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Jaganyi D Tiba F Munro OQ Petrović B Bugarcić ZD 《Dalton transactions (Cambridge, England : 2003)》2006,(24):2943-2949
Substitution reactions of the complexes [Pd(bpma)(H2O)]2+ and [Pt(bpma)(H2O)]2+, where bpma = bis(2-pyridylmethyl)amine, with TU, DMTU and TMTU for both complexes and Cl-, Br-, I- and SCN- for the platinum complex, were studied in aqueous 0.10 M NaClO4 at pH 2.5 using a variable-temperature stopped-flow spectrophotometer. The pKa value for the coordinated water molecule in [Pd(bpma)(H2O)]2+ (6.67) is a unit higher than that of [Pt(bpma)(H2O)]2+. The observed pseudo-first-order rate constants k(obs) (s(-1)) obeyed the equation k(obs) = k2[Nu] (Nu = nucleophile). The second-order rate constants indicate that the Pd(II) complex is a factor of 10(3) more reactive than Pt(II) complex. The nucleophile reactivity attributed to the steric hindrance in case of TMTU and the inductive effect for DMTU was found to be DMTU > TU > TMTU for [Pt(bpma)(H2O)]2+ and DMTU approximately TU > TMTU for [Pd(bpma)(H2O)]2+. The trend for ionic nucleophile was I- > SCN- > Br- > Cl-, an order linked to their polarizability and the softness or hardness of the metal. Activation parameters were determined for all reactions and the negative entropies of activation (Delta S++) support an associative ligand substitution mechanism. The X-ray crystal structure of [Pd(bpma)(py)](ClO4)2 was determined; it belongs to the triclinic space group P1 and has one formula unit in the unit cell. The unit cell dimensions are a = 8.522(2), b = 8.627(2), c = 16.730(4) A; alpha = 89.20(2), beta = 81.03(2), gamma = 60.61(2) degrees ; V = 1055.7(5) A3. The structure was solved using direct methods in WinGX's implementation of SHELXS-97 and refined to R = 0.054. The coordination geometry of [Pd(bpma)(py)]2+ is distorted square-planar. The Pd-N(central) bond distance, 1.996(3) A, is shorter than the other two Pd-N distances, 2.017(3) and 2.019(3) A. The Pd-N(pyridine) distance is 2.037(3) A. 相似文献
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[structure: see text] A spirobisnaphthalene derivative with a new spiro-nonadiene skeleton, spiro-mamakone A (1), has been isolated from the extract of a cultured nonsporulating fungal endophyte derived from the New Zealand native tree Knightia excelsa (rewarewa). The carbon skeleton of spiro-mamakone A represents a new structural entity and an intriguing addition to the structurally diverse spirobisnaphthalene group of compounds. spiro-Mamakone A is potently cytotoxic and is also antimicrobial. 相似文献
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We present a physical- and link-level design for the creation of entangled pairs to be used in quantum repeater applications where one can control the noise level of the initially distributed pairs. The system can tune dynamically, trading initial fidelity for success probability, from high fidelity pairs (F=0.98 or above) to moderate fidelity pairs. The same physical resources that create the long-distance entanglement are used to implement the local gates required for entanglement purification and swapping, creating a homogeneous repeater architecture. Optimizing the noise properties of the initially distributed pairs significantly improves the rate of generating long-distance Bell pairs. Finally, we discuss the performance trade-off between spatial and temporal resources. 相似文献
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The leading asymptotic term for the function that counts theeigenvalues of the Stokes operator is determined for fairlygeneral underlying bounded domains. Moreover, the remainderis estimated in terms of the fractality of the boundary of thedomain. The results obtained resemble corresponding ones forthe Dirichlet Laplacian. 1991 Mathematics Subject Classification:35P20. 相似文献
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Orde Q. Munro Nicole Pearson 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(10):m407-m412
The title salt, (1,4,7,10,13,16‐hexaoxacyclooctadecane‐κ6O)[(isothiocyanato)triphenylborato‐κS]potassium(I), [K(C19H15BNS)(C12H24O6)] or [K(SCNBPh3)(18‐crown‐6)], where 18‐crown‐6 is 1,4,7,10,13,16‐hexaoxacyclooctadecane and [SCNBPh3]− is the (isothiocyanato)triphenylborate anion, exhibits a supramolecular structure that is best described as a helical coordination polymer or molecular screw. This unusual supramolecular structure is based on a framework in which the SCN− ion bridges the chelated K+ ion and the B atom of BPh3 in a μ2 fashion. The X‐ray crystal structure of the title salt has been determined at 100 (1) and 293 (2) K. The K+ ion exhibits axial ligation by the S atom of the [SCNBPh3]− anion, with a K—S distance of 3.2617 (17) Å (100 K). The trans‐axial ligand is an unexpected η2‐bound C=C bond of a phenyl group (meta‐ and para‐C atoms) that belongs to the BPh3 moiety of a neighboring molecule. The K—C bond distances span the range 3.099 (3)–3.310 (3) Å (100 K) and are apparently retained in CDCl3 solution (as evidenced by 13C NMR spectroscopy). By virtue of the latter interaction, the supramolecular structure is a helical coordination polymer, with the helix axis parallel to the b axis of the unit cell. IR spectroscopy and semi‐empirical molecular orbital (AM1) calculations have been used to investigate further the electronic structure of the [SCNBPh3]− ion. 相似文献