全文获取类型
收费全文 | 184篇 |
免费 | 6篇 |
专业分类
化学 | 156篇 |
力学 | 2篇 |
数学 | 10篇 |
物理学 | 22篇 |
出版年
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 13篇 |
2012年 | 17篇 |
2011年 | 12篇 |
2010年 | 8篇 |
2009年 | 9篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2000年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1968年 | 1篇 |
1963年 | 3篇 |
1957年 | 1篇 |
1954年 | 1篇 |
1952年 | 1篇 |
1949年 | 1篇 |
1948年 | 2篇 |
1947年 | 7篇 |
1940年 | 1篇 |
1938年 | 2篇 |
排序方式: 共有190条查询结果,搜索用时 46 毫秒
121.
Alajarín M Cabrera J Pastor A Sánchez-Andrada P Bautista D 《The Journal of organic chemistry》2007,72(6):2097-2105
Somewhat unexpectedly, the computed highest occupied molecular orbital (HOMO) energies of some 4-alkenylthiazoles afforded values close to those calculated for the Danishefsky-Kitahara and Rawal dienes. In fact, 4-alkenylthiazoles behave as all-carbon dienes in Diels-Alder reactions with the participation of the formal C-C double bond of the thiazole ring and the side-chain double bond. The reactions with N-substituted maleimides, maleic anhydride, and naphthoquinone take place with high levels of stereocontrol to give the corresponding endo-cycloadducts in good to excellent yields. Depending on the dienophile, the cycloadduct further transforms under the reaction conditions through either a 1,3-hydrogen shift, dehydrogenation, or an ene reaction or Michael addition with another molecule of dienophile. These unprecedented results open new synthetic perspectives for the functionalization of the thiazole ring. 相似文献
122.
Simple DPPH.‐Based Electrochemical Assay for the Evaluation of the Antioxidant Capacity: a Thorough Comparison with Spectrophotometric Assays and Evaluation with Real‐World Samples 下载免费PDF全文
Veronica Andrei Ada‐Ioana Bunea Aurelia Tudorache Szilveszter Gáspár Alina Vasilescu 《Electroanalysis》2014,26(12):2677-2685
An assay based on the electrochemical detection of 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH.) for the evaluation of the total antioxidant capacity (TAC) was optimized. The assay is interchangeable with the classic spectrophotometric tests for TAC based on the same radical. In addition, it can be used for the analysis of dilute samples with low antioxidant capacities. A good linear correlation (R2=0.97) was obtained between the results obtained with the proposed electrochemical assay and the Trolox Equivalent Antioxidant Capacity test based on ABTS radical. The assay was successfully used to evaluate the antioxidant capacity of two red wines obtained by six different maceration‐fermentation techniques. 相似文献
123.
The pincer complex [Pd(C1,O1,N1-L)(NCMe)]ClO4 (L = monoanionic ligand resulting from deprotonation of the acetyl group of the dimethyl monoketal of 2,6-diacetylpyridine) is used for the high-yield and selective catalytic hydrolysis of aliphatic, aromatic, cyclic, and acyclic dimethyl-acetals, -ketals, and dioxolanes, even in the presence of large substituents. Other protecting groups, such as THP or TBDMS, or very acid-sensitive alcohols were not affected. The catalyst is easily prepared in high yield from Pd(AcO)2 and 2,6-diacetylpyridinium perchlorate stable to air and moisture, easily and fully recoverable and reusable. 相似文献
124.
Helene Pezous Carole Rossi Marjorie Sanchez Fabrice Mathieu Xavier Dollat Samuel Charlot Véronique Conédéra 《Journal of Physics and Chemistry of Solids》2010,71(2):75-79
We propose a safe, arm and fire (SAF) device that could constitute a real breakthrough for safe miniature fuzing device. It integrates all the functions of a conventional mechanical arm and fire system and integrates them within 1 cm3. For the first time, it combines a mechanical arming unit with electrical safety functionalities on the same silicon initiator's chip. It requires only 635 mW for ignition. 相似文献
125.
126.
127.
128.
I. Simiti H. Demian Aurelia Marie N. Palibroda N. Palibroda 《Journal of mass spectrometry : JMS》1980,15(4):172-174
The fragmentation patterns of thiazolotriazoles are in agreement with the individual character of each heterocycle but there are also peaks arising both from their combined influence and from the nature of the substituents in positions 5 and 6. 相似文献
129.
Alajarin M Orenes RA Howard JA Spencer EC Steed JW Pastor A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(8):2389-2397
Tris(2- and 3-ureidobenzyl)amines with C(s) symmetry self-assemble in solution forming mixtures of regioisomeric capsular aggregates, one of which is chiral and the other centrosymmetric. Under certain conditions, a predominance of the centrosymmetric regioisomer is found before equilibrium, that is, a mixture close to the statistical ratio of the two species is reached. In the solid state, there is a preference for the centrosymmetric capsules. Molecular models of both regioisomeric aggregates have been built and analyzed for comparison. Guests inside capsules formed by self-assembly of desymmetrized tris(3-ureidobenzyl)amines feel different magnetic environments, depending on whether they are inside a chiral or an achiral regioisomeric container. Of special significance are the experiments with a more flexible triurea endowed with an ureidopropylic arm, which self-assembles with the same efficiency as the more rigid tris(ureidobenzyl)amines. 相似文献
130.
Juliá-Hernández F Arcas A Vicente J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(25):7780-7786
The complex [Pd(O,N,C-L)(OAc)], in which L is a monoanionic pincer ligand derived from 2,6-diacetylpyridine, reacts with 2-iodobenzoic acid at room temperature to afford the very stable pair of Pd(IV) complexes (OC-6-54)- and (OC-6-26)-[Pd(O,N,C-L)(O,C-C(6)H(4)CO(2)-2)I] (1.5:1 molar ratio, at -55?°C). These complexes and the Pd(II) species [Pd(O,N,C-L)(OX)] and [Pd(O,N,C-L')(NCMe)]ClO(4), (X = MeC(O) or ClO(3), L' = another monoanionic pincer ligand derived from 2,6-diacetylpyridine), are precatalysts for the arylation of CH(2)=CHR (R = CO(2)Me, CO(2)Et, Ph) using IC(6)H(4)CO(2)H-2 and AgClO(4). These catalytic reactions have been studied and a tentative mechanism is proposed. The presence of two Pd(IV) complexes was detected by ESI(+)-MS during the catalytic process. All the data obtained strongly support a Pd(II)/Pd(IV) catalytic cycle. 相似文献