全文获取类型
收费全文 | 1510篇 |
免费 | 45篇 |
国内免费 | 3篇 |
专业分类
化学 | 1066篇 |
晶体学 | 9篇 |
力学 | 29篇 |
数学 | 109篇 |
物理学 | 345篇 |
出版年
2023年 | 9篇 |
2022年 | 8篇 |
2021年 | 24篇 |
2020年 | 23篇 |
2019年 | 28篇 |
2018年 | 27篇 |
2017年 | 24篇 |
2016年 | 35篇 |
2015年 | 34篇 |
2014年 | 32篇 |
2013年 | 80篇 |
2012年 | 81篇 |
2011年 | 86篇 |
2010年 | 48篇 |
2009年 | 41篇 |
2008年 | 74篇 |
2007年 | 67篇 |
2006年 | 88篇 |
2005年 | 80篇 |
2004年 | 56篇 |
2003年 | 49篇 |
2002年 | 58篇 |
2001年 | 42篇 |
2000年 | 34篇 |
1999年 | 25篇 |
1998年 | 18篇 |
1997年 | 15篇 |
1996年 | 15篇 |
1995年 | 14篇 |
1994年 | 8篇 |
1993年 | 17篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 24篇 |
1989年 | 16篇 |
1988年 | 25篇 |
1987年 | 16篇 |
1986年 | 21篇 |
1985年 | 15篇 |
1984年 | 26篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 15篇 |
1975年 | 13篇 |
1974年 | 11篇 |
排序方式: 共有1558条查询结果,搜索用时 31 毫秒
31.
32.
33.
34.
Asymmetric monobenzoylation reactions of cyclic meso-1,3- and 1,4-diols were catalyzed by a phosphinite derivative of quinidine to afford the corresponding monobenzoylated diol with good yield and enantioselectivity. [reaction: see text] 相似文献
35.
36.
3-Epi-6,7-dideoxyxestobergsterol A (2), an analogue of xestobergsterol A, has been synthesized from dehydroepiandrosterone (3) in 15 steps. The key synthetic intermediate, 15beta,16alpha-dioxypregn-17(20)E-ene derivative 8, was prepared from the corresponding 15beta,16beta-epoxide 6 by treating with acetic acid and titanium tetraisopropoxide. The 23-oxo side chain was constructed stereoselectively by orthoester Claisen rearrangement of 8 followed by introduction of an isobutyl group. Basic treatment of the 15,23-diketone 12 followed by deprotection gave the title compound 2. 相似文献
37.
The objective was to examine how a bicontinuous cubic phase influences the diffusion and electrochemical activity of dissolved molecules. The cubic phase is a structure with three-dimensional continuous channels of water separated by an apolar membrane. A redox active molecule can dissolve in three different environments. A hydrophobic molecule will prefer the interior of the membrane, a hydrophilic molecule will prefer the water channels, and an amphiphilic molecule will be situated with its headgroup at the surface of the membrane and its tail in the interior. The electrochemical activity was measured with cyclic voltammetry and the transport behavior with chronocoulometry. All the molecules were redox active in the cubic phase; that is, all the molecules could reach the surface of the electrode and react. The cubic phase made the kinetics of the charge transfer slower, showing a quasi-reversible behavior. The reason may be that a layer of the membrane adheres to the hydrophobic electrode surface. The diffusion experiment showed that the diffusion was slower than in solution. The molecules that were restricted to diffuse within the membrane gave particularly low mass transport rates. 相似文献
38.
Marián Kucharík František Šimko Vladimír Danielik Miroslav Boča Roman Vasiljev 《Monatshefte für Chemie / Chemical Monthly》2007,138(12):1211-1215
Summary. The phase diagram of the system Na3AlF6–NaVO3 was determined by means of thermal analysis. The system is a simple binary eutectic one. The eutectic point was estimated
at x(NaVO3) = 0.975 and t
eut = 617°C. The XRD patterns of samples after thermal analysis revealed the presence of cryolite and NaVO3 only supporting the above assumption of a simple eutectic binary system. 相似文献
39.
Shinichi Yamabe Shigeki Kato Hiroshi Fujimoto Kenichi Fukui 《Theoretical chemistry accounts》1973,30(4):327-337
An ab initia molecular orbital calculation was done as to a reacting system, NH3+HF=NH4F, with the inclusion of the solvent effect as the origin of dipolar field. The reactants were assumed to stay in dimers, (NH3)2 and (HF)2, in advance to the reaction, and the respective partners of two reactants were regarded as point dipoles. The system was stabilized to some extent by two dipoles adopted. A study of configuration analysis on this system was made with and without the dipoles. Their effect was found to be favorable for proceeding of the reaction. 相似文献
40.
Jun Suzuki Kenjiro Fujimoto Toshiyuki Mori Mamoru Watanabe Yoshio Hasegawa 《Journal of Sol-Gel Science and Technology》2000,19(1-3):775-778
The photocatalytic reduction of nitrogen monoxide (NO) with ethane on the hollandite type catalyst (K2Ga2Sn6O16KGSO) was investigated. Using a closed-gas circulating system equipped with a Q-MASS detector and in-situ diffuse reflectance FT-IR spectroscopy. The reactant gases of NO and 13C2H6 decreased with the increasing irradiation time. In contrast, the N2 yield increased proportionally to the conversion of 13C2H6. Nitrogen oxides such as N2O did not reach their detectable levels. The NO adsorbed on KGSO was found to change to its activated species by UV irradiation. The oxidized products of C2H6 such as CH3CHO increased in proportion to the reaction time. The present results strongly suggest that KGSO has remarkable photocatalytic activity for the reduction of NO with C2H6. 相似文献