全文获取类型
收费全文 | 224篇 |
免费 | 11篇 |
专业分类
化学 | 171篇 |
晶体学 | 3篇 |
力学 | 14篇 |
数学 | 29篇 |
物理学 | 18篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 10篇 |
2014年 | 6篇 |
2013年 | 10篇 |
2012年 | 15篇 |
2011年 | 18篇 |
2010年 | 15篇 |
2009年 | 5篇 |
2008年 | 12篇 |
2007年 | 10篇 |
2006年 | 15篇 |
2005年 | 10篇 |
2004年 | 12篇 |
2003年 | 6篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1959年 | 2篇 |
1958年 | 1篇 |
排序方式: 共有235条查询结果,搜索用时 31 毫秒
71.
Mosca A Paleari R Galanello R Sollaino C Perseu L Demartis FR Passarello C Giambona A Maggio A;IFCC Working Group on Standardization of HbA 《Bioelectrochemistry (Amsterdam, Netherlands)》2008,73(2):137-140
The increase of HbA(2) is the most important feature in the identification of beta-thalassemia carriers. However, some carriers are difficult to identify, because the level of HbA(2) is not in the typical range. Few data are available concerning the prevalence of such unusual phenotypes, and knowing their expected prevalence could be helpful in detecting systematic drifts in the analytical systems for HbA(2) quantification. In this study we report a retrospective investigation in two centres with high prevalence of beta-thalassemia. The prevalence of borderline subjects was found to be 2.2 and 3.0%, respectively. The genotypes of a subgroup of these subjects were then analyzed and in about 25% of cases a mutation in the globin genes was identified. We conclude that the occurrence of HbA(2) borderline phenotypes is not a rare event. In order to obtain more accurate HbA(2) measurements the development of an international reference measurement system for HbA(2), based on quantitative peptide mapping, has been recently started. We believe that the innovative approach of our method could also be used as a model to develop accurate quantitative methods for other red cell proteins relevant to the biodynamic properties and the surface electrochemistry of erythrocytes. 相似文献
72.
Morilla ME Rodríguez P Belderrain TR Graiff C Tiripicchio A Nicasio MC Pérez PJ 《Inorganic chemistry》2007,46(22):9405-9414
Thermal reactions between [RuCl2(diene)]n (diene = 2,5-norbornadiene, nbd; 1,5-cyclooctadiene, cod) with an excess of N,N,N',N'-tetramethylethylene diamine (tmeda) afforded derivatives [RuCl2(diene)(tmeda)] (diene = nbd, 1; cod, 2) as a mixture of cis and trans isomers. When thermolysis was performed under H2 mixtures of hydride species [RuCl(H)(diene)(tmeda)] (diene = nbd, 3; cod, 4) and the bis-tmeda adduct trans-[RuCl2(tmeda)2] (5) were obtained in different ratios depending upon the reaction conditions and reaction times. Heating polymeric Ru(II) precursors in toluene in the presence of a 5-fold excess of the bulkier N,N,N',N'-tetraethylethylene diamine (teeda) resulted in a rare diamine dealkylation process with formation of trans-[RuCl2(nbd)(Et2NCH2CH2NHEt)] (6) and trans-[RuCl2(cod)(EtHNCH2CH2NHEt)] (7) in high yields. The presence of N-H functionalities in the coordinated diamine ligands of 6 and 7 was unambiguously established by single-crystal X-ray diffraction studies. The dealkylation process of the teeda ligand seems to proceed intramolecularly as shown by solution NMR studies performed with the soluble Ru(II) precursors trans-[RuCl2(amine)2(diene)] (diene = nbd, amine = morpholine, 9; diene = cod, amine = Et2NH, 10). The above complexes [RuCl2(diene)(diamine)] have been tested as precatalysts in the hydrogenation of ketones both for transfer as well as direct hydrogenation, the latter route being the most effective. 相似文献
73.
A Simple Synthesis of Triangular All‐Metal Aromatics Allowing Access to Isolobal All‐Metal Heteroaromatics
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Yanlan Wang Pierre‐Alexandre Deyris Dr. Tatiana Caneque Florent Blanchard Yanling Li Prof. Franca Bigi Prof. Raimondo Maggi Sebastien Blanchard Dr. Giovanni Maestri Prof. Max Malacria 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(35):12271-12274
A simple synthetic method allows the one‐pot assembly of C3‐symmetric, 44‐core‐valence‐electron, triangular Pd or Pt clusters and their heterobimetallic mixed Pd/Pt analogues. These mixed metal complexes are the first examples of stable triangular all‐metal heteroaromatics. In contrast to traditional heteroaromatic molecules formed combining main‐group elements, they actually retain structural and electronic features of their homonuclear analogues. 相似文献
74.
Donato Cecere Eugenio Giacomazzi Franca R. Picchia Nunzio Arcidiacono Filippo Donato Roberto Verzicco 《Flow, Turbulence and Combustion》2011,86(3-4):667-688
A progress variable/flame surface density/probability density function method has been employed for a Large Eddy Simulation of a CH4/Air turbulent premixed bluff body flame. In particular, both mean and variance of the progress variable are transported and subgrid spatially filtered gradient contributes to model the flame surface density (that introduces the effect of the subgrid flame reaction zone) and to presume a probability density function (that introduces the effect of subgrid fluctuations on chemistry). Chemistry is preliminarly tabulated in terms of laminar premixed flames and enthalpy is included as a new coordinate in their tabulation to take into account heat losses in the flowfield. Then, the PDF is used to build a turbulent flamelet library. The filtered mass, momentum, enthalpy and scalar equations mentioned above are integrated by an explicit scheme using finite differences, 2nd?Corder accurate in space and third order in time, over a cylindrical non-uniform grid using a staggered mesh. The bluff-body geometry is modelled by using the Immersed Boundary Method. The numerical predictions are compared with the available experimental data. 相似文献
75.
Massimiliano D’Arienzo Maurizio Crippa Paolo Gentile Claudio Maria Mari Stefano Polizzi Riccardo Ruffo Roberto Scotti Laura Wahba Franca Morazzoni 《Journal of Sol-Gel Science and Technology》2011,60(3):378-387
Mesoporous Cr or Pt-doped WO3 thin films to be employed as ammonia gas sensors were prepared by a fast one-step sol–gel procedure, based on the use of
triblock copolymer as templating agent. The obtained films were constituted by aggregates of interconnected WO3 nanocrystals (20–50 nm) separated by mesopores with dimensions ranging between 2 and 15 nm. The doping metals, Pt and Cr,
resulted differently hosted in the WO3 mesoporous matrix. Chromium is homogeneously dispersed in the oxide matrix, mainly as Cr(III) and Cr(V) centers, as revealed
by EPR spectroscopy; instead platinum segregated as Pt (0) nanoparticles (4 nm) mainly included inside the WO3 nanocrystals. The semiconductor layers containing Pt nanoclusters revealed, upon exposure to NH3, remarkable electrical responses, much higher than Cr-doped and undoped layers, particularly at low ammonia concentration
(6.2 ppm). This behavior was attributed to the presence of Pt nanoparticles segregated inside the semiconductor matrix, which
act as catalysts of the N–H bond cleavage, decreasing the activation barrier in the ammonia dissociation. The role of the
mesoporous structure in influencing the chemisorption and the gas diffusion in the WO3 matrix appeared less decisive than the electronic differences between the two examined doping metals. The overall results
suggest that a careful combination between mesoporous architecture and metal doping can really promote the electrical response
of WO3 toward ammonia. 相似文献
76.
Floris FM 《The Journal of chemical physics》2012,136(11):116102
77.
Caronna T Castiglione F Famulari A Fontana F Malpezzi L Mele A Mendola D Sora IN 《Molecules (Basel, Switzerland)》2012,17(1):463-479
Quantum mechanics density functional calculations provided gas-phase electron distributions and proton affinities for several mono- and diaza[5]helicenes; computational results, together with experimental data concerning crystal structures and propensity to methylation of the nitrogen atom(s), provide a basis for designing azahelicene complexes with transition metal ions. 相似文献
78.
Franca Podo George Némethy Pietro L. Indovina Lajos Radics Vincenza Viti 《Molecular physics》2013,111(2):521-539
As a theoretical analysis of the conformational equilibria of ethylene glycol, methoxyethanol and dimethoxyethane, the energy of each stable conformational isomer (rotamer) of these molecules was calculated for various temperatures and solvent dielectric constants. Classical semi-empirical potential functions were used. Besides intrinsic potentials for rotation about single bonds, intramolecular dispersion and repulsive interaction, dipole-dipole interaction and hydrogen bonding energies were included. Interaction with the solvent was considered only in terms of a continuous dielectric medium interacting with the local dipoles and quadrupoles of the molecule. For each rotamer, the dihedral angles giving the lowest energy were determined. From the energies of each rotamer, Boltzmann distributions of populations were obtained, and total concentrations were calculated in various physically distinguishable states, e.g. those with and without internal hydrogen bonds, or those in which the central C-C bond takes a trans or a gauche conformation. It is shown that the equilibrium constants, K HB and K TG, for these two cases are not identical. While changes in the dielectric constant may alter strongly the geometries and energies of individual rotamers, their effect on the average geometries and on the two equilibrium constants is small. The same is true of temperature changes, and is due to the presence of several rotamers in each of the physical states considered. Thus the small temperature dependence of some observed physical properties is shown to be consistent with the distribution of molecules over several conformational states. In solution, the fraction of ethylene glycol molecules with two free OH groups (i.e. without an intramolecular hydrogen bond) is predicted to be at least 20 per cent. This shows that the presence of three-dimensional hydrogen-bonded structures in the liquid, which we propose, is possible in principle. 相似文献
79.
80.
Michela Alfieri Iride Mascheretti Romo A. Dougu Kentsop Roberto Consonni Franca Locatelli Monica Mattana Gianluca Ottolina 《Molecules (Basel, Switzerland)》2021,26(17)
Lignans are the main secondary metabolites synthetized by Linum species as plant defense molecules. They are also valuable for human health, in particular, for their potent antiviral and antineoplastic properties. In this study, the adventitious root cultures of three Linum species (L. flavum, L. mucronatum and L. dolomiticum) were developed to produce aryltetralin lignans. The effect of two elicitors, methyl jasmonate and coronatine, on aryltetralin lignans production was also evaluated. The adventitious root cultures from L. dolomiticum were obtained and analyzed for the first time and resulted as the best producer for all the aryltetralins highlighted in this system: Podophyllotoxin, 6-methoxypodophyllotoxin and 6-methoxypodophyllotoxin-7-O-β-glucoside, the last showing a productivity of 92.6 mg/g DW. The two elicitors differently affected the production of the 6-methoxypodophyllotoxin and 6-methoxypodophyllotoxin-7-O-β-glucoside. 相似文献