全文获取类型
收费全文 | 1230篇 |
免费 | 91篇 |
国内免费 | 4篇 |
专业分类
化学 | 984篇 |
晶体学 | 3篇 |
力学 | 47篇 |
数学 | 134篇 |
物理学 | 157篇 |
出版年
2023年 | 10篇 |
2022年 | 10篇 |
2021年 | 29篇 |
2020年 | 32篇 |
2019年 | 26篇 |
2018年 | 29篇 |
2017年 | 21篇 |
2016年 | 42篇 |
2015年 | 54篇 |
2014年 | 45篇 |
2013年 | 82篇 |
2012年 | 78篇 |
2011年 | 94篇 |
2010年 | 60篇 |
2009年 | 56篇 |
2008年 | 91篇 |
2007年 | 83篇 |
2006年 | 74篇 |
2005年 | 53篇 |
2004年 | 61篇 |
2003年 | 56篇 |
2002年 | 45篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 11篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有1325条查询结果,搜索用时 31 毫秒
51.
52.
Cyclohexanone and morpholine in the presence of KSF under azeotropic distillation gave 1-morpholinocyclohexene which is alkylated or acylated in situ without isolation of the enamine. The overall yield of these Stork's reactions are better or equivalent to those obtained by isolation of the enamine. 相似文献
53.
54.
Tabbi Hanane Amel Bendjeddou Didier Villemin 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):697-704
AbstractThe synthesis of the title compounds has been carried out by condensation via a Wittig-type reaction of a pyridinium hexafluorophosphate with a phosphonate ester to give the desired (4-nitrophenyl)tetrathiafulvalene the nitro group of which was reduced to an amino group. Reaction of the amine with chlorosulfonyl isocyanate and subsequently with tert-butyl alcohol gave the corresponding open-chain sulfamide. Cyclization under basic conditions and de-protection led to 2-[4-(4′,5′-dipropyltetrathiafulvalen-4-yl)]phenyl-1,2,6-thiadiazinane 1,1-dioxide. Finally, N-alkylated and N-acylated cyclic sulfamides linked to tetrathiafulvalene were obtained. Their electron donor ability was measured by cyclic voltammetry. A detailed DFT study based on B3LYP/6–31G (d,p) of electronic properties is also presented. The calculated molecular electrostatic potential shows that, the negative charge covers the nitro and sulfamide function, while positive charge is located at the hydrogen atoms of the amine and sulfamide rings. The calculated HOMO and LUMO energy reveals that charge transfer occurs within the molecule. The chemical reactivity parameters reveal that tetrathiafulvalene 1 is highly reactive, which facilitates the desired formation of the cyclic sulfamide. The first hyperpolarizability βtot shows that compounds 1 and 5 are good candidates as a NLO material. 相似文献
55.
The synthesis of 3-methyl-7-[2-(dimethylaminoethyl)oximino]-5-arylcyclopenta [f] benzoxa-zolinones, potential ligands of the 5HT1D receptors is described through a 4 steps reaction strategy from 3-methyl-6-acetyl benzoxazolinone. 相似文献
56.
Fatiha Zaoui Mohamed Amine Didi Didier Villemin 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(1):419-424
A new 8-hydroxyquinoline derivative extractant was synthesized via the Mannich reaction from a secondary amine. Various analytical techniques (1H, 13C NMR, FTIR, mass spectroscopy) were used to characterize our product. The use of this new extractant for the uptake and removal of uranyl ions in aqueous solution was investigated. Conditions for an effective sorption were optimized with respect to different experimental parameters in batch process. The results showed that the extraction rate increases for solutions with a pH in the range [0.65–1.13]. The total sorption capacity was 105 (mg g?1) under optimum experimental conditions. The extraction of UO2 2+ was found to be quantitative (100 %) at initial uranyl concentration less than or equal to 41.59 mg/L. Thermodynamic parameters showed the adsorption of an endothermic process and a spontaneous nature, respectively. 相似文献
57.
Dr. Matthieu Fonvielle Dénia Mellal Delphine Patin Maxime Lecerf Dr. Didier Blanot Dr. Ahmed Bouhss Dr. Marco Santarem Dr. Dominique Mengin‐Lecreulx Dr. Matthieu Sollogoub Dr. Michel Arthur Dr. Mélanie Ethève‐Quelquejeu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(4):1357-1363
Peptidyl–RNA conjugates have various applications in studying the ribosome and enzymes participating in tRNA‐dependent pathways such as Fem transferases in peptidoglycan synthesis. Herein a convergent synthesis of peptidyl–RNAs based on Huisgen–Sharpless cycloaddition for the final ligation step is developed. Azides and alkynes are introduced into tRNA and UDP‐MurNAc‐pentapeptide, respectively. Synthesis of 2′‐azido RNA helix starts from 2′‐azido‐2′‐deoxyadenosine that is coupled to deoxycytidine by phosphoramidite chemistry. The resulting dinucleotide is deprotected and ligated to a 22‐nt RNA helix mimicking the acceptor arm of Ala‐tRNAAla by T4 RNA ligase. For alkyne UDP‐MurNAc‐pentapeptide, meso‐cystine is enzymatically incorporated into the peptidoglycan precursor and reduced, and L ‐Cys is converted to dehydroalanine with O‐(mesitylenesulfonyl)hydroxylamine. Reaction of but‐3‐yne‐1‐thiol with dehydroalanine affords the alkyne‐containing UDP‐MurNAc‐pentapeptide. The CuI‐catalyzed azide alkyne cycloaddition reaction in the presence of tris[(1‐hydroxypropyl‐1H‐1,2,3‐triazol‐4‐yl)methyl]amine provided the peptidyl‐RNA conjugate, which was tested as an inhibitor of non‐ribosomal FemXWv aminoacyl transferase. The bi‐substrate analogue was found to inhibit FemXWv with an IC50 of (89±9) pM , as both moieties of the peptidyl–RNA conjugate contribute to high‐affinity binding. 相似文献
58.
Dr. Alberto Lena Dr. Alessandra Benassi Michele Stasi Christine Saint-Pierre Prof. Mauro Freccero Dr. Didier Gasparutto Dr. Sophie Bombard Prof. Filippo Doria Dr. Daniela Verga 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(35):e202200734
Combining the selectivity of G-quadruplex (G4) ligands with the spatial and temporal control of photochemistry is an emerging strategy to elucidate the biological relevance of these structures. In this work, we developed six novel V-shaped G4 ligands that can, upon irradiation, form stable covalent adducts with G4 structures via the reactive intermediate, quinone methide (QM). We thoroughly investigated the photochemical properties of the ligands and their ability to generate QMs. Subsequently, we analyzed their specificity for various topologies of G4 and discovered a preferential binding towards the human telomeric sequence. Finally, we tested the ligand ability to act as photochemical alkylating agents, identifying the covalent adducts with G4 structures. This work introduces a novel molecular tool in the chemical biology toolkit for G4s. 相似文献
59.
The doped two-dimensional quantum dimer model is investigated by numerical techniques on the square and triangular lattices, with significantly different results. On the square lattice, at small enough doping, there is always a phase separation between an insulating valence-bond solid and a uniform superfluid phase, whereas on the triangular lattice, doping leads directly to a uniform superfluid in a large portion of the resonating-valence-bond (RVB) phase. Under an applied Aharonov-Bohm flux, the superfluid exhibits quantization in terms of half-flux quanta, consistent with Q=2e elementary charge quanta in transport properties. 相似文献
60.
Maximilian Joost Dr. Pauline Gualco Dr. Yannick Coppel Dr. Karinne Miqueu Dr. Christos E. Kefalidis Dr. Laurent Maron Dr. Abderrahmane Amgoune Dr. Didier Bourissou 《Angewandte Chemie (International ed. in English)》2014,53(3):747-751
Oxidative addition plays a major role in transition‐metal catalysis, but this elementary step remains very elusive in gold chemistry. It is now revealed that in the presence of GaCl3, phosphine gold chlorides promote the oxidative addition of disilanes at low temperature. The ensuing bis(silyl) gold(III) complexes were characterized by quantitative 31P and 29Si NMR spectroscopy. Their structures (distorted Y shape) and the reaction profile of σ(Si? Si) bond activation were analyzed by DFT calculations. These results provide evidence for the intermolecular oxidative addition of σ(Si? Si) bonds to gold and open promising perspectives for the development of new gold‐catalyzed redox transformations. 相似文献