全文获取类型
收费全文 | 576篇 |
免费 | 23篇 |
国内免费 | 3篇 |
专业分类
化学 | 346篇 |
晶体学 | 3篇 |
力学 | 21篇 |
数学 | 80篇 |
物理学 | 152篇 |
出版年
2023年 | 4篇 |
2022年 | 14篇 |
2021年 | 11篇 |
2020年 | 19篇 |
2019年 | 9篇 |
2018年 | 23篇 |
2017年 | 11篇 |
2016年 | 26篇 |
2015年 | 10篇 |
2014年 | 22篇 |
2013年 | 31篇 |
2012年 | 30篇 |
2011年 | 41篇 |
2010年 | 23篇 |
2009年 | 22篇 |
2008年 | 28篇 |
2007年 | 24篇 |
2006年 | 31篇 |
2005年 | 34篇 |
2004年 | 18篇 |
2003年 | 16篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1982年 | 8篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1958年 | 2篇 |
1941年 | 2篇 |
1935年 | 3篇 |
1934年 | 2篇 |
1932年 | 3篇 |
排序方式: 共有602条查询结果,搜索用时 0 毫秒
51.
César Menor‐Salván Dr. Dra. Marta Ruiz‐Bermejo Marcelo I. Guzmán Dr. Susana Osuna‐Esteban Sabino Veintemillas‐Verdaguer Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(17):4411-4418
From urea to nucleobases : Freeze–thaw cycles in urea ( 1 ) solutions under methane/nitrogen atmospheres lead, with application of an energy source, to the synthesis of pyrimidines (mainly cytosine ( 2 ) and uracil ( 3 )), triazines (such as cyanuric acid ( 4 )), and adenine. This synthesis appears to be dependent on the atmosphere and the freezing conditions. At room temperature, hydantoin ( 5 ) is obtained. However, a freezing urea/water system subjected to an energy source under an inert atmosphere generates s‐triazines.
52.
Julieta I. Paez Ariel L. Cappelletti Ana M. Baruzzi Verónica Brunetti Miriam C. Strumia 《Macromolecular Symposia》2010,290(1):37-45
Summary: The spontaneous adsorption of the dendron 3,5-Bis (3,5-dinitrobenzoylamino) benzoic acid (D-NO2) onto gold and carbon electrodes produced conductive surfaces with electroactive chemical functions. A comparative electrochemical behavior of both electrodes after dendron immobilization led us to conclude that the self-assembly of D-NO2 on carbon is faster and stronger. Considering this advantage, the surface of magnetic maghemite nanoparticles (MNPs) was modified using D-NO2. Firstly, MNPs were modified with APS as silane coupling agent and afterwards, D-NO2 was covalently attached to the surface, achieving nitro-functionalized MNPs. Subsequently, the immobilization of these modified MNPs onto glassy carbon surfaces was explored to generate a novel platform promising for biosensors development. 相似文献
53.
Dr. Sung Sakong Christian Mosch Ariel Lozano Dr. H. Fabio Busnengo Prof. Dr. Axel Groß 《Chemphyschem》2012,13(15):3467-3471
Any technologically important chemical reaction typically involves a number of different elementary reaction steps consisting of bond‐breaking and bond‐making processes. Usually, one assumes that such complex chemical reactions occur in a step‐wise fashion where one single bond is made or broken at a time. Using first‐principles calculations based on density functional theory we show that the barriers of rate‐limiting steps for technologically relevant surface reactions are significantly reduced if concerted reaction mechanisms are taken into account. 相似文献
54.
E. T. Romero Guzmán M. V. Esteller Alberich E. Ordoñez Regil 《Journal of Radioanalytical and Nuclear Chemistry》2002,254(3):509-517
Phosphate fertilizers contain approximately 200 mg.kg-1 of uranium. The uranium and phosphate can move through the vadose zone and reach groundwater. Therefore, the knowledge of the ways in which these two elements are distributed, their partition relationships and their mobility behavior is of great interest. In order to study the latter, suction cup samplers, intended to collect soil water at different depths, were installed in an experimental site in a high plain of Mexico, where corn is cultivated and phosphate fertilizers are systematically applied. It was observed that the vadose zone contains high concentrations of uranium (1-50 mg.kg-1) and phosphates (22-33 mg.kg-1), which decrease at greater depths. Uranium concentration in the soil water varies between 10 and 3 mg.l-1 and phosphates between 1 and 0.3 mg.l-1. Their evolution throughout the profile of the vadose zone is determined by the decrease in concentrations, due to the physico-chemical processes involved. 相似文献
55.
An amperometric flow-injection method for the determination of antithyroid drugs such as 6-methyl-2-thiouracil (MTU) using a carbon fiber cylindrical microelectrode-based detector is reported. A home-made flow-cell specially adapted for working with cylindrical microelectrodes ranging between 4 and 10 mm in length was used for this purpose. Methanol containing 0.05 mol l(-1) tetrabutylammonium perchlorate as the supporting electrolyte was employed, and a potential of +1.6 V was selected for the amperometric detection of MTU. No cleaning or electrode surface regeneration of the fiber was necessary during the whole working day. A limit of detection of 2.6x10(-7) mol l(-1) (37 mug MTU l(-1)) was achieved. The method was applied to the determination of MTU in spiked feed samples (peas and corn flour), at the 142 mug g(-1) level. The procedure involved the extraction of the drug in methanol, a clean-up step using Florisil cartridges and the use of the standard additions method. Recoveries of 81+/-6 and 85+/-8% were obtained for peas and corn flour, respectively. 相似文献
56.
Ariel M. Sarotti 《Tetrahedron letters》2004,45(44):8203-8206
A two-step general approach to a new chiral auxiliary starting from levoglucosenone is reported. The compound is obtained by a [4+2] cycloaddition reaction with anthracene followed by a diastereoselective reduction of the C-2 keto function in high overall yield. The auxiliary has been used as chiral template in an asymmetric Diels-Alder reaction of the corresponding acrylic ester derivative with cyclopentadiene and shown to be efficient for asymmetric induction. 相似文献
57.
58.
The π‐Back‐Bonding Modulation and Its Impact in the Electronic Properties of CuII Antineoplastic Compounds: An Experimental and Theoretical Study 下载免费PDF全文
Juan Carlos García‐Ramos Dr. Rodrigo Galindo‐Murillo Araceli Tovar‐Tovar Ana Luisa Alonso‐Saenz Virginia Gómez‐Vidales Dr. Marcos Flores‐Álamo Dr. Luis Ortiz‐Frade Dr. Fernando Cortes‐Guzmán Dr. Rafael Moreno‐Esparza Prof. Antonio Campero Prof. Lena Ruiz‐Azuara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(42):13730-13741
59.
Eric Iván Sánchez‐Flores Rodrigo Chávez‐Calvillo Todd A. Keith Gabriel Cuevas Tomás Rocha‐Rinza Fernando Cortés‐Guzmán 《Journal of computational chemistry》2014,35(10):820-828
The topological analysis of the electron density for electronic excited states under the formalism of the quantum theory of atoms in molecules using time‐dependent density functional theory (TDDFT) is presented. Relaxed electron densities for electronic excited states are computed by solving a Z‐vector equation which is obtained by means of the Sternheimer interchange method. This is in contrast to previous work in which the electron density for excited states is obtained using DFT instead of TDDFT, that is, through the imposition of molecular occupancies in accordance with the electron configuration of the excited state under consideration. Once the electron density of the excited state is computed, its topological characterization and the properties of the atoms in molecules are obtained in the same manner that for the ground state. The analysis of the low‐lying singlet and triplet vertical excitations of CO and C6H6 are used as representative examples of the application of this methodology. Altogether, it is shown how this procedure provides insights on the changes of the electron density following photoexcitation and it is our hope that it will be useful in the study of different photophysical and photochemical processes. © 2014 Wiley Periodicals, Inc. 相似文献
60.
Dr. Elena Riva Dr. Ina Wilkening Silvia Gazzola W. M. Ariel Li Dr. Luke Smith Prof. Peter F. Leadlay Dr. Manuela Tosin 《Angewandte Chemie (International ed. in English)》2014,53(44):11944-11949
A library of functionalized chemical probes capable of reacting with ketosynthase‐bound biosynthetic intermediates was prepared and utilized to explore in vivo polyketide diversification. Fermentation of ACP mutants of S. lasaliensis in the presence of the probes generated a range of unnatural polyketide derivatives, including novel putative lasalocid A derivatives characterized by variable aryl ketone moieties and linear polyketide chains (bearing alkyne/azide handles and fluorine) flanking the polyether scaffold. By providing direct information on microorganism tolerance and enzyme processing of unnatural malonyl‐ACP analogues, as well as on the amenability of unnatural polyketides to further structural modifications, the chemical probes constitute invaluable tools for the development of novel mutasynthesis and synthetic biology. 相似文献