全文获取类型
收费全文 | 1655篇 |
免费 | 34篇 |
国内免费 | 5篇 |
专业分类
化学 | 1100篇 |
晶体学 | 15篇 |
力学 | 73篇 |
数学 | 291篇 |
物理学 | 215篇 |
出版年
2023年 | 13篇 |
2021年 | 20篇 |
2020年 | 27篇 |
2019年 | 25篇 |
2018年 | 21篇 |
2017年 | 19篇 |
2016年 | 47篇 |
2015年 | 29篇 |
2014年 | 34篇 |
2013年 | 77篇 |
2012年 | 71篇 |
2011年 | 106篇 |
2010年 | 62篇 |
2009年 | 48篇 |
2008年 | 83篇 |
2007年 | 92篇 |
2006年 | 83篇 |
2005年 | 84篇 |
2004年 | 77篇 |
2003年 | 65篇 |
2002年 | 48篇 |
2001年 | 14篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 7篇 |
1997年 | 15篇 |
1996年 | 21篇 |
1995年 | 14篇 |
1994年 | 20篇 |
1993年 | 20篇 |
1992年 | 21篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 22篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 11篇 |
1985年 | 28篇 |
1984年 | 31篇 |
1983年 | 20篇 |
1982年 | 20篇 |
1981年 | 18篇 |
1980年 | 21篇 |
1979年 | 18篇 |
1978年 | 16篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1975年 | 11篇 |
1974年 | 18篇 |
1973年 | 9篇 |
排序方式: 共有1694条查询结果,搜索用时 656 毫秒
1.
Consigli Giorgio Hitaj Asmerilda Mastrogiacomo Elisa 《Computational Management Science》2019,16(1-2):129-154
Computational Management Science - A sensitivity analysis of the impact of cumulative prospect theory (CPT) parameters on a Mean/Risk efficient frontier is performed through a simulation procedure,... 相似文献
2.
Marina Sicignano Dr. Rosaria Schettini Luisa Sica Giovanni Pierri Prof. Dr. Francesco De Riccardis Prof. Dr. Irene Izzo Dr. Bholanath Maity Dr. Yury Minenkov Prof. Dr. Luigi Cavallo Dr. Giorgio Della Sala 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(29):7131-7141
The first highly enantioselective arylogous Michael reaction (AMR) of 3-unsubstituted phthalides has been described. This phase-transfer methodology, which uses catalytic amounts of KOH/18-crown-6 catalyst in mesitylene in the presence of N,O-bis(trimethylsilyl)acetamide (BSA), gives access to a broad range of 3-monosubstituted phthalides with high levels of syn diastereoselectivity and good yields, starting from 3-unsubstituted derivatives and diverse α,β-unsaturated carbonyl compounds. The reaction also applies to unactivated 3-alkyl phthalides to afford 3,3-dialkyl derivatives. A plausible mechanism has been suggested. DFT analysis of possible transition states gives a rationale of the high syn diastereoselectivity observed and its correlation with the solvent's dielectric constant. 相似文献
3.
4.
Oncogenic MicroRNAs Biogenesis as a Drug Target: Structure–Activity Relationship Studies on New Aminoglycoside Conjugates 下载免费PDF全文
5.
6.
In this paper we analyse some questions concerning trees on κ, both for the countable and the uncountable case, and the connections with Cohen reals. In particular, we provide a proof for one of the implications left open in [6, Question 5.2] about the diagram for regularity properties. 相似文献
7.
Alessio Melli Simone Potenti Dr. Mattia Melosso Dr. Sven Herbers Dr. Lorenzo Spada Dr. Andrea Gualandi Kevin G. Lengsfeld Prof. Luca Dore Philipp Buschmann Prof. Pier Giorgio Cozzi Prof. Jens-Uwe Grabow Prof. Vincenzo Barone Prof. Cristina Puzzarini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):15016-15022
Phenylmethanimine is an aromatic imine with a twofold relevance in chemistry: organic synthesis and astrochemistry. To tackle both aspects, a multidisciplinary strategy has been exploited and a new, easily accessible synthetic approach to generate stable imine-intermediates in the gas phase and in solution has been introduced. The combination of this formation pathway, based on the thermal decomposition of hydrobenzamide, with a state-of-the-art computational characterization of phenylmethanimine laid the foundation for its first laboratory observation by means of rotational electric resonance spectroscopy. Both E and Z isomers have been accurately characterized, thus providing a reliable basis to guide future astronomical observations. A further characterization has been carried out by nuclear magnetic resonance spectroscopy, showing the feasibility of this synthetic approach in solution. The temperature dependence as well as possible mechanisms of the thermolysis process have been examined. 相似文献
8.
9.
A Dual Photoredox- and Cp2TiCl2-Catalyzed Approach for the Direct Access to α-Vinyl-β-hydroxy Esters
Emanuele Pinosa Prof. Andrea Gualandi Dr. Andrea Fermi Prof. Paola Ceroni Prof. Pier Giorgio Cozzi Dr. Francesco Calogero 《European journal of organic chemistry》2023,26(38):e202300421
For the first time, a dual photoredox- and titanocene-catalyzed methodology for the regioselective access to α-vinyl-β-hydroxy esters towards aldehyde allylation with 4-bromobut-2-enoate is reported. The protocol is based on the Barbier-type properties of the inexpensive and available Cp2TiCl2 in catalytic amount (5 mol%). The developed mild reaction conditions gave access to a library of differently functionalized α-vinyl-β-hydroxy esters in moderate diastereoselectivity, employing the commercially available ethyl 4-bromobut-2-enoate and both aromatic and aliphatic aldehydes. The reaction was realized under visible light irradiation, in the presence of an organophotocatalyst (3DPAFIPN, 2 mol%) combined with Hantzsch's ester as the sacrificial reductant. In contrast to other Barbier-type reactions employing ethyl 4-bromobut-2-enoate, the photoredox system ensures a better regioselectivity. Moreover, the use of preformed organometallic nucleophilic species (e. g., dienolborinates), and the need of metal reductants or stoichiometric amount of transition metals in low oxidation state for Barbier-type reactions, is avoided. To support the experimental evidence, a detailed photophysical study shed light on the mechanism of the reaction. 相似文献
10.
Dr. Elisa Brambilla Camilla Pozza Prof. Silvia Rizzato Prof. Giorgio Abbiati Dr. Valentina Pirovano 《European journal of organic chemistry》2023,26(3):e202201385
An enantioselective phosphine-catalyzed [3+2] cycloaddition between aza-aurones and allenoates is here described. The reaction proceeded under mild reaction conditions to afford 2-spirocyclopentyl indolin-3-one derivatives as single γ-isomer and with high levels of stereocontrol. 相似文献