全文获取类型
收费全文 | 815篇 |
免费 | 37篇 |
国内免费 | 3篇 |
专业分类
化学 | 548篇 |
晶体学 | 8篇 |
力学 | 25篇 |
数学 | 123篇 |
物理学 | 151篇 |
出版年
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 13篇 |
2020年 | 25篇 |
2019年 | 14篇 |
2018年 | 8篇 |
2017年 | 12篇 |
2016年 | 24篇 |
2015年 | 23篇 |
2014年 | 23篇 |
2013年 | 34篇 |
2012年 | 62篇 |
2011年 | 63篇 |
2010年 | 46篇 |
2009年 | 21篇 |
2008年 | 63篇 |
2007年 | 49篇 |
2006年 | 42篇 |
2005年 | 40篇 |
2004年 | 28篇 |
2003年 | 23篇 |
2002年 | 20篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1982年 | 4篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1973年 | 3篇 |
1969年 | 3篇 |
1939年 | 3篇 |
排序方式: 共有855条查询结果,搜索用时 15 毫秒
91.
Wayland E. Noland Christopher L. Etienne Nicholas P. Lanzatella 《Journal of heterocyclic chemistry》2011,48(2):381-388
Vinylindoles and vinylpyrroles were prepared from their corresponding aldehydes or ketones using the Peterson olefination, or by use of the Nysted reagent, a commercially available gem‐dimetallic compound. The two methods provide efficient and convenient access to these useful heterocyclic 1,3‐diene systems. J. Heterocyclic Chem., (2011). 相似文献
92.
In our continuous search for alpha-glucosidase inhibitors from plants, four new depsidones named brevipsidones A-D (1-4) were isolated from stem bark of Garcinia brevipedicellata together with known damnacanthal, scopoletin and a mixture of stigmasterol and beta-sitosterol. Structural elucidations were made by spectroscopic analyses including 2D-NMR data. 相似文献
93.
The present work reports on the synthesis and evaluation of a crosslinkable thiolated gelatin derivative. The effect of varying two parameters including the pH of the reaction buffer and the thiolating agent applied (i.e. N-acetylhomocysteine thiolactone versus Traut’s reagent) on the obtained modification degree was studied in a first part. The gelatin derivatives synthesized starting from N-acetylhomocysteine thiolactone and Traut’s reagent were characterized in depth using size exclusion chromatography and UV–VIS spectrophotometry. In a subsequent part of the present work, hydrogel films were prepared starting from the thiolated gelatin derivative developed using N-acetylhomocysteine thiolactone. The contributions of both the chemical and the physical crosslinking of the hydrogels developed were studied in depth using rheology, swelling experiments and texturometry. The results indicate that the physical structuring, inherent to gelatin, contributes to a large extent to the mechanical properties. However, the chemical crosslinking mostly determines the final hydrogel properties and can be controlled to a large extent. The gelatin-based gels are flexible, strong and transparent. A major advantage of disulfide-crosslinked hydrogels is the fact that the crosslinking is reversible. The latter could be interesting in view of future applications as cell carriers for tissue engineering. 相似文献
94.
The cytochrome P450 (P450) enzymes are mainly localized to the endoplasmic reticulum (ER), where they function within catalytic
complexes metabolizing xenobiotics and some endogenous substrates. However, certain members of families 1–3 were also found
in other subcellular compartments, such as mitochondria, plasma membrane, and lysosomes. The physiological function of these
enzymes in non-ER locations is not known, although plasma-membrane-associated P450s have been described to be catalytically
active and to participate in immune-mediated reactions with autoantibody formation that can trigger drug-induced hepatitis.
Several retention/retrieval mechanisms are active in the ER retention of the P450s and inverse integration of the translated
P450 into the ER membrane appears to be responsible for transport to the plasma membrane. Furthermore, hydrophilic motifs
in the NH2-terminal part have been suggested to be important for mitochondrial import. Phosphorylation of P450s has been described to
be important for increased rate of degradation as well as for targeting into mitochondria. It was also suggested that the
mitochondria-targeted P450s from families 1–3 could be active in drug metabolism using an alternative electron transport chain.
In this review we present an update of the field emphasizing studies concerning localization, posttranslational modification,
such as phosphorylation, and intracellular transport of microsomal P450s. 相似文献
95.
Kesara Na-Bangchang Etienne Anagalou Guirou Anurak Cheomung Juntra Karbwang 《Chromatographia》2014,77(7-8):561-569
Primaquine (PQ) is the only 8-aminoquinoline antimalarial drug in clinical use because of its unique action on hypnozoites and gametocytes of Plasmodium species. We report here simple, sensitive and specific assay methods for the determination of PQ in human whole blood and dried blood spot (DBS) samples using high-performance liquid chromatography and liquid chromatography-mass spectrometry, respectively. Sample preparation was performed by a single or two-step liquid-liquid extraction with organic solvents. For whole blood analysis, separation was obtained on a reversed-phase C18 column with the mobile phase consisting of 0.25 % diethylamine and acetonitrile (7:3, v:v) running at a flow rate of 1.0 ml min?1. UV detection was at the wavelength 263 nm. For DBS analysis, separation was obtained on a reversed-phase column with the mobile phase consisting of methanol and 0.1 formic acid (1:3, v:v) running at a flow rate of 0.5 ml min?1. The selected ions generated by electrospray ionization were detected using mass spectrometer. Good precision and accuracy (both within-day and day-to-day assays) were obtained at the concentration ranges under investigation. Limits of quantification for PQ were accepted as 25 ng ml?1 using 500 μl whole blood and 5 ng ml?1 using 80 μl DBS samples. The mean recoveries for PQ and internal standard pyrimethamine (PYR) for both whole blood and DBS were over 70 %. The methods were successfully applied for a clinical pharmacology study of PQ in patients with Plasmodium vivax. Excellent correlation (r 2 = 0.997) was observed between the analysis of PQ in paired whole blood and DBS samples. 相似文献
96.
Isabelle Déléris Anne Saint‐Eve Etienne Sémon Hervé Guillemin Elisabeth Guichard Isabelle Souchon Jean‐Luc Le Quéré 《Journal of mass spectrometry : JMS》2013,48(5):594-607
For the on‐line monitoring of flavour compound release, atmospheric pressure chemical ionization (APCI) and proton transfer reaction (PTR) combined to mass spectrometry (MS) are the most often used ionization technologies. APCI‐MS was questioned for the quantification of volatiles in complex mixtures, but direct comparisons of APCI and PTR techniques applied on the same samples remain scarce. The aim of this work was to compare the potentialities of both techniques for the study of in vitro and in vivo flavour release. Aroma release from flavoured aqueous solutions (in vitro measurements in Teflon bags and glass vials) or flavoured candies (in vivo measurements on six panellists) was studied using APCI‐ and PTR‐MS. Very similar results were obtained with both techniques. Their sensitivities, expressed as limit of detection of 2,5‐dimethylpyrazine, were found equivalent at 12 ng/l air. Analyses of Teflon bag headspace revealed a poor repeatability and important ionization competitions with both APCI‐ and PTR‐MS, particularly between an ester and a secondary alcohol. These phenomena were attributed to dependency on moisture content, gas/liquid volume ratio, proton affinities and product ion distribution, together with inherent drawbacks of Teflon bags (adsorption, condensation of water and polar molecules). Concerning the analyses of vial headspace and in vivo analyses, similar results were obtained with both techniques, revealing no competition phenomena. This study highlighted the equivalent performances of APCI‐MS and PTR‐MS for in vitro and in vivo flavour release investigations and provided useful data on the problematic use of sample bags for headspace analyses. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
97.
Tandem CH Activation/Arylation Catalyzed by Low‐Valent Iron Complexes with Bisiminopyridine Ligands 下载免费PDF全文
Elise Salanouve Ghania Bouzemame Dr. Sébastien Blanchard Dr. Etienne Derat Dr. Marine Desage‐El Murr Prof. Louis Fensterbank 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4754-4761
Tandem C?H activation/arylation between unactivated arenes and aryl halides catalyzed by iron complexes that bear redox‐active non‐innocent bisiminopyridine ligands is reported. Similar reactions catalyzed by first‐row transition metals have been shown to involve substrate‐based aryl radicals, whereas our catalytic system likely involves ligand‐centered radicals. Preliminary mechanistic investigations based on spectroscopic and reactivity studies, in conjunction with DFT calculations, led us to propose that the reaction could proceed through an inner‐sphere C?H activation pathway, which is rarely observed in the case of iron complexes. This bielectronic noble‐metal‐like behavior could be sustained by the redox‐active non‐innocent bisiminopyridine ligands. 相似文献
98.
Xibo Yan Dr. Marco Delgado Dr. Amy Fu Pierre Alcouffe Dr. Sébastien G. Gouin Prof. Etienne Fleury Prof. Joseph L. Katz Dr. François Ganachaud Dr. Julien Bernard 《Angewandte Chemie (International ed. in English)》2014,53(27):6910-6913
A general, rapid, and undemanding method to generate at will functional oil‐filled nanocapsules through nanoprecipitation is reported. On the basis of polymer and hexadecane/water/acetone phase diagrams, the composition can be set so that polymer chains preferentially stick at the interface of the oil droplets to create nanocapsules. The nanocapsules can be decorated with biorelevant molecules (biotin, fluorescent tags, metal nanoparticles) within the shell and loaded with hydrophobic molecules in a simple one‐pot procedure. 相似文献
99.
A Highly Effective Ruthenium System for the Catalyzed Dehydrogenative Cyclization of Amine–Boranes to Cyclic Boranes under Mild Conditions 下载免费PDF全文
Dr. Christopher J. Wallis Dr. Gilles Alcaraz Dr. Alban S. Petit Dr. Amalia I. Poblador‐Bahamonde Dr. Eric Clot Dr. Christian Bijani Dr. Laure Vendier Dr. Sylviane Sabo‐Etienne 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(37):13080-13090
We recently disclosed a new ruthenium‐catalyzed dehydrogenative cyclization process (CDC) of diamine–monoboranes leading to cyclic diaminoboranes. In the present study, the CDC reaction has been successfully extended to a larger number of diamine–monoboranes ( 4 – 7 ) and to one amine–borane alcohol precursor ( 8 ). The corresponding NB(H)N‐ and NB(H)O‐containing cyclic diaminoboranes ( 12 – 15 ) and oxazaborolidine ( 16 ) were obtained in good to high yields. Multiple substitution patterns on the starting amine–borane substrates were evaluated and the reaction was also performed with chiral substrates. Efforts have been spent to understand the mechanism of the ruthenium CDC process. In addition to a computational approach, a strategy enabling the kinetic discrimination on successive events of the catalytic process leading to the formation of the NB(H)N linkage was performed on the six‐carbon chain diamine–monoborane 21 and completed with a 15N NMR study. The long‐life bis‐σ‐borane ruthenium intermediate 23 possessing a reactive NHMe ending was characterized in situ and proved to catalyze the dehydrogenative cyclization of 1 , ascertaining that bis σ‐borane ruthenium complexes are key intermediates in the CDC process. 相似文献
100.
M. Oubaha M. Dubois B. Murphy P. Etienne 《Journal of Sol-Gel Science and Technology》2006,38(2):111-119
A hybrid organic-inorganic material was prepared from the hydrolytic co-condensation of 3-trimethoxysilylpropylmethacrylate
(MAPTMS) and diphenyldiethoxysilane (DPHDES). The synthesis was performed in three steps: (1) MAPTMS pre-hydrolysis, (2) addition
of DPHDES, and (3) further hydrolysis of the obtained mixture. 29Si nuclear magnetic resonance spectroscopy was used to characterise the structural evolution of the mineral network during
the synthesis. It revealed the catalytic effect of DPHDES on the condensation reaction of silanol groups, initially observed
for pre-hydrolysed MAPTMS. In addition, it was clearly demonstrated that the formation of the highest condensed species of
the aromatic oligomers (D2 species) occurred only in the presence of aliphatic oligomers, which decrease the sterical hindrance about the silicon nuclei. 相似文献