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51.
Dr. Lina María Aguirre‐Díaz Dr. Marta Iglesias Dr. Natalia Snejko Prof. Enrique Gutiérrez‐Puebla Prof. M. Ángeles Monge 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(19):6654-6665
A study on the influence of the cation coordination number, number of Lewis acid centers, concurrent existence of Lewis base sites, and structure topology on the catalytic activity of six new indium MOFs, has been carried out for multicomponent reactions (MCRs). The new indium polymeric frameworks, namely [In8(OH)6(popha)6(H2O)4]?3 H2O ( InPF‐16 ), [In(popha)(2,2′‐bipy)]?3 H2O ( InPF‐17 ), [In3(OH)3(popha)2(4,4′‐bipy)]?4 H2O ( InPF‐18 ), [In2(popha)2(4,4′‐bipy)2]?3 H2O ( InPF‐19 ), [In(OH)(Hpopha)]?0.5 (1,7‐phen) ( InPF‐20 ), and [In(popha)(1,10‐phen)]?4 H2O ( InPF‐21 ) (InPF=indium polymeric framework, H3popha=5‐(4‐carboxy‐2‐nitrophenoxy)isophthalic acid, phen=phenanthroline, bipy=bipyridine), have been hydrothermally obtained by using both conventional heating (CH) and microwave (MW) procedures. These indium frameworks show efficient Lewis acid behavior for the solvent‐free cyanosilylation of carbonyl compounds, the one pot Passerini 3‐component (P‐3CR) and the Ugi 4‐component (U‐4CR) reactions. In addition, InPF‐17 was found to be a highly reactive, recyclable, and environmentally benign catalyst, which allows the efficient synthesis of α‐aminoacyl amides. The relationship between the Lewis base/acid active site and the catalytic performance is explained by the 2D seven‐coordinated indium framework of the catalyst InPF‐17 . This study is an attempt to highlight the main structural and synthetic factors that have to be taken into account when planning a new, effective MOF‐based heterogeneous catalyst for multicomponent reactions. 相似文献
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Caprioara M Fiammengo R Engeser M Jäschke A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(7):2089-2095
In order to expand the repertoire of DNA sequences specifically interacting with transition metals, we report here the first examples of DNA sequences carrying mono- and bidentate phosphane ligands as well as P,N-ligands. Aminoalkyl-modified oligonucleotides have been reacted at predetermined internal sites with carboxylate derivatives of pyrphos, BINAP and phosphinooxazoline (PHOX) 2 b-d. Carbodiimide coupling in the presence of N-hydroxysuccinimide provided the DNA-ligand conjugates in 38-78 % yield. Phosphane-containing oligonucleotides and their phosphane sulfide analogues were characterized by mass spectrometry (MALDI-TOF and FT-ICR-ESI) and their stability after purification and isolation was systematically investigated. While DNA-appended pyrphos ligand was quickly oxidized, BINAP and PHOX conjugates showed high stabilities, making them useful precursors for incorporation of transition metals into DNA. 相似文献
54.
González Iglesias H Fernández Sánchez ML García Alonso JI Sanz-Medel A 《Analytical and bioanalytical chemistry》2007,389(3):707-713
A quantitative methodology has been developed to differentiate between endogenous and supplemented selenium in lactating rats
using two enriched selenium isotopes. Lactating rats were fed for 2 weeks with formula milk containing one enriched Se isotope,
77Se, as the metabolic tracer. The isotopic composition of selenium in serum and urine samples was then measured by collision
cell ICP-MS after the addition of a solution containing another enriched isotope, 74Se, as quantitation tracer, before analysis. Isotope pattern deconvolution allowed the transformation of measured Se isotopic
abundances into concentrations of natural abundance (endogenous) selenium and enriched 77Se (supplemented) present in the samples. The proposed methodology was validated using serum and urine reference materials
spiked with both 77Se and 74Se. The obtained results are discussed in terms of selenium exchange and half-life in lactating rats (11–12 days) and selenium
levels in serum in comparison with non-supplemented rats and control rats after maternal feeding. 相似文献
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Oxygen effects on the EPR signals from wood charcoals: experimental results and the development of a model 总被引:1,自引:0,他引:1
Grinberg OY Williams BB Ruuge AE Grinberg SA Wilcox DE Swartz HM Freed JH 《The journal of physical chemistry. B》2007,111(46):13316-13324
Charcoals prepared from certain tropical woods contain stable paramagnetic centers, and these have been characterized by EPR spectroscopy in the absence and presence of oxygen. The EPR-detectable spin density has been determined, as has been the temperature- and frequency-dependence of the oxygen broadening of the EPR signal, which is orders of magnitude larger than that observed with other materials, such as lithium phthalocyanine. Three Lorentzian components are required to fit the char EPR spectrum in the presence of oxygen, and the oxygen-dependence of the line width, intensity, and resonance position of the three components have been quantified. These results and the properties of porous carbonaceous materials are used to develop a model to explain the effect of oxygen on the char EPR spectral properties. The model is based on oxygen adsorption on the char surface according to a Langmuir isotherm and a dipolar interaction between the paramagnetic adsorbed gas and the charcoal spins. The three EPR components are correlated with the three known classes (sizes) of pores in charcoal, with the largest line broadening attributed to dipolar relaxation of spins in micropores, which have a larger specific surface area and a higher concentration of adsorbed oxygen. An attenuated, but similar, EPR response to oxygen by chars when they are immersed in aqueous solution is attributed to water competition with oxygen for adsorption on the char surface. 相似文献
58.
Diffuse-reflectance Fourier transform-infrared spectroscopic (DRIFT) microanalysis (10 g samples) of a selected series of flavonoids was studied, comparing to transmission FT-IR spectroscopic analysis of the same samples at the mg level. DRIFT was shown to be a useful, sample-saving and reliable IR technique for the structural analysis and compound identification of the mainSilybum genus 3-OH-flavonolignans (silybin, isosilybin, silydianin, silychristin and isosilychristin) and the dihydroflavonol taxifolin. 相似文献
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60.
Rémi Andres Fenggang Sun Dr. Qian Wang Prof. Dr. Jieping Zhu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(1):e202213831
We report herein an asymmetric Pictet–Spengler reaction of α-ketoesters. In the presence of a catalytic amount of simple alanine-derived squaramide and p-nitrobenzoic acid, reaction of tryptamines with methyl 2-oxoalkanoates afforded the corresponding 1-alkyl-1-methoxycarbonyl tetrahydro-β-carbolines (THBCs) in high yields and ee values. A primary kinetic isotope effect (KIE=4.5) using C2-deteurium-labelled tryptamine indicates that rearomatization through deprotonation of the pentahydro-β-carbolinium ion could be the rate- and enantioselectivity-determining step. A concise enantioselective total synthesis of (+)-alstratine A, a hexacyclic cagelike monoterpene indole alkaloid, featuring this reaction as a key step, was subsequently accomplished. Remeasurement of the [a]D value of the natural product indicates that natural alstratine A is dextrorotatory rather than levorotatory as it was initially reported in the isolation paper. 相似文献