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61.
J.?E.?Madriz AguilarEmail author M.?Bellini 《The European Physical Journal C - Particles and Fields》2004,38(3):367-371
We develop a 5D mechanism, inspired by Campbells theorem, to explain the (neutral scalar field governed) evolution of the universe from an initially inflationary expansion that has a change of phase towards a decelerated expansion and thereafter evolves towards the present day observed accelerated (quintessential) expansion.Received: 4 October 2004, Published online: 23 November 2004PACS:
04.20.Jb, 11.10.Kk, 98.80.Cq 相似文献
62.
Nonlocal shaping effects in the time or spectral profiles of an entangled photon pair emerging from a pulsed parametric down-converter are observed by spectrally or temporally filtering one of the twin beams. In particular, we demonstrate the appearance of fourth-order ("ghost") interference fringes in the spectrum of one beam conditioned by photodetection at the output of an unbalanced Michelson interferometer placed in the path of the other beam. The coherence time of the pump is the limiting factor for the sharpness of the details in the shaped biphoton spectrum. 相似文献
63.
Bellini T Buscaglia M Chiccoli C Mantegazza F Pasini P Zannoni C 《Physical review letters》2000,85(5):1008-1011
It is now generally accepted that even low amounts of quenched disorder disrupt long-range order in anisotropic systems with continuous symmetry. However, very little is known on the key item of the nature of the residual order, if any, and particularly if this has quasi-long-range or truly-short-range character. Here we address this problem both experimentally for the nematic 6CB in dilute aerosils and with computer simulations. We find that the residual order is short ranged and scales with disorder density in agreement with the Imry-Ma argument. 相似文献
64.
A.T. Abrosimov G. Bellini L.P. Chernenko M. Di Corato G.I. Drondina P.L. Frabetti Yu.I. Ivanshin P. Laurikainen L.K. Litkin V.P. Lobanova E. Meroni S. Michelletti V.A. Moiseenko V.I. Nikanorov S. Otwinowski Z. Otwinowski F. Palombo M. Pernicka O.A. Zaimidoroga 《Nuclear Physics B》1979,158(1):11-28
Multiparticle production in π?-nucleus interactions at 40 GeV/c (Fifth Joint CERN-Serpukhov Experiment) has been studied using a spark-chamber technique at the Serpukhov accelerator. The mean multiplicities, the pseudorapidity distributions and the dispersion of the multiplicity distributions of charged particles produced on C, Al, Cu and Pb targets are presented. The data have been analysed, both subtracting and including secondary protons with p < 1 GeV/c. In the region of pseudorapidity η > 3.4 the average multiplicity is nearly independent of the size () of the target nucleus, while it increases for η < 3.4. In the forward direction (η > 4) the mean multiplicity on nuclei is smaller than the mean multiplicity on hydrogen. The dependence upon in the target fragmentation region is stronger when the emitted protons are included in the pseudorapidity distributions of the secondary particles. The dispersion of the multiplicity distributions for the different nuclear targets versus the mean multiplicity shows the same slope as found by the world statistics on hydrogen and by other experiments on nuclei at different energies. The results are compared with the predictions of the coherent tube model and with the soft hadron-nucleus collision model. 相似文献
65.
Mauricio Bellini 《General Relativity and Gravitation》2002,34(11):1953-1961
I study a fresh inflationary model with a scalar field nonminimally coupled to gravity. An example is examined. I find that, as larger is the value of p (a t
p
), as smaller (but larger in its absolute value) is the necessary value of the coupling to the inflaton field fluctuations can satisfy a scale invariant power spectrum. 相似文献
66.
Bellini T Buscaglia M Chiccoli C Mantegazza F Pasini P Zannoni C 《Physical review letters》2002,88(24):245506
Nematics with quenched disorder have been repeatedly predicted to form glass phases. Here we present turbidity experiments and computer simulations aimed at studying glass key features such as dynamics and history dependence in randomly perturbed nematics. Electric field-cooling alignment has been employed to prepare samples in suitably oriented starting states. Remarkable remnant order and slow dynamics are found both by experiment and simulations, indicating that random disorder can, by itself, induce a nematic glass state even without perturber restructuring. 相似文献
67.
Mauricio Bellini 《General Relativity and Gravitation》2001,33(1):127-143
A second-order expansion for the quantum fluctuations of the matter field was considered in the framework of the warm inflation scenario. The friction and Hubble parameters were expanded by means of a semiclassical approach. The fluctuations of the Hubble parameter generates fluctuations of the metric. These metric fluctuations produce an effective term of curvature. The power spectrum for the metric fluctuations can be calculated on the infrared sector. 相似文献
68.
69.
Diana Salazar Illera Surisetti Suresh Maria Moccia Gea Bellini Michele Saviano Mauro F.A. Adamo 《Tetrahedron letters》2012,53(14):1808-1811
We describe the development of an N-heterocyclic carbene catalysed homoenolate addition to 4-nitro-5-styrylisoxazoles to give substituted cyclopentanones with a unique substitution pattern and as single diastereoisomers. The synthetic utility of the cyclopentanones obtained was briefly explored through their conversion into α-fluorinated diketones and keto acids. 相似文献
70.
Sequential Barium‐Catalysed N−H/H−Si Dehydrogenative Cross‐Couplings: Cyclodisilazanes versus Linear Oligosilazanes
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Clément Bellini Dr. Thierry Roisnel Prof. Dr. Jean‐François Carpentier Dr. Sven Tobisch Dr. Yann Sarazin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15733-15743
Starting from Ph3SiH, the barium precatalyst Ba[CH(SiMe3)2]2?(THF)3 was used to produce the disilazane Ph3SiN(Bn)SiPh2NHBn ( 4 ) by sequential N?H/H?Si dehydrogenative couplings with BnNH2 and Ph2SiH2. Substrate scope was extended to other amines and hydrosilanes. This smooth protocol gives quantitative yields and full chemoselectivity. Compound 4 and the intermediates Ph3SiNHBn and Ph3SiN(Bn)SiHPh2 were structurally characterised. Further attempts at chain extension by dehydrocoupling of Ph2SiH2 with 4 instead resulted in cyclisation of this compound, forming the cyclodisilazane c‐(Ph2Si‐NBn)2 ( 5 ) which was crystallographically authenticated. The ring‐closure mechanism leading to 5 upon release of C6H6 was determined by complementary experimental and theoretical (DFT) investigations. Ba[CH(SiMe3)2]2?(THF)3 and 4 react to afford the reactive Ba{N(Bn)SiPh2N(Bn)SiPh3}2, which was characterised in situ by NMR spectroscopy. Next, in a stepwise process, intramolecular nucleophilic attack of the metal‐bound amide on the terminal silicon atom generates a five‐coordinate silicate. It is followed by turnover‐limiting β‐C6H5 transfer to barium; this releases 5 and forms a transient [Ba]?Ph species, which undergoes aminolysis to regenerate [Ba]?N(Bn)SiPh2N(Bn)SiPh3. DFT computations reveal that the irreversible production of 5 through such a stepwise ring‐closure mechanism is much more kinetically facile (ΔG≠=26.2 kcal mol?1) than an alternative σ‐metathesis pathway (ΔG≠=48.2 kcal mol?1). 相似文献