全文获取类型
收费全文 | 1243篇 |
免费 | 91篇 |
国内免费 | 4篇 |
专业分类
化学 | 996篇 |
晶体学 | 3篇 |
力学 | 47篇 |
数学 | 134篇 |
物理学 | 158篇 |
出版年
2023年 | 10篇 |
2022年 | 21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 | 17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 | 6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1338条查询结果,搜索用时 15 毫秒
31.
Abdelhamid Elias M. Amine Didi Didier Villemin T. Semaoune S. Ouattas 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2599-2607
The reactions of phosphorus pentoxide with two alcohols and one phenol were performed in different conditions under microwave irradiation. The products (alkylphosphates and dialkylphosphates) were identical to those formed by classic heating and were obtained with better yields. The speed of the reaction was increased by a factor from 100 to 4000. 相似文献
32.
1,4-Diacetylpiperazine-2,5-dione (1) was condensated with aldehydes (2) with KF on alumina without solvent under microwaves or in at room temperature in the presence of DMF. The reaction was stereoselective and some natural products (4a-c) like albonursin(4c) were synthesized. 相似文献
33.
34.
Fouad Laoutid Marion Lorgouilloux Didier Lesueur Leila Bonnaud Philippe Dubois 《Polymer Degradation and Stability》2013
In this study, we evaluated the potential flame retardant effect of calcium-based hydrated minerals, such as hydrated lime, partially and completely hydrated dolomitic limes in polyethylene (MDPE) and ethylene vinyl acetate copolymers (EVA) and compared to that obtained with magnesium di-hydroxide (MDH). The most significant flame retardant effects, observed using the mass loss calorimeter test, indicated that Ca-based MDPE composites showed similar peak Heat Release Rate (pHRR) level to that obtained with MDH composite while the pHRR was lower for Ca-based fillers in EVA compositions. X-ray Diffraction (XRD) data, combined with thermal analysis results, indicated that the calcium di-hydroxide plays a role in the formation of an intumescent cohesive residue during the combustion. Indeed, Ca(OH)2 reacts with CO2 formed during the thermal degradation of the polymer to generate CaCO3 (calcium carbonate) that contributes to the enhancement of the mechanical resistance of the residue. 相似文献
35.
36.
Thermo‐ and pH‐sensitive triblock copolymers with tunable hydrophilic/hydrophobic properties 下载免费PDF全文
Christophe Pottier Gaëlle Morandi Virginie Dulong Zied Souguir Luc Picton Didier Le Cerf 《Journal of polymer science. Part A, Polymer chemistry》2015,53(22):2606-2616
Polymers consisting of poly(acrylic acid) (PAA) and statistical poly[(acrylic acid)‐co‐(tert‐butylacrylate)] (P(AA‐co‐tBA)), attached to both extremities of Jeffamine® (D series based on a poly(propylene oxide) (PPO) with one amine function at each end) using atom transfer radical polymerization (ATRP) are presented in this article. An original bifunctional amide‐based macroinitiator was first elaborated from Jeffamine®. tBA polymerization was subsequently initiated from this macroinitiator. This polymerization occurs in a well‐controlled manner leading to narrow molecular weights distribution. Amphiphilic copolymers were finally obtained after complete or partial hydrolysis of the PtBA blocks into PAA. The control of the partial hydrolysis of tBA units, conducted in a concentrated HCl/tetrahydrofuran mixture, is demonstrated. The properties of the triblock copolymers were preliminary investigated in aqueous solution by absorbance, DLS measurements and SEC/MALS/DV/DRI analysis as a function of temperature and pH modifications, providing evidences of thermo‐ and pH‐sensitive self‐assembly of the copolymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2606–2616 相似文献
37.
38.
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
39.
40.
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