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191.
A stepwise approach to the formation of heterometallic discrete complexes and infinite architectures
Baudron SA Hosseini MW Kyritsakas N Kurmoo M 《Dalton transactions (Cambridge, England : 2003)》2007,(11):1129-1139
A strategy for the controlled construction of heterobimetallic discrete complexes and 1-D coordination networks is presented. The organic ligand based on the methanedithiolate group and the 4,5-diazafluorene moiety behaving as primary and secondary coordination poles respectively leads to the formation of a series of discrete metal complexes with various geometries via binding through the dithiolate site. The observed coordination geometries range from square-planar for Ni(ii) and Pd(ii) to distorted tetrahedral for Zn(ii) and Hg(ii). The square-planar Pd(ii) complex affords a discrete bimetallic trinuclear complex when treated with a capped Ni(ii) center. All three Ni(ii), Pd(ii) and Hg(ii) discrete complexes have been also shown to behave as metallatectons leading to the generation of infinite networks in the presence of bridging cations such as sodium. 相似文献
192.
Perla Hajjar Marie-Agns Lacour Nathalie Masquelez Julien Cambedouzou Sophie Tingry David Cornu Yaovi Holade 《Molecules (Basel, Switzerland)》2021,26(19)
Given the limited access to freshwater compared to seawater, a growing interest surrounds the direct seawater electrolysis to produce hydrogen. However, we currently lack efficient electrocatalysts to selectively perform the oxygen evolution reaction (OER) over the oxidation of the chloride ions that are the main components of seawater. In this contribution, we report an engineering strategy to synthesize heterogeneous electrocatalysts by the simultaneous formation of separate chalcogenides of nickel (NiSx, x = 0, 2/3, 8/9, and 4/3) and cobalt (CoSx, x = 0 and 8/9) onto a carbon-nitrogen-sulfur nanostructured network. Specifically, the oxidative aniline polymerization in the presence of metallic cations was combined with the calcination to regulate the separate formation of various self-supported phases in order to target the multifunctional applicability as both hydrogen evolution reaction (HER) and OER in a simulated alkaline seawater. The OER’s metric current densities of 10 and 100 mA cm−2 were achieved at the bimetallic for only 1.60 and 1.63 VRHE, respectively. This high-performance was maintained in the electrolysis with a starting voltage of 1.6 V and satisfactory stability at 100 mA over 17 h. Our findings validate a high selectivity for OER of ~100%, which outperforms the previously reported data of 87–95%. 相似文献
193.
We study the almost sure asymptotic behaviors of the Lebesgue measure of the points which are hardly visited, in the sense of Földes and Révész,(7) by a linear Wiener process. 相似文献
194.
Bertrand Alluis Nathalie Prol Hakima Elhajji Olivier Dangles 《Helvetica chimica acta》2000,83(2):428-443
Water‐soluble derivatives of rutin, a very common glycoside of quercetin (=3,3′,4′,5,7‐pentahydroxyflavone=2‐(3,4‐dihydroxyphenyl)‐3,5,7‐trihydroxy‐4H‐1‐benzopyran‐4‐one) and a potent plant antioxidant from the flavonol family, were synthesized by simple chemical procedures aimed at introducing carboxy or sulfo groups at the sugar moiety (Scheme 1). Such derivatives form stable molecular complexes with malvin, a polyphenolic pigment from the anthocyanin family, and thereby prove to be very effective in the enhancement (hyperchromism) and variation (bathochromism) of natural colours. The H2O‐solubilizing carboxylate and sulfate groups are shown to deeply modify the enthalpy‐entropy balance of the pigment‐flavonol complexation (copigmentation). A molecular interpretation of the complexation‐induced bathochromic shift in the pigment VIS band is proposed. Finally, the H2O‐soluble rutin derivatives are shown to retain the high antioxidant ability of rutin as evidenced by their efficient trapping of the coloured radical DPPH (=2,2‐diphenyl‐1‐(2,4,6‐trinitrophenyl)hydrazyl). 相似文献
195.
Sophie Laurent Luce VanderElst Sylvain Houz Nathalie Gurit RobertN. Muller 《Helvetica chimica acta》2000,83(2):394-406
Four derivatives of diethylenetriaminepentaacetic acid (=3,6,9‐tris(carboxymethyl)‐3,6,9‐triazaundecanedioic acid (H5dtpa)), potential contrast agents for magnetic resonance imaging (MRI), carrying benzyl groups at various positions of the parent structure were synthesized and characterized by a thorough multinuclear NMR study, i.e., the (S)‐ and (R)‐stereoisomers 1a and 1b of 4‐benzyl‐3,6,9‐tris(carboxymethyl)‐3,6,9‐triazaundecanedioic acid (H5[(S)‐(4‐Bz)dtpa] and H5[(R)‐(4‐Bz)dtpa], the diamide derivative N,N″‐bis[(benzylcarbamoyl)methyl]diethylenetriamine‐N,N′,N″‐triacetic acid (=3,9‐bis[2‐(benzylamino)‐2‐oxoethyl]‐6‐(carboxymethyl)‐3,6,9‐triazaundecanedioic acid; H3[dtpa(BzA)2]; 2 ), and the diester derivative N,N″‐bis{[(benzyloxy)carbonyl]methyl}diethylenetriamine‐N,N′,N″‐triacetic acid (=3,9‐bis[2‐(benzyloxy)‐2‐oxoethyl]‐6‐(carboxymethyl)‐3,6,9‐triazaundecanedioic acid; H3[dtpa(BzE)2]; 3 ). From the 17O‐NMR chemical shift of H2O induced by their dysprosium complexes with ligands 1 – 3 , it was concluded that only one H2O molecule is contained in the first coordination sphere of these lanthanide complexes. The rotational correlation times (τR) of the complexes were estimated from the 2H‐NMR longitudinal relaxation rate of the deuterated diamagnetic lanthanum complexes. The exchange time of the coordinated H2O molecule (τM) was studied through the temperature dependence of the 17O‐NMR transverse relaxation rate. As compared to [Gd(dtpa)]2−, the H2O‐exchange rate is faster for [Gd{(S)‐(4‐Bz)dtpa}]2− and [Gd{(R)‐(4‐Bz)dtpa}]2−‐, slower for [Gd{dtpa(BzA)2}], and almost identical for [Gd{dtpa(BzE)2}]. The analysis of the 1H‐relaxivity of the gadolinium complexes recorded from 0.02 to 300 MHz established that i) the relaxivity of [Gd{dtpa(BzE)2}] is similar to that of [Gd(dtpa)]2−, ii) the slightly slower molecular rotation of [Gd{dtpa(BzA)2}] induces a mild enhancement of its relaxivity, and iii) the marked increase of relaxivity of [Gd{(S)‐(4‐Bz)dtpa}]2− and [Gd{(R)‐(4‐Bz)dtpa}]2− mainly results from an apparently shorter distance between the gadolinium ion and the H2O protons of the coordinated H2O molecule. 相似文献
196.
197.
Wei Cao Jianfeng Jin Gang Wu Nathalie Bravenboer Marco N. Helder Janak L. Pathak Behrouz Zandieh-Doulabi Jolanda M. A. Hogervorst Shingo Matsukawa Lester C. Geonzon Rommel G. Bacabac Engelbert A. J. M. Schulten Jenneke Klein-Nulend 《Molecules (Basel, Switzerland)》2021,26(20)
Current cell-based bone tissue regeneration strategies cannot cover large bone defects. K-carrageenan is a highly hydrophilic and biocompatible seaweed-derived sulfated polysaccharide, that has been proposed as a promising candidate for tissue engineering applications. Whether κ-carrageenan can be used to enhance bone regeneration is still unclear. In this study, we aimed to investigate whether κ-carrageenan has osteogenic potential by testing its effect on pre-osteoblast proliferation and osteogenic differentiation in vitro. Treatment with κ-carrageenan (0.5 and 2 mg/mL) increased both MC3T3-E1 pre-osteoblast adhesion and spreading at 1 h. K-carrageenan (0.125–2 mg/mL) dose-dependently increased pre-osteoblast proliferation and metabolic activity, with a maximum effect at 2 mg/mL at day three. K-carrageenan (0.5 and 2 mg/mL) increased osteogenic differentiation, as shown by enhanced alkaline phosphatase activity (1.8-fold increase at 2 mg/mL) at day four, and matrix mineralization (6.2-fold increase at 2 mg/mL) at day 21. K-carrageenan enhanced osteogenic gene expression (Opn, Dmp1, and Mepe) at day 14 and 21. In conclusion, κ-carrageenan promoted MC3T3-E1 pre-osteoblast adhesion and spreading, metabolic activity, proliferation, and osteogenic differentiation, suggesting that κ-carrageenan is a potential osteogenic inductive factor for clinical application to enhance bone regeneration. 相似文献
198.
Nathalie Schlienger Christian Prigaud Anne-Marie Aubertin Christine Thumann Gilles Gosselin Jean-Louis Imbach 《Helvetica chimica acta》1999,82(11):2044-2051
The in vitro anti-HIV effects and the stability studies of mononucleoside phosphotriester derivatives 1 – 3 of 3′-azido-3′-deoxythymidine (AZT) containing 2-(glucosylthio)ethyl moieties as potential biolabile phosphate-protecting groups are reported. The results of the anti-HIV evaluation demonstrate that the described compounds act via the release of the free nucleoside analogue and cannot be considered as mononucleotide prodrugs (pronucleotides). These data can be related to the lack of substrate affinity of these derivatives towards target-enzymes as corroborated by decomposition studies in various media and experiments with a purified β-D glucosidase. 相似文献
199.
Atiruj Theppawong Tim Van de Walle Dr. Charlotte Grootaert Prof. Dr. Kristof Van Hecke Nathalie Catry Prof. Dr. Tom Desmet Prof. Dr. John Van Camp Prof. Dr. Matthias D'hooghe 《ChemistryOpen》2019,8(2):236-247
Curcumin is known to display pronounced anticancer effects and a variety of other biological activities. However, the low bioavailability and fast metabolism of this molecule present an issue of concern with respect to its medicinal applications. To address this issue, structural modifications of the curcumin scaffold can be envisioned as a strategy to improve both the solubility and stability of this chemical entity, without compromising its biological activities. Previous work in our group targeted the synthesis of symmetrical azaheteroaromatic curcuminoids, which showed better solubility and cytotoxicity profiles compared to curcumin. In continuation of that work, we now focused on the synthesis of non-symmetrical nitrogen-containing curcuminoids bearing both a phenolic and an azaheteroaromatic moiety. In that way, we aimed to combine good solubility, antioxidant potential and cytotoxic properties into one molecule. Some derivatives were selected for further chemical modification of their rather labile β-diketone scaffold to the corresponding pyrazole moiety. In this way, thirteen new non-symmetrical aza-aromatic curcuminoids and four pyrazole-based analogues were successfully synthesized in a yield of 11–69 %. All newly synthesized analogues were evaluated for their antioxidant properties, reactive oxygen species (ROS) production, water solubility and anticancer activities. Several novel derivatives displayed good cytotoxicity profiles compared to curcumin, in combination with an improved water solubility and stability, and were thus identified as potential hit scaffolds for further optimization studies. 相似文献
200.