全文获取类型
收费全文 | 219篇 |
免费 | 10篇 |
专业分类
化学 | 189篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 18篇 |
物理学 | 19篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 11篇 |
2012年 | 16篇 |
2011年 | 14篇 |
2010年 | 6篇 |
2009年 | 8篇 |
2008年 | 18篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 8篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2002年 | 11篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1970年 | 1篇 |
1908年 | 1篇 |
1901年 | 1篇 |
1873年 | 1篇 |
排序方式: 共有229条查询结果,搜索用时 15 毫秒
81.
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
82.
Dr. Saibal Bera Dr. Satyajit Das Prof. Dr. Manuel Melle-Franco Prof. Dr. Aurelio Mateo-Alonso 《Angewandte Chemie (International ed. in English)》2023,62(5):e202216540
Organic cages have gained increasing attention in recent years as molecular hosts and porous materials. Among these, barrel-shaped cages or molecular nanobarrels are promising systems to encapsulate large hosts as they possess windows of the same size as their internal cavity. However, these systems have received little attention and remain practically unexplored despite their potential. Herein, we report the design and synthesis of a new trigonal prismatic organic nanobarrel with two large triangular windows with a diameter of 12.7 Å optimal for the encapsulation of C60. Remarkably, this organic nanobarrel shows a high affinity for C60 in solvents in which C60 is virtually insoluble, providing stable solutions of C60. 相似文献
83.
Adsorption of volatile organic compounds onto carbon nanotubes, carbon nanofibers, and high-surface-area graphites 总被引:1,自引:0,他引:1
The adsorption of different alkanes (linear and cyclic), aromatics, and chlorohydrocarbons onto different nonmicroporous carbons--multiwalled carbon nanotubes (CNTs), carbon nanofibers (CNFs), and high-surface-area graphites (HSAGs)--is studied in this work by inverse gas chromatography (IGC). Capacity of adsorption was derived from the isotherms of adsorption, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined from chromatographic retention data. HSAGs present the highest adsorption capacity, followed by CNTs and CNFs (although CNTs present an intermediate surface area between the two HSAG studied). Among the different adsorbates tested, benzene exhibits the highest adsorption capacity, and the same trend is observed in the enthalpy of adsorption. From surface free energy data, enthalpies of adsorption of polar compounds were divided into dispersive and specific contributions. The interactions of cyclic (benzene and cyclohexane) and chlorinated compounds (trichloroethylene, tetrachloroethylene, and chloroform) with the surfaces are mainly dispersive over all the carbons tested, CNTs being the material with the highest dispersive contribution, as was deduced also from the entropy parameter. Adsorption parameters were correlated with morphological and chemical properties of the materials. 相似文献
84.
Lilian F. Berti Aurelio R. L. Oliveira Carla T. L. S. Ghidini 《Mathematical Methods of Operations Research》2017,85(1):61-75
In this paper, we present a proposal for a variation of the predictor–corrector interior point method with multiple centrality corrections. The new method uses the continued iteration to compute a new search direction for the predictor corrector method. The purpose of incorporating the continued iteration is to reduce the overall computational cost required to solve a linear programming problem. The computational results constitute evidence of the improvement obtained with the use of this technique combined with the interior point method. 相似文献
85.
The substrate-controlled RhI-catalyzed conjugate addition of aryl- and alkenylboronic acids to alpha,beta-unsaturated esters which bear gamma- and delta-oxygen substituents takes place in a highly anti diastereoselective fashion either when using gamma-hydroxyl unprotected starting materials or when the gamma-oxygen substituent is protected with a nonbulky group. The delta-oxygen substituent plays a role in the stereoselectivity of the reaction, and better results are obtained when this OH-group is protected. 相似文献
86.
Juan P. Mora-Fuentes Ilias Papadopoulos Dominik Thiel Dr. Roberto Álvarez-Boto Dr. Diego Cortizo-Lacalle Prof. Dr. Timothy Clark Prof. Dr. Manuel Melle-Franco Prof. Dr. Dirk M. Guldi Prof. Dr. Aurelio Mateo-Alonso 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(3):1129-1133
Singlet fission has emerged as a promising strategy to avoid the loss of extra energy through thermalization in solar cells. A family of dimers consisting of nitrogen-doped pyrene-fused acenes that undergo singlet fission with triplet quantum yields as high as 125 % are presented. They provide new perspectives for nitrogenated polycyclic aromatic hydrocarbons and for the design of new materials for singlet fission. 相似文献
87.
Ducruet JM Serrano A Roncel M Ortega JM 《Journal of photochemistry and photobiology. B, Biology》2011,104(1-2):301-307
The microalgae Chlamydomonas reinhardtii and Chlorella sp. CCAP 211/84 were grown autotrophically and mixotrophically and their thermoluminescence emissions were recorded above 0 °C after excitation by 1, 2 or 3 xenon flashes or by continuous far-red light. An oscillation of the B band intensity according to the number of flashes was always observed, with a maximum after 2 flashes, accompanied by a downshift of the B band temperature maximum in mixotrophic compared to autotrophic grown cells, indicative of a dark stable pH gradient. Moreover, new flash-induced bands emerged in mixotrophic Chlamydomonas grown cells, at temperatures higher than that of the B band. In contrast to the afterglow band observed in higher plants, in Chlamydomonas these bands were not inducible by far-red light, were fully suppressed by 2 μM antimycin A, and peaked at different temperatures depending on the flash number and growth stage, with higher temperature maxima in cells at a stationary compared to an exponential growth stage. These differences are discussed according to the particular properties of cyclic electron transfer pathways in C. reinhardtii. 相似文献
88.
Mixed micelles of n-octyl-β-D-thioglucoside (OTG) and octaethylene-glycol monododecyl ether (C(12)E(8)), two non-ionic surfactants belonging to the alkyl glucosides and polyoxyethylene alkyl ether families, respectively, were investigated by using light scattering and fluorescence probe techniques. From the determination of the critical micelle concentration (cmc), by the well-established pyrene 1:3 ratio method, it was found that the mixed system behaves ideally, the micellization process being clearly controlled by the ethoxylated surfactant. The micellar hydrodynamic radius as a function of temperature, composition and concentration was obtained by dynamic light scattering measurements. It was observed that the micellar size increases with temperature, this growth being more pronounced as the relative proportion of the ethoxylated surfactant was increased. The behavior of the micellar size with the total surfactant concentration was also found to be dependent on temperature and composition. The clouding temperature, characteristic of the ethoxylated surfactants, was increased with the addition of the sugar surfactant. Lastly, possible structural changes in the micellar palisade layer were examined by steady-state fluorescence anisotropy in conjunction with time-resolved fluorescence studies with the hydrophobic probe coumarin 6 (C6). The obtained results indicate that the participation of the ethoxylated surfactant induces a slightly more polar palisade layer, whereas the probe carries out a faster rotational reorientation as a result of a less compact environment. All these observations were attributed to the different structure of the head groups of both surfactants and, as a consequence, to their different hydration. 相似文献
89.
María D. Gonzalez-Lima Aurelio R. L. Oliveira Danilo E. Oliveira 《Computational Optimization and Applications》2013,56(3):573-597
We introduce an efficient and robust proposal for solving linear systems arising at each iteration of primal-dual interior-point methods for linear programming. Our proposal is based on the stable system presented by Gonzalez-Lima et al. (Comput. Opt. Appl. 44:213–247, 2009). Using similar techniques as those employed in the splitting preconditioner introduced by Oliveira and Sorensen (Linear Algebra Appl. 394:1–24, 2005) we are able to express the stable system matrix in block form such that the diagonal blocks are nonsingular diagonal matrices and the off-diagonal blocks are matrices close to zero when the iterates are close to the solution set of the linear programming problem. For degenerate problems a perturbation of the diagonal is added. We use a low-cost fixed iterative method to solve this system. Numerical experiments have shown that our approach leads to very accurate solutions for the linear programming problem. 相似文献
90.
Rosario M. P. Colodrero Aurelio Cabeza Dr. Pascual Olivera‐Pastor Dr. Antonia Infantes‐Molina Dr. Eleni Barouda Konstantinos D. Demadis Prof. Miguel A. G. Aranda Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(27):6612-6618
Breathe easy : Reversible H2O and NH3 gas uptake by 2D calcium tetraphosphonates (see figure) is accompanied by framework structural changes similar to those previously reported for some carboxylate‐based hybrids. This breathing mechanism is accompanied by a volume increase of 55 %, while maintaining the topology and crystallinity of the material.