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11.
Rijssenbeek JT Saito T Malo S Azuma M Takano M Poeppelmeier KR 《Journal of the American Chemical Society》2005,127(2):675-681
The related parameters of cation size and valence that control the crystallization of Sr(3)CaRu(2)O(9) into a 1:2 B-site-ordered perovskite structure were explored by cationic substitution at the strontium and calcium sites and by the application of high pressure. At ambient pressures, Sr(3)MRu(2)O(9) stoichiometries yield multiphasic mixtures for M = Ni(2+), Mg(2+), and Y(3+), whereas pseudocubic perovskites result for M = Cu(2+) and Zn(2+). For A-site substitutions, an ordered perovskite structure results for Sr(3-x)Ca(x)CaRu(2)O(9), with 0 = x = 1.5. In contrast, Ba(2+) substitution for Sr(2+) is accompanied by a phase change to a hexagonal BaTiO(3) structure type. At high pressures and temperatures, a 1:2 B-site-ordered perovskite structure is stabilized for Sr(3-x)Ba(x)CaRu(2)O(9), with 0 = x = 3. The scarcity of B-site-ordered perovskite ruthenates at ambient pressure and the metastable nature of the high-pressure phases underscore the strict size and valence requirements that must be met by the constituent cations to achieve these uncommon ordered structures. 相似文献
12.
1-(2-Methoxyethoxy)-2-methylbenzene and 1-(2-dimethylaminoethoxy)-2-methylbenzene have been lithiated using sec-BuLi under a variety of conditions and the laterally lithiated species trapped with electrophiles. 相似文献
13.
Jean-Marc Bourgeois 《Helvetica chimica acta》1976,59(6):2114-2124
Treatment of 3-C-cyano-1,2:5,6-di-O-isopropylidene-3-O-(toluene-p-sulfonyl)-α-D -allofurannose with AlLiH4 yields a sugar-spiro-aziridine and a branched chain sulfonamide. Reaction mechanisms are briefly discussed and the configurations of the products obtained are proved by chemical reactions. With hydrogenation, the spiro compound is opened to a branched chain amino sugar with the same tertiary carbon as in vancosamine. Several derivatives of this new compound are described: the 6-deoxy sugars in series L and D and the pentose resulting from its oxidation by periodic acid. The conformation around C(4)–C(5) bond is deduced for three compounds from NMR. data. 相似文献
14.
Robert Lalande Marie-Josphe Bourgeois Bernard Maillard 《Journal of heterocyclic chemistry》1975,12(3):509-511
Di-t-butyl peroxide induces a free radical addition of tetrahydrothiophene to ethylenic compounds. The main products arise from an α-attack of the substrate. This reaction seems to be an interesting synthesis of these heterocycles. 相似文献
15.
Waterman PR Overhaus M Heckenkamp J Nigri GR Fungaloi PF Landis ME Kossodo SC LaMuraglia GM 《Photochemistry and photobiology》2002,75(1):46-50
Restenosis results from intimal hyperplasia and constrictive remodeling following cardiovascular interventions. Photodynamic therapy (PDT) has been shown to inhibit intimal hyperplasia in vivo by preventing neointimal repopulation of the treated vessel. This study was undertaken in an attempt to further dissect the mechanisms by which PDT acts on secreted and extracellular matrix proteins to inhibit migration of cultured human vascular cells. PDT of three-dimensional collagen gels inhibited invasive human smooth muscle cell (SMC) migration, whereas cell-derived matrix metalloproteinase production remained unaltered. Additionally, PDT generated cross-links in the collagen gels, a result substantiated in an ex vivo model whereby PDT rendered the treated vessels resistant to pepsin digestion and inhibited invasive migration of SMC and fibroblasts. These data support the premise that by inducing matrix protein cross-links, rendering the vessel resistant to degradation, in vivo PDT inhibits repopulation of the vessel and therefore intimal hyperplasia. 相似文献
16.
Le Paih J Monnier F Dérien S Dixneuf PH Clot E Eisenstein O 《Journal of the American Chemical Society》2003,125(39):11964-11975
The reaction of a variety of alkynes RCtbd1;CH with a variety of carboxylic acids R(1)CO(2)H, in the presence of 5% of RuCl(COD)C(5)Me(5), selectively leads to the dienylesters (1E,3E)-RCH(1)=CH(2)-CH(3)=C(R)(O(2)CR(1)). The reaction also applies to amino acid and dicarboxylic acid derivatives. It is shown that the first step of the reaction consists of the head-to-head alkyne coupling and of the formation of the metallacyclic biscarbene-ruthenium complex isolated for R = Ph and catalyzing the formation of dienylester. D-labeled reactions show that the alkyne protons remain at the alkyne terminal carbon atoms and carboxylic acid protonates the C(1) carbon atom. QM/MM (ONIOM) calculations, supporting a mixed Fischer-Schrock-type biscarbene complex, show that protonation occurs preferentially at the carbene carbon C(1) adjacent to Ru, in the relative cis position with respect to the Ru-Cl bond, to give a mixed C(1)alkyl-C(4)carbene complex in which the C(4) carbene is conjugated with the noncoordinated C(2)=C(3) double bond. This 16-electron intermediate has a weak stabilizing alpha agostic C-H bond. This most stable isomer appears to have a C(4) center more accessible to the nucleophilic addition which accounts for the experimentally observed product. 相似文献
17.
Choua S Dutan C Cataldo L Berclaz T Geoffroy M Mézailles N Moores A Ricard L Le Floch P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(16):4080-4090
EPR spectra show that one-electron reduction of bis(3-phenyl-6,6-(trimethylsilyl)phosphinine-2-yl)dimethylsilane (1) on an alkali mirror leads to a radical anion that is localized on a single phosphinine ring, whereas the radical anion formed from the same reaction in the presence of cryptand or from an electron transfer with sodium naphthalenide is delocalized on the two phosphinine rings. Density functional theory (DFT) calculations show that in the last species the unpaired electron is mainly confined in a loose P-P bond (3.479 A), which results from the overlap of two phosphorus p orbitals. In contrast, as attested by X-ray spectroscopy, the P-P distance in neutral 1 is large (5.8 A). As shown by crystal structure analysis, addition of a second electron leads to the formation of a classical P-P single bond (P-P 2.389 A). Spectral modifications induced by the presence of cryptand or by a change in the reaction temperature are consistent with the formation of a tight ion pair that stabilizes the radical structure localized on a single phosphinine ring. It is suggested that the structure of this pair hinders internal rotation around the C-Si bonds and prevents 1 from adopting a conformation that shortens the intramolecular P-P distance. The ability of the phosphinine radical anion to reversibly form weak P-P bonds with neutral phosphinines in the absence of steric hindrance is confirmed by EPR spectra obtained for 2,6-bis(trimethylsilyl)-3-phenylphosphinine (2). Moreover, as shown by NMR spectroscopy, in this system, which contains only one phosphinine ring, further reduction leads to an intermolecular reaction with the formation of a classical P-P bond. 相似文献
18.
Sylvie Paycha 《Communications in Mathematical Physics》1995,166(3):433-455
Given a gauge theory with gauge groupG acting on a path spaceX,G andX being both infinite dimensional manifolds modelled on spaces of sections of vector bundles on a compact riemannian manifold without boundary, it is shown that when the action ofG onX is smooth, free and proper, the same ellipticity condition on an operator naturally given by the geometry of the problem yields both the existence of a principal fibre bundle structure induced by the canonical projection :XX/G and the existence of the Faddeev-Popov determinant arising in the functional quantisation of the gauge theory. This holds for certain gauge theories with anomalies like bosonic closed string theory in non-critical dimension and also holds for a class of gauge theories which includes Yang-Mills theory. 相似文献
19.
S. Perries A. Astier L. Ducroux R. Duffait Y. Le Coz M. Meyer N. Redon F. Azaiez S. Bouneau C. Bourgeois R. Collatz I. Deloncle B. J. P. Gall F. Hannachi I. Hibbert A. Korichi A. Lopez-Martens R. Lucas V. Méot N. Poffé M. G. Porquet C. Schück H. Sergolle J. F. Sharpey-Schafer R. Wadsworth A. N. Wilson 《Zeitschrift für Physik A Hadrons and Nuclei》1996,354(1):1-2
The francium isotopes200–202Fr were produced in the reaction35Cl+170Yb using bombarding energies of 4.9–5.3 MeV/nucleon. Fusion products were separated in-flight from the primary beam using
a gas-filled recoil separator. An alpha line with the alpha particle energy and half-life of (7468±9) keV and (19
−6
+13
) ms, respectively, was assigned to200Fr. Previously reported decay properties of201,202Fr were confirmed.
Communicated by V. Metag 相似文献
20.
Lopez-Martens A Hannachi F Dossing T Schück C Collatz R Gueorguieva E Vieu C Leoni S Herskind B Khoo TL Lauritsen T Ahmad I Blumenthal DJ Carpenter MP Gassmann D Janssens RV Nisius D Korichi A Bourgeois C Astier A Ducroux L Le Coz Y Meyer M Redon N Sharpey-Schafer JF Wilson AN Korten W Bracco A Lucas R 《Physical review letters》1996,77(9):1707-1710