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121.
An original polyamine, 2,3 di-2-aminomethyl 1,4 diaminobut-2-ene (ten), characterized by single-crystal XRD analysis, has been synthesised and leads to a new hybrid fluoroaluminate [H4ten] · (AlF5)2 by microwave heating assisted hydrothermal synthesis. The structure of [H4ten] · (AlF5)2 is ab initio determined from powder data. 相似文献
122.
Irene Schlnvogt Stefan Pitsch Catherine Lesueur Albert Eschenmoser Bernhard Jaun Romain M. Wolf 《Helvetica chimica acta》1996,79(8):2316-2345
The solution structure of the duplex formed by self-pairing of the p-RNA octamer β-D -ribopyranosyl-(2′→4′)-(CGAATTCG) was studied by NMR techniques and, independently, by molecular-dynamics calculations. The resonances of all non-exchanging protons, H-bearing C-atoms, P-atoms, and of most NH protons were assigned. Dihedral angle and distance constraints derived from coupling constants and NOESY spectra are consistent with a single dominant conformer and corroborate the main structural features predicted by qualitative conformational analysis. The duplex displays Watson-Crick pairing with antiparallel strand orientation. The dihedral angles β and ? in the phosphodiester linkages differ considerably from the idealized values. Model considerations indicate that these deviations from the idealized model allow better interstrand stacking and lessen unfavorable interactions in the backbone. The average base-pair axis forms an angle of ca. 40° with the backbone. The resulting interstrand π-π stacking between either two purines, or a purine and a pyrimidine, but not between two pyrimidines, constitutes a characteristic structural feature of the p-RNA duplex. A 1000-ps molecular-dynamics (MD) calculation with the AMBER force field resulted in an average structure of the same conformation type as derived by NMR. For the backbone torsion angle ?, dynamically averaged coupling constants from the MD calculation agree well with the experimental values, but for the angle β, a systematic difference of ca. 25° remains. The two base pairs at the ends of the duplex are calculated to be highly labile, which is consistent with the high exchange rate of the corresponding imino protons found by NMR. 相似文献
123.
Gunnlaugsson T Brougham DF Fanning AM Nieuwenhuyzen M O'Brien JE Viguier R 《Organic letters》2004,6(26):4805-4808
[reaction: see text] The macrocyclic cyclen conjugates 1-4 were synthesized with the aim of forming lanthanide ion-based macrocyclic conjugates possessing deep cavities, formed upon complexation to various lanthanide ions. These complexes all possess metal-bound water molecules, where the pKa of the water molecules depends on the nature of the cavity. 相似文献
124.
Richeter S Jeandon C Kyritsakas N Ruppert R Callot HJ 《The Journal of organic chemistry》2003,68(24):9200-9208
We describe the preparation of six diketones based on the frameworks of five bis-naphthoporphyrins and one perinaphthoporphyrin. All diketones derive from meso-tetraarylporphyrins having incorporated two carbonyl groups, each one connected to one beta-pyrrole carbon and one ortho carbon atom from a meso-aryl group. These compounds were all produced in good yield by intramolecular Friedel-Crafts acylation, either from porphyrins meso-substituted by o-carboxyphenyl or o,o'-dicarboxyphenyl substituents or from porphyrins bearing carboxy groups attached to the pyrrolic beta-positions. Although the former reaction does not show significant regioselectivity when run on nickel complexes, the opposite is true for the corresponding free bases. All diketones show a spectacular bathochromic shift of the UV-vis absorption, the longest wavelength bands absorbing in the 700-825 nm range. Two compounds were structurally characterized by X-ray diffraction. In the case of the diketone, whose carbonyl groups are attached to vicinal pyrrolic beta-positions, a significant intermolecular interaction between the two carbonyl groups and an aromatic hydrogen atom was detected. 相似文献
125.
J. Saudraix D. Denegri M. Loret L. Mosca J. C. Scheuer Z. Strachman I. V. Ajinenko Y. A. Belokopitov P. V. Chliapnikov P. A. Gorbunov V. N. Riadovikov A. P. Vorobjev C. Dujardin F. Grard J. Laurent R. Windmolders M. Barth E. A. De Wolf F. Verbeure France-Soviet Union Collaboration CERN-Soviet Union Collaboration 《Zeitschrift fur Physik C Particles and Fields》1980,5(2):105-116
We study single and double inclusive diffractive production in a 32 GeV/c K + p experiment in MIRABELLE at the Serpukhov accelerator. From reactionsK + p→K ++X + andK + p→X ++p we determine the total proton and kaon single diffractive dissociation cross sections \(\sigma (p\xrightarrow{{K^ + }}p_D ) = 0.90 \pm 0.12 mb\) and \(\sigma (K^ + \xrightarrow{p}K_D^ + ) = 0\) . 90±0.17 mb, respectively. In either case the only notable contributions come from dissociations into 1 and 3 charged particles. Kaon dissociation exhibits a pronounced slope-mass correlation. The search for double diffractive production in reactionsK + p→(K +π?π+)+X + andK + p→(pπ + π ?)+X + leads in either case to an estimated total double diffractive cross section σ(K +p→K D + pD) of ?220 μb. The double dissociation differential cross section exhibits a large slope of ?10GeV?2 in the nearthreshold mass region, rapidly decreasing to ?4 GeV?2 with increasing excitation mass. At our c.m. energy \((\sqrt s \simeq 8 GeV)\) the ratio σinel dif/σel is 0.85±0.10, the total diffractive cross section σdif≡σel+σinel dif=4.41±0.24 mb and the fraction σdif(K + p)/σtot(K + p) is 25±2%. TheK + andK ? diffractive excitation mass spectra, differential cross sections and total diffractive cross sections are very similar for both single and double dissociations. 相似文献
126.
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128.
Nicolas Gigant Laëtitia Chausset-Boissarie Romain Rey-Rodriguez Isabelle Gillaizeau 《Comptes Rendus Chimie》2013,16(4):358-362
Direct C(3) alkenylation of non-aromatic enamides through palladium(II)-catalyzed Fujiwara–Moritani cross-coupling was developed. The reaction scope includes a range of cyclic enamides as well as activated alkenes. The utility of this methodology is illustrated by the synthesis of octa- or tetrahydroquinoline cores obtained from conjugated enamides via Diels–Alder cycloaddition. 相似文献
129.
130.
Influence of the particle size of the MgCl2 support on the performance of Ziegler catalysts in the polymerization of ethylene to ultra‐high molecular weight polyethylene and the resulting polymer properties
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An Philippaerts Richard Ensinck Nicolas Baulu Astrid Cordier Kersten Woike Romain Berthoud Gert De Cremer John R. Severn 《Journal of polymer science. Part A, Polymer chemistry》2017,55(16):2679-2690
A highly systematic size series of Ziegler catalysts with similar porosities and surface textures are synthesized by varying the stirring speed during the MgCl2 support synthesis. Besides the mean particle size, the only substantial difference observed between the various catalysts is the size and number of nodules per particle. Varying the mean diameter of the catalyst particles between 1.5 and 11.9 µm, leads to a pronounced impact on the activity in ultra‐high molecular weight polyethylene (UHMWPE) polymerization, while the Mw capabilities are only affected to a limited extend. In addition, it is observed that both the Mws as the polymer bulk density (BD) increases during the course of the polymerization. This particularity allows to optimize the Mw and/or BD at a set polymer size, by tuning the catalyst particle size. This is particularly interesting in UHMWPE production, as control of the morphological and structural properties of the UHMWPE reactor powders are critical for efficient processing as well as the performance of the final product. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2679–2690 相似文献