全文获取类型
收费全文 | 1058篇 |
免费 | 39篇 |
国内免费 | 3篇 |
专业分类
化学 | 755篇 |
晶体学 | 6篇 |
力学 | 33篇 |
数学 | 174篇 |
物理学 | 132篇 |
出版年
2024年 | 5篇 |
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 19篇 |
2020年 | 18篇 |
2019年 | 20篇 |
2018年 | 16篇 |
2017年 | 14篇 |
2016年 | 31篇 |
2015年 | 22篇 |
2014年 | 38篇 |
2013年 | 48篇 |
2012年 | 87篇 |
2011年 | 116篇 |
2010年 | 74篇 |
2009年 | 53篇 |
2008年 | 83篇 |
2007年 | 55篇 |
2006年 | 69篇 |
2005年 | 51篇 |
2004年 | 51篇 |
2003年 | 48篇 |
2002年 | 41篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 14篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 5篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1100条查询结果,搜索用时 15 毫秒
991.
992.
R. Razafindrabe Christian Aubry Sylvain Bourdon Benjamin Andriantsiferana Marta Pellet-Rostaing Stephane Lemaire Marc 《中国科学:化学(英文版)》2010,53(9):1888-1898
A synthesis of functionalized phenolic α-amino-alcohols (±)-8 and (±)-16 as synthetic precursors of the catechol tetrahydroisoquinoline structure of phthalascidin 650 was disclosed. (±)-8 was prepared in 5 steps from the commercially available sesamol. Starting from 3-methyl catechol 5, 8 steps gave rise to the synthesis of phenolic α-amino-alcohol (±)-16 in 27% overall yield. This synthetic strategy involved the elaboration of fully functionalized aromatic aldehyde 13 and its transformation into a phenolic α-amino-alcohol (±)-16, through a Knoevenagel condensation, simultaneous reduction of nitroketene and ester functions, and hydrogenolysis of the benzyl protecting group. The pentacycle (±)-4 was obtained after 4 additional steps. The Pictet-Spengler cyclisation between the phenolic α-amino-alcohol (±)-16 and the N-protected α-amino-aldehyde 4 allowed to obtain (1,3′)-bis-tetrahydroisoquinoline 17 with N-methylated and N-Fmoc removed. The last step was a Swern oxidation allowing the expected intramolecular condensation. 相似文献
993.
Protein adsorption onto capillary wall often hampers CE separations, particularly in the CZE mode. Electrostatic interactions are not the only factors affecting adsorption, as hydrophobic interactions and/or protein conformational changes are also involved in the adsorption phenomenon. Numerous methods can be used to reduce or avoid adsorption, such as (i) addition of low molecular weight molecules in the BGE, (ii) use of surfactants, or (iii) capillary coatings. However, most of these methods are not MS-compatible. In this study, we evaluated the addition of organic solvent as an alternative MS-compatible method to decrease protein adsorption. The effect of the solvent addition was emphasized using classical methods for estimating reversible and irreversible adsorption. In many cases, organic solvents were effective at decreasing adsorption. However, the influence of the organic solvent on protein adsorption should be evaluated case-by-case in CE method development. 相似文献
994.
Sylvain Brochard 《Mathematische Annalen》2009,343(3):541-602
995.
Guillermo Orts Gil Sylvain Prévost Magdalena Łosik Florian Hermes Helmut Schlaad Thomas Hellweg 《Colloid and polymer science》2009,287(11):1295-1304
The self-assembly of polystyrene-block-poly(l-lysine) (PS-PLLys·HCl) copolymers with different block lengths has been studied in toluene. The obtained spherical micelles exhibit size variations upon addition of acids or bases, as indicated by light and neutron scattering studies. It is shown that pyridine induces a shrinking of the polystyrene chains in the corona region of the micelles, decreasing the aggregate solvent interface. The addition of benzoic acid, on the other hand, leads to a swelling of the copolymer micelles proportional to the molar fraction of polypeptide. This behavior suggests a selective permeability of the PS-PLLys micelles and the possibility to encapsulate organic compounds in toluene depending on their chemical nature. 相似文献
996.
Jos Alberto Galicia Aguilar Sylvain Berns 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(4):o176-o178
3,6‐Dinitrodurene (1,2,4,5‐tetramethyl‐3,6‐dinitrobenzene), C10H12N2O4, has been crystallized in two polymorphic forms which may be distinguished by their colours in the solid state. Polymorph I gives clear colourless prismatic crystals, while polymorph II crystallizes in the dark and under an inert atmosphere as irregular purple blocks. Both forms belong to the space group C2/c, with both asymmetric units containing two half‐molecules. One molecule is located on an inversion centre and the other lies on a twofold axis. The polymorphism arises from different orientations of the twofold axis: in form I, this axis passes through the mid‐points of two C—C bonds of the benzene ring and, as a consequence, all atoms in the asymmetric unit are in general positions. In form II, the N atoms of the nitro groups and the Cipso atoms are located on the binary axis. Comparing phases I and II, slightly different conformations are observed for the nitro substituents, while the stacking structures are very similar. 相似文献
997.
Hana Ben Abderrazak Aurélie Fildier Sylvain Marque Damien Prim Hatem Ben Romdhane Hans R. Kricheldorf Saber Chatti 《European Polymer Journal》2011,(11):2097-2110
New polyesters were prepared by polycondensation in solution of 1,4:3,6 dianhydrohexitols with various aliphatic–aromatic acid dichlorides which differ by their chain length (m = 6,8,10). They are obtained with yields in the range of between 89% and 95%. In order to obtain these polymers within optimum conditions, a systematic study was conducted on the effect of the parameters involved in the reaction, such as the alkyl chain length of acid dichlorides and the endo or exo positions of hydroxyl function of diols. The resulting polyesters were characterized by different analytical techniques such as NMR (1H and 13C), FT-IR spectrometry, SEC measurements and MALDI-ToF mass spectrometry. Under optimized conditions a high molar fraction of cyclic polyesters was formed.The differential scanning calorimetry (DSC) measurements revealed an amorphous character with glass transition temperatures in the range of 27–45 °C. The polymers are obtained with inherent viscosities in the range of 0.11–0.25 dL/g with a polydispersity index between 1.75 and 1.99. 相似文献
998.
Agullo J Canesi S Schaper F Morin M Bélanger D 《Langmuir : the ACS journal of surfaces and colloids》2012,28(10):4889-4895
The in situ generation of 3-diazonium cations from 3-aminopyridine and their subsequent stability under experimental conditions used for electrografting of pyridine groups were investigated by spectroscopy and electrochemistry. UV spectroscopy revealed the rapid kinetics for the reaction of 3-aminopyridine with sodium nitrite in HCl to form the 3-diazopyridinium cation with a second-order rate constant of 550 ± 20 L mol(-1) s(-1) at 22 °C. UV spectroscopy showed that the 3-diazopyridinium ion was relatively unstable and its transformation into 3-hydroxypyridine was proven by (1)H NMR. Its hydrolytic decomposition was investigated by NMR and followed first-order kinetics with a rate constant of (53 ± 5) × 10(-3) s(-1) at 22 °C. These results enable us to establish the appropriate conditions for the electrografting of pyridine from the corresponding diazonium cations generated in situ. The electrochemical modification of glassy carbon electrodes with pyridine was characterized by cyclic voltammetry and the resulting grafted layer by electrochemical impedance spectroscopy in the presence of Fe(CN)(6)(3-/4-) as redox probes. The effect of diazotization time before electrochemical reduction on the blocking effect of the grafted layer was investigated and showed that an increase of the diazotization time led to less efficient grafting. The presence of immobilized pyridine on the electrode surface was demonstrated by X-ray photoelectron spectroscopy measurements, and a surface coverage of 8.8 × 10(-10) mol cm(-2) was estimated for the grafted pyridine groups. The significance of these results for researchers using the in situ generation approach for electrochemical and chemical grafting is discussed. 相似文献
999.
Zhu Y Smith DA Herbert DE Gatard S Ozerov OV 《Chemical communications (Cambridge, England)》2012,48(2):218-220
Reactions of a series of phenyl esters with a (PNP)Rh fragment have been studied. PhO(2)CPh only underwent C-H oxidative addition (OA). PhO(2)CCF(3) chiefly underwent acyl-oxygen OA. PhO(2)CBu(t) and PhO(2)CNEt(2) initially underwent OA of an ortho-C-H bond of the phenyl group but continued thermolysis led to the phenyl-oxygen OA products. 相似文献
1000.
Ledreux A Sérandour AL Morin B Derick S Lanceleur R Hamlaoui S Furger C Biré R Krys S Fessard V Troussellier M Bernard C 《Analytical and bioanalytical chemistry》2012,403(7):1995-2007
Successive unexplained shellfish toxicity events have been observed in Arcachon Bay (Atlantic coast, France) since 2005. The positive mouse bioassay (MBA) revealing atypical toxicity did not match the phytoplankton observations or the liquid chromatography-tandem mass spectrometry (LC-MS/MS) investigations used to detect some known lipophilic toxins in shellfish. The use of the three cell lines (Caco2, HepG2, and Neuro2a) allows detection of azaspiracid-1 (AZA1), okadaic acid (OA), or pectenotoxin-2 (PTX2). In this study, we proposed the cell-based assays (CBA) as complementary tools for collecting toxicity data about atypical positive MBA shellfish extracts and tracking their chromatographic fractionation in order to identify toxic compound(s). The present study was intended to investigate the responses of these cell lines to shellfish extracts, which were either control or spiked with AZA1, OA, or PTX2 used as positive controls. Digestive glands of control shellfish were extracted using the procedure of the standard MBA for lipophilic toxins and then tested for their cytotoxic effects in CBA. The same screening strategy previously used with pure lipophilic toxins was conducted for determining the intra- and inter-laboratory variabilities of the responses. Cytotoxicity was induced by control shellfish extracts whatever the cell line used and regardless of the geographical origin of the extracts. Even though the control shellfish extracts demonstrated some toxic effects on the selected cell lines, the extracts spiked with the selected lipophilic toxins were significantly more toxic than the control ones. This study is a crucial step for supporting that cell-based assays can contribute to the detection of the toxic compound(s) responsible for the atypical toxicity observed in Arcachon Bay, and which could also occur at other coastal areas. 相似文献