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51.
Reaction of the cyanoruthenate anions [Ru(bpym)(CN)4]2- and [[Ru(CN)4]2(mu-bpym)]4- (bpym = 2,2'-bipyrimidine) with lanthanide(III) salts resulted in the crystallization of coordination networks based on Ru-CN-Ln bridges. Four types of structure were obtained: [Ru(bpym)(CN)4][Ln(NO3)(H2O)5] (Ru-Ln; Ln = Sm, Nd, and Gd) are one-dimensional helical chains; [Ru(bpym)(CN)4]2[Ln(NO3)(H2O)2][Ln(NO3)(0.5)(H2O)(5.5)](NO3)(0.5).5.5H2O (Ru-Ln; Ln = Er and Yb) are two-dimensional sheets containing cross-linked chains based on Ru2Ln2(mu-CN)4 diamond units, which are linked into one-dimensional chains via shared Ru atoms; [[Ru(CN)4]2(mu-bpym)][Ln(NO3)(H2O)5]2.3H2O (Ru2-Ln; Ln = Nd and Sm) are one-dimensional ladders with parallel Ln-NC-Ru-CN-Ln-NC strands connected by the bipyrimidine "cross pieces" acting as rungs on the ladder; and [[Ru(CN)4]2(mu-bpym)][Ln(H2O)6](0.5)[Ln(H2O)4](NO3)(0.5).nH2O (Ru2-Ln; Ln = Eu, Gd, and Yb; n = 8.5, 8.5, and 8, respectively) are three-dimensional networks in which two-dimensional sheets of Ru2Ln2(mu-CN)4 diamonds are connected via cyanide bridges to Ln(III) ions between the layers. Whereas Ru-Gd shows weak triplet metal-to-ligand charge-transfer (3MLCT) luminescence in the solid state from the Ru-bipyrimidine chromophore, in Ru-Nd, Ru-Er, and Ru-Yb, the Ru-based emission is quenched, and all of these show, instead, sensitized lanthanide-based near-IR luminescence following a Ru --> Ln energy transfer. Similarly, Ru2-Nd and Ru2-Yb show lanthanide-based near-IR emission following excitation of the Ru-bipyrimidine chromophore. Time-resolved luminescence measurements suggest that the Ru --> Ln energy-transfer rate is faster (when Ln = Yb and Er) than in related complexes based on the [Ru(bipy)(CN)4]2- chromophore, because the lower energy of the Ru-bpym 3MLCT provides better spectroscopic overlap with the low-energy f-f states of Yb(III) and Er(III). In every case, the lanthanide-based luminescence is relatively short-lived as a result of the CN oscillations in the lattice. 相似文献
52.
We construct on S7 an SU(4) invariant solution of d = 11 supergravity in which the metric on the seven-sphere, regarded as a U(1) bundle overCP3, is distorted by stretching the U(1) fibers, and the four-index field strength FMNPQ is non-zero in the S7 directions. This solution presumably corresponds to the SU(4) invariant extremum of the de Wit-Nicolai potential. 相似文献
53.
We discuss the geometry and topology of the complete, non-compact, Ricci-flat Stenzel metric, on the tangent bundle of S
n+1
. We obtain explicit results for all the metrics, and show how they can be obtained from first-order equations derivable from
a superpotential. We then provide an explicit construction for the harmonic self-dual (p, q)-forms in the middle dimension p+q=(n+1) for the Stenzel metrics in 2(n+1) dimensions. Only the (p, p)-forms are L
2
-normalisable, while for (p, q)-forms the degree of divergence grows with . We also construct a set of Ricci-flat metrics whose level surfaces are U(1) bundles over a product of N Einstein-K?hler manifolds, and we construct examples of harmonic forms there. As an application, we construct new examples
of deformed supersymmetric non-singular M2-branes with such 8-dimensional transverse Ricci-flat spaces. We show explicitly
that the fractional D3-branes on the 6-dimensional Stenzel metric found by Klebanov and Strassler is supported by a pure (2,1)-form,
and thus it is supersymmetric, while the example of Pando Zayas-Tseytlin is supported by a mixture of (1,2) and (2,1) forms.
We comment on the implications for the corresponding dual field theories of our resolved brane solutions.
Received: 22 February 2001 / Accepted: 16 August 2002 Published online: 7 November 2002 相似文献
54.
Adaptive phase estimation is the process of estimating the phase of an electromagnetic field via a continually changing measurement. The measurement is varied in an attempt to optimize it at each moment. In this paper, we show that adaptive phase estimation is more accurate than nonadaptive phase estimation for continuous beams of light even when small time delays in the feedback are present. 相似文献
55.
56.
57.
Beavis D Bennett MJ Carroll JB Chiba J Chikanian A Crawford H Cronqvist M Dardenne Y Debbe R Doke T Engelage J Greiner L Hallman TJ Hayano RS Heckman HH Kashiwagi T Kikuchi J Kumar S Kuo C Lindstrom PJ Mitchell JW Nagamiya S Nagle JL Pope JK Stankus P Tanaka KH Welsh RC Zhan W 《Physical review letters》1995,75(17):3078-3081
58.
The tris(phenyltin)-substituted tungstoantimonate(III) Cs6[(PhSn)3Na3(alpha-SbW9O33)2].20H2O (1) and the tetrakis-(phenyltin)-substituted tungstoarsenate(III) Na9[[(PhSn)2O]2H(alpha-AsW9O33)2].20H2O (2) have been prepared by reaction of phenyltin trichloride with Na9[alpha-SbW9O33].19.5H2O and Na9[alpha-AsW9O33].19.5H2O, respectively, in aqueous solution. The products were characterized by elemental analysis, X-ray crystallography, multinuclear NMR, and infrared spectroscopy. Crystals of 1 are monoclinic, space group P2(1)/n, with a = 13.7952(1) A, b = 22.3133(2) A, c = 34.4493(2) A, beta = 90.933(1) degrees, and Z = 4. Anion 1 has nominal D3h symmetry and contains three PhSn3+ groups and three sodium ions sandwiched between [alpha-SbW9O33]9- units. Crystals of 2 are triclinic, space group P1, with a = 15.272(6) A, b = 15.303(6) A, c = 16.760(7) A, alpha = 93.59(3) degrees, beta = 106.187(19) degrees, gamma = 112.23(3) degrees, and Z = 1. Anion 2 has nominal C2h symmetry and contains four PhSn3+ groups sandwiched between two [alpha-AsW9O33]9- units. 相似文献
59.
The crystal and molecular structures of the compounds [(η5-C5H5)Fe(CO)2]2(CH2)n, where 0 n = 3 and 4
Lynn Pope Polly Sommerville Michael Laing Karen J. Hindson John R. Moss 《Journal of organometallic chemistry》1976,112(3):309-324
The crystal stuctures of [(η5-C5H5)Fe(CO)2]2(CH2)n, n = 3 and 4, have been determined.[(η5-C5H5)Fe(CO)2]2(CH2)3: a = 21.20, b = 10.39, c = 7.88Å, β = 101.6°, U = 1699Å3, C2/c, Z = 4, R = 0.059, 1036 observed data.[(η5-C5H5)Fe(CO)2]2(CH2)4: a = 7.63, b = 10.54, c = 21.87Å, β = 96.4°, U= 1748Å3, P21/c, Z = 4, R = 0.051, 1418 observed data.In each compound the iron atoms are joined by simple chains of sigma bonded CH2 groups. Bond lengths are similar in both: mean Fe-CO 1.75, C-O 1.15, FeC(cp) 2.11, FeCH2 2.08, (cp)CC(cp) 1.41, CH2CH2 1.55Å. The (CH2)3 compound retains a 2-fold axis of symmetry in the crystal. The (CH2)4 compound has no imposed symmetry, but closely approximates centrosymmetry. The effects of molecular symmetry on the IR spectrum between 2100 and 1900 cm-1 are discussed. The13C and1H (270 MHz) NMR spectra in solution are shown to be consistent with the structures found crystallographically. 相似文献
60.
The monohydrates of strontium and barium hydroxide have been prepared by decomposition, under vacuum, of the corresponding octahydrates. X-ray powder data for both compounds are reported, together with that for anhydrous strontium hydroxide; the latter is included in order to clarify an apparent anomaly in the literature.
The authors wish to thank Mr. A. Miller for taking the X-ray powder photographs. 相似文献
Zusammenfassung Es wurden die Monohydrate von Strontium und Bariumhydroxid im Vakuum aus den entsprechenden Octahydraten hergestellt. Röntgenographische Daten für beide Verbindungen sowie für wasserfreies Strontiumhydroxid wurden gegeben; für Letzteres, um gewisse Anom alien in der Literatur zu klären.
Résumé Préparation des hydroxydes de strontium et de baryum monohydratés par décomposition dans le vide des octohydrates correspondants. Etude par rayons X de ces composés ainsi que de l'hydroxyde de strontium anhydre, dans le but, pour ce dernier, d'élucider certaines anomalies de la littérature.
, . , ; , .
The authors wish to thank Mr. A. Miller for taking the X-ray powder photographs. 相似文献