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941.
Alfredo De Rossi Eric Costard Nicolas Guerineau Sylvain Rommeluere 《Infrared Physics & Technology》2003,44(5-6):325-330
We study the optical coupling in quantum well photodetectors, focusing on finite size effects. We introduced a finite-element model of the detector and we show experimentally that the optical coupling efficiency is strongly dependent on the pixel size and that in very small detectors diffraction dominates the grating coupling. A 640 × 512 QWIP focal plane array was characterized to show that the optical response of thinned samples may depend on the substrate thickness noticeably. These results are in much closer agreement with predictions obtained with our model than using standard techniques. 相似文献
942.
In this paper, we address the problem of curve and surface reconstruction from sets of points. We introduce regular interpolants, which are polygonal approximations of curves and surfaces satisfying a new regularity condition. This new condition, which is an extension of the popular notion of r-sampling to the practical case of discrete shapes, seems much more realistic than previously proposed conditions based on properties of the underlying continuous shapes. Indeed, contrary to previous sampling criteria, our regularity condition can be checked on the basis of the samples alone and can be turned into a provably correct curve and surface reconstruction algorithm. Our reconstruction methods can also be applied to non-regular and unorganized point sets, revealing a larger part of the inner structure of such point sets than past approaches. Several real-size reconstruction examples validate the new method. 相似文献
943.
944.
Mechanistic studies of tandem regioselective decarboxylation, prenyl transfer, and aromatization reactions of prenyl dioxinone diketo-carboxylates to provide 3-prenyl-resorcylate derivatives are described. Studies of the effects of concentration and the base employed as well as the results of cross-over experiments were all found to be consistent with the reaction proceeding largely via an intermolecular reaction pathway. 相似文献
945.
Enzymes are often quantified by measuring their biological activity. Capillary electrophoresis is gaining its position in this field due to the ongoing trend to miniaturize biochemical assays. 相似文献
946.
Intramolecular Hydrogen Bond Reverting the Solvent Effect on Phosphorus Hyperfine Coupling Constants of β‐Phosphorylated Nitroxides
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Prof. Gérard Audran Dr. Lionel Bosco Dr. Paul Brémond Teddy Butscher Prof. Sylvain R. A. Marque Prof. Stéphane Viel 《Chemphyschem》2016,17(23):3954-3963
Recently, we reported a dramatic solvent effect on the phosphorus hyperfine coupling constant aP of β‐phosphorylated six‐membered ring nitroxides, that is, approximately 25 G of difference in aP from n‐hexane to water (Org. Biomol. Chem. 2016 , 14, —1228‐1292). In this article, we report on the effect of intramolecular hydrogen bonding (IHB) in three nitroxides exhibiting IHB between the hydroxyl and diethylphosphoryl groups and one exhibiting IHB between the hydroxyl group and the nitroxyl moiety. It is observed that for the first three nitroxides, aP increases with increasing polarity/polarizability and hydrogen bond donor (HBD) properties of the solvent (π* and α, respectively)—in sharp contrast to the data reported in the literature—and for the last nitroxide, aP decreases with π* and α. In fact, the occurrence of IHB induces a large strain, its suppression by hydrogen bond acceptor (HBA) solvents affords an increase in aP. 相似文献
947.
9‐Silafluorenyl Dichlorides as Chemically Ligating Coupling Agents and Their Application in Peptide Synthesis
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Dr. Samuel J. Aspin Sylvain Taillemaud Patrick Cyr Prof. Dr. André B. Charette 《Angewandte Chemie (International ed. in English)》2016,55(44):13833-13837
A fundamentally simple, mild, and practical procedure for peptide bond formation is reported that employs a stoichiometric amount of easy‐to‐access 9‐silafluorenyl dichlorides as the coupling agent. Without initial preactivation or elaboration of the carboxylic acid or amine termini of the amino acids, the developed reagent is proposed to act through an unprecedented chemical ligation mechanism, bringing the two coupling partners together before being subsequently eliminated. The desired amides or peptide bonds are thus furnished in good yields and with low to no epimerization. 相似文献
948.
Nanoscale Platelet Formation by Monounsaturated and Saturated Sophorolipids under Basic pH Conditions
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Dr. Anne‐Sophie Cuvier Dr. Florence Babonneau Jan Berton Prof. Christian V. Stevens Dr. Giulia C. Fadda Gérard Péhau‐Arnaudet Patrick Le Griel Dr. Sylvain Prévost Dr. Javier Perez Dr. Niki Baccile 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(52):19265-19277
The self‐assembly behavior of the yeast‐derived bolaamphiphile sophorolipid (SL) is generally studied under acidic/neutral pH conditions, at which micellar and fibrillar aggregates are commonly found, according to the (un)saturation of the aliphatic chain: the cis form, which corresponds to the oleic acid form of SL, spontaneously forms micelles, whereas the saturated form, which corresponds to the stearic acid form of SL, preferentially forms chiral fibers. By using small‐angle light and X‐ray scattering (SLS, SAXS) combined with high‐sensitivity transmission electron microscopy imaging under cryogenic conditions (cryo‐TEM), the nature of the self‐assembled structures formed by these two compounds above pH 10, which is the pH at which they are negatively charged due to the presence of a carboxylate group, has been explored. Under these conditions, these compounds self‐assemble into nanoscale platelets, despite the different molecular structures. This work shows that the electrostatic repulsion forces generated by COO? mainly drive the self‐assembly process at basic pH, in contrast with that found at pH below neutrality, at which self‐assembly is driven by van der Waals forces and hydrogen bonding, and thus, is in agreement with previous findings on carbohydrate‐based gemini surfactants. 相似文献
949.
Akane Yamakawa Akinori Takeuchi Yasuyuki Shibata Sylvain Berail Olivier François Xavier Donard 《Accreditation and quality assurance》2016,21(3):197-202
Hg isotopic ratios of NIES CRM No. 13 Human Hair were analyzed using cold vapor generation coupled to multi-collector inductively coupled plasma mass spectrometer to meet the growing demand for better understanding of Hg exposure routes by using Hg isotopic compositions in human hair samples. To validate and assure the accuracy of our analytical method, (1) the reproducibility of the Hg isotopic measurement was monitored and (2) the Hg isotopic compositions of four secondary reference materials—IAEA-085, IAEA-086, and CRPG-RL24H—were measured. Our results for NIES CRM No. 13 show the mass-dependent fractionation values of δ 199Hg = (2.13 ± 0.07) ‰, δ 200Hg = (0.98 ± 0.08) ‰, δ 201Hg = (2.77 ± 0.10) ‰, δ 202Hg = (1.89 ± 0.10) ‰, and δ 204Hg = (2.76 ± 0.16) ‰ (2SD, n = 11) and the mass-independent fractionation values of Δ 199Hg = (1.65 ± 0.06) ‰, Δ 200Hg = (0.04 ± 0.04) ‰, Δ 201Hg = (1.36 ± 0.07) ‰, and Δ 204Hg = (?0.04 ± 0.11) ‰ (2SD, n = 11). Interlaboratory comparison of the CRM performed at the University of Pau showed good agreement with the values obtained at NIES. 相似文献
950.
Sylvain Berns Francisco J. Melndez Hugo Torrens 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(4):268-273
Transition‐metal complexes bearing fluorinated phosphane and thiolate ligands has been an area of study in recent years and the chemical context of the current work is related to the metal‐assisted functionalization of fluorinated derivatives. The cis and trans isomers of the square‐planar complex bis[(pentafluorophenyl)diphenylphosphane‐κP]bis(2,3,5,6‐tetrafluorobenzenethiolato‐κS)platinum(II), [Pt(C6HF4S)2{P(C6H5)2(C6F5)}2], have been crystallized from a single chromatographic fraction and characterized by X‐ray diffraction analysis. The stabilization of the cis isomer results from weak intramolecular π‐stacking interactions and possibly from the formation of a C—F…Pt contact, characterized by an F…Pt separation of 2.957 (6) Å. The natural bond orbital analysis (NBO) for this isomer confirms that the corresponding F → Pt charge transfer accounts for 6.92 kcal mol−1 in the isomer stabilization. Such interactions are not present in the centrosymmetric trans isomer. 相似文献