells. Escherichia coli (E. coli) cells are continuously cultured in a 150 microL, membrane-aerated, well-mixed microbioreactor fed by a pressure-driven flow of fresh medium through a microchannel. Chemotaxisial back growth of bacterial cells into the medium feed channel is prevented by local heating. Using poly(ethylene glycol) (PEG)-grafted poly(acrylic acid) (PAA) copolymer films, the inner surfaces of poly(methyl methacrylate) (PMMA) and poly(dimethylsiloxane) (PDMS) of the microbioreactor are modified to generate bio-inert surfaces resistant to non-specific protein adsorption and cell adhesion. The modified surfaces of microbioreactor effectively reduce wall growth of E. coli for a prolonged period of cultivation. Steady state conditions at different dilution rates are demonstrated and characterized by steady OD, pH, and DO levels. 相似文献
140.
Blanco E Messina P Ruso JM Prieto G Sarmiento F 《The journal of physical chemistry. B》2006,110(23):11369-11376
The complexations between human serum albumin (HSA) and the sodium perfluorooctanoate/sodium octanoate and sodium perfluorooctanoate/sodium dodecanoate systems have been studied by a combination of electrical conductivity, ion-selective electrode, electrophoresis, and spectroscopy measurements. The binary mixtures of the surfactants deviated slightly from ideality. Binding plots revealed the existence of two specific binding sites, the first site being more accessible than the second. Positive cooperative binding has been found, thus revealing the importance of the hydrophobic interactions in both kinds of surfactants. The Gibbs energies of binding per mole of surfactant (DeltaG(nu)) were calculated from the Wyman binding potential where, on the basis of the elevated number of binding sites, a statistical contribution has been included. Initially these energies are large and negative, gradually decreasing as saturation is approached. Changes in the slope of Gibbs energies have been identified with the saturation of the first binding set. These facts denote that the surfactants under study have different favorite adsorption sites along the protein and that the adsorption process of perfluorooctanoate is more closely followed by dodecanoate than by octanoate. Finally, electrophoresis and spectroscopy measurements suggest induced conformational changes on HSA depending on the surfactant mixture as well as the mixed ratio. 相似文献