全文获取类型
收费全文 | 374篇 |
免费 | 24篇 |
专业分类
化学 | 310篇 |
晶体学 | 2篇 |
力学 | 19篇 |
数学 | 26篇 |
物理学 | 41篇 |
出版年
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 7篇 |
2017年 | 3篇 |
2016年 | 14篇 |
2015年 | 18篇 |
2014年 | 16篇 |
2013年 | 27篇 |
2012年 | 21篇 |
2011年 | 33篇 |
2010年 | 21篇 |
2009年 | 17篇 |
2008年 | 23篇 |
2007年 | 28篇 |
2006年 | 19篇 |
2005年 | 24篇 |
2004年 | 24篇 |
2003年 | 16篇 |
2002年 | 12篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1998年 | 8篇 |
1997年 | 1篇 |
1995年 | 4篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1962年 | 1篇 |
1872年 | 2篇 |
排序方式: 共有398条查询结果,搜索用时 15 毫秒
51.
Sigwalt D Holler M Iehl J Nierengarten JF Nothisen M Morin E Remy JS 《Chemical communications (Cambridge, England)》2011,47(16):4640-4642
Polyplexes prepared from DNA and globular compact polycationic derivatives constructed around a fullerene hexakis-adduct core have shown remarkable gene delivery capabilities. 相似文献
52.
Favier I Castillo AB Godard C Castillón S Claver C Gómez M Teuma E 《Chemical communications (Cambridge, England)》2011,47(27):7869-7871
Chiral carbohydrate-based diphosphites were used for Pd-catalysed asymmetric allylic substitution (alkylation, amination, phosphination) in neat ionic liquids (ILs). Pyrrolidinium-based IL led to the best activities, allowing an efficient catalyst immobilization. In the allylic amination (TOF > 3100 h(-1)), the catalyst could be recycled nine times preserving both activity and enantioselectivity. 相似文献
53.
Malick Camara Nasser Gharbi Emmanuelle Cocco Cedric Guignard Marc Behr Daniele Evers Pierre Orlewski 《International Journal for Ion Mobility Spectrometry》2011,14(1):39-47
Rapid, hyphenated detection techniques involving a gas chromatograph (GC) coupled to a classical time-of-flight ion mobility
(IMS) spectrometer, or more recently, to a micro-machined, miniature differential ion mobility spectrometer (DMS) are quite
attractive for in-situ detection of many kinds of volatile organic compounds (VOCs) of concern and notably of natural contaminants appearing in
the headspaces of selected foodstuff. This work aims at a rapid detection, identification and quantification of geosmin in
the headspace of grape must and of wine. Samples of white and red wines have both been analyzed with a hyphenated GC/DMS and
by Solid Phase Micro-Extraction (SPME) coupled to GC/MS taken as a reference. The detection of geosmin at concentrations below
the human olfactory threshold of 50 ng/L has been demonstrated. 相似文献
54.
Emmanuelle Canet Didier Revel Rmy Forrat Claire Baldy-Porcher Michel de Lorgeril Laurent Sebbag Jean-Paul Vallee Dominique Didier Michel Amiel 《Magnetic resonance imaging》1993,11(8):1139-1145
Superparamagnetic iron oxide particles (SPIOs) are usually referred to as T2 MR contrast agents, reducing signal intensity (SI) on T2-weighted MR images (negative enhancement). This study reports the original use of SPIOs as T1-enhancing contrast agents, primarily assessed in vitro, and then applied to an in vivo investigation of a myocardial perfusion defect. Using a strongly T1-weighted subsecond MR sequence with SPIOs intravenous (IV) bolus injection, MR imaging of myocardial vascularization after reperfusion was performed, on a dog model of coronary occlusion followed by reperfusion. Immediately after the intravenous bolus injection of 20 μmol/kg of SPIOs, a positive signal intensity enhancement was observed respectively, in the right and left ventricular cavity and in the nonischemic left myocardium. Moreover, compared to normal myocardium, the remaining ischemic myocardial region (anterior wall of the left ventricle) appeared as a lower and delayed SI enhancing area (cold spot). Mean peak SIE in the nonischemic myocardium (posterior wall) was significantly higher than in the ischemic myocardium (anterior wall) (110 ± 23% vs. 74 ± 22%, Mann-Whitney test < 1%, n1 = 6, n2 − n1 = 0, U > 2). In conclusion, the T1 effect of SPIOs at low dose, during their first intravascular distribution, suggests their potential use as positive markers to investigate the regional myocardial blood flow and some perfusion defects such as the “no-reflow phenomenon”. 相似文献
55.
Blandine Destrez Gaud Pinel Emmanuelle Bichon Fabrice Monteau Ren Lafont Bruno Le Bizec 《Rapid communications in mass spectrometry : RCM》2008,22(24):4073-4080
Ecdysteroids, which are steroid hormones in invertebrates, but which are also present in plants, could potentially be used as anabolic agents in food‐producing animals. The control of ecdysteroid misuse in cattle relies on the development of an efficient method for their detection in biological matrices at trace levels (µg L−1). In order to propose an analytical procedure dedicated to the identification of excreted 20‐hydroxyecdysone (20E) in urine and faecal samples of breeding animals, a comparative study of the spectrometric behaviour of these compounds was carried out both by LC/(ESI‐)/HRMSn (hybrid linear ion trap – orbital trap) and by LC/(ESI+)/MS/MS (triple quadrupole). This study revealed the formation of a large number of product ions both in positive and negative ion mode, corresponding to losses of water molecules and specific cleavages on the side chain. The sample preparation consisted of sequential purification on two solid‐phase extraction cartridges (SPE octadecylsilyl and SPE silica). The detection limits were around 0.5 µg L−1 in the selected reaction monitoring (SRM) mode and recoveries above 60% were obtained. The method was successfully applied to the analysis of real samples collected from calves treated with 60 mg 20E over 4 days. Analysis of the samples allowed the investigation of the kinetics of elimination of 20E in calf urine and determination of the time‐frame for the control of potential abuse. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
56.
Marquette CA Degiuli A Imbert-Laurenceau E Mallet F Chaix C Mandrand B Blum LJ 《Analytical and bioanalytical chemistry》2005,381(5):1019-1024
Two diagnostic chemiluminescent biochips were developed for either the detection of p53 gene point mutation or the serological detection of anti-HIV-1 p24 capsid protein. Both biochips were composed of 24 microarrays of latex beads spots (4×4) (150 m in diameter, 800 m spacing) entrapped in a poly(dimethylsiloxane) elastomer (PDMS). The latex beads, bearing oligonucleotide sequences or capsid protein, were spotted with a conventional piezoelectric spotter and subsequently transferred at the PDMS interface. The electron microscopy observation of the biochips showed how homogeneous and well distributed the spots could be. Point mutation detection on the codon 273 of the p53 gene was performed on the basis of the melting temperature difference between the perfect match sequence and the one base pair mismatch sequence. The hybridisation of a 20-mer oligonucleotide form the codon 273 including a one base pair mutation in its sequence on a biochip arrayed with non-muted and the muted complementary sequences, enabled a clear discrimination at 56°C between muted and wild sequences. Moreover, the quantitative measurement of the amount of muted sequence in a sample was possible in the range 0.4–4 pmol. Serological measurement of anti-HIV-1 p24 capsid protein on the biochip, prepared with 1-m-diameter latex beads, enabled the detection of monoclonal antibodies in the range 1.55–775 ng mL–1. Such a range could be lowered to 0.775 ng mL–1 when using 50-nm-diameter beads, which generated a higher specific surface. The validation of the biochip for the detection of anti-HIV-1 capsid protein antibodies was performed in human sera from seropositive and seronegative patients. The positivity of the sera was easily discriminated at serum dilutions below 1:1,000. 相似文献
57.
Tomasz Maciej Stepniewski Arturo Mancini Richard gren Mariona Torrens-Fontanals Meriem Semache Michel Bouvier Kristoffer Sahlholm Billy Breton Jana Selent 《Chemical science》2021,12(33):10990
Brain functions rely on neurotransmitters that mediate communication between billions of neurons. Disruption of this communication can result in a plethora of psychiatric and neurological disorders. In this work, we combine molecular dynamics simulations, live-cell biosensor and electrophysiological assays to investigate the action of the neurotransmitter dopamine at the dopaminergic D2 receptor (D2R). The study of dopamine and closely related chemical probes reveals how neurotransmitter binding translates into the activation of distinct subsets of D2R effectors (i.e.: Gi2, GoB, Gz and β-arrestin 2). Ligand interactions with key residues in TM5 (S5.42) and TM6 (H6.55) in the D2R binding pocket yield a dopamine-like coupling signature, whereas exclusive TM5 interaction is typically linked to preferential G protein coupling (in particular GoB) over β-arrestin. Further experiments for serotonin receptors indicate that the reported molecular mechanism is shared by other monoaminergic neurotransmitter receptors. Ultimately, our study highlights how sequence variation in position 6.55 is used by nature to fine-tune β-arrestin recruitment and in turn receptor signaling and internalization of neurotransmitter receptors.Neurotransmitter contacts within the receptor binding site differentially contribute to the overall functional response: transmembrane helix (TM) 5 contacts promote G protein coupling whereas concerted TM5–TM6 contacts enhance β-arrestin recruitment. 相似文献
58.
Despite the importance of a complete characterization of dendritic patterns in castings, the availability of studies on the development of tertiary dendrite arms is scarce in the literature. In the present study, the tip cooling rate, local solidification time, primary and tertiary dendrite arm spacings have been determined in Pb–Sb alloys castings directionally solidified under unsteady-state heat flow conditions. The alloys compositions experimentally examined are widely used in the as-cast condition for the manufacture of positive and negative grids of lead-acid batteries. The initial growth of tertiary dendritic arms from the secondary branches was found to occur only for a Pb–3.5 wt% Sb alloy at cooling rates in the range 0.4–0.2?K/s, with no evidence of this spacing pattern for Pb–Sb alloys having lower solute content. Tertiary dendritic branches have been observed along the entire casting lengths for alloys of the Pb–Sb hypoeutectic range having compositions higher than 4.0 wt% Sb. It is shown that a power function experimental law with a characteristic ?0.55 exponent is able to characterize the tertiary spacing evolution with the solidification cooling rate for alloys compositions ≥4.0 wt% Sb. The only exception was the Pb–3.5 wt% Sb alloy for which λ 3 exhibited significant lower values when compared with the experimental values obtained for the other Pb–Sb alloys for a same solidification cooling rate. 相似文献
59.
Anca‐Elena Dascalu Alina Ghinet Muriel Billamboz Emmanuelle Lipka 《Electrophoresis》2019,40(15):1986-1991
CD‐CZE methods were developed for complete stereoisomeric separations of a series of six γ‐lactam analogues, of which some were neutral, or cationic depending on the background electrolyte nature. The tested cyclodextrin was the versatile sulfobutylether‐ β‐CD, used either in a phosphate buffer using capillaries dynamically coated with polyethylene oxide or in a borate buffer using uncoated capillaries. Long‐end and short‐end modes and concentration variations of chiral selectors allowed finding conditions of complete separation of four out of the six derivatives (i.e., 1 , 2 , 3, and 4 ) in short run times, confirming their broad range of applications. To separate the two last compounds, the highly sulfated‐ γ‐CD was examined as chiral selector in acidic phosphate conditions. The enantiomers of the γ‐lactam analogues 5 and 6 were baseline resolved with 5.5 and 4%, respectively as concentration in the buffer. 相似文献
60.