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61.
Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization
in very pure twinned and twin-free NdBa2 Cu3 Oy single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half
the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within
the unit cell and discussed with respect to temperature, field, anisotropy, and twin structure. 相似文献
62.
MJ Lazaro AA Herod M Domin Y Zhuo CA Islas R Kandiyoti 《Rapid communications in mass spectrometry : RCM》1999,13(14):1401-1412
Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
63.
Hafeesudeen Sahabudeen Dr. Haoyuan Qi Marco Ballabio Dr. Miroslav Položij Dr. Selina Olthof Rishi Shivhare Dr. Yu Jing SangWook Park Kejun Liu Dr. Tao Zhang Ji Ma Dr. Bernd Rellinghaus Prof. Dr. Stefan Mannsfeld Prof. Dr. Thomas Heine Prof. Dr. Mischa Bonn Prof. Dr. Enrique Cánovas Prof. Dr. Zhikun Zheng Prof. Dr. Ute Kaiser Dr. Renhao Dong Prof. Dr. Xinliang Feng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(15):6084-6092
Single-layer and multi-layer 2D polyimine films have been achieved through interfacial synthesis methods. However, it remains a great challenge to achieve the maximum degree of crystallinity in the 2D polyimines, which largely limits the long-range transport properties. Here we employ a surfactant-monolayer-assisted interfacial synthesis (SMAIS) method for the successful preparation of porphyrin and triazine containing polyimine-based 2D polymer (PI-2DP) films with square and hexagonal lattices, respectively. The synthetic PI-2DP films are featured with polycrystalline multilayers with tunable thickness from 6 to 200 nm and large crystalline domains (100–150 nm in size). Intrigued by high crystallinity and the presence of electroactive porphyrin moieties, the optoelectronic properties of PI-2DP are investigated by time-resolved terahertz spectroscopy. Typically, the porphyrin-based PI-2DP 1 film exhibits a p-type semiconductor behavior with a band gap of 1.38 eV and hole mobility as high as 0.01 cm2 V−1 s−1, superior to the previously reported polyimine based materials. 相似文献
64.
Selina C. Wang 《Journal of organometallic chemistry》2006,691(21):4386-4392
This brief review describes experimental and theoretical data relevant to the mechanisms of transition metal promoted vinylcyclopropane-cyclopentene rearrangements. In particular, reactions utilizing Pd(0), Rh(I), and Ni(0) are highlighted and compared to analogous reactions not involving transition metals. 相似文献
65.
Selina Yo-Ping Chang Justie Su-Tzu Juan Cheng-Kuan Lin Jimmy J. M. Tan Lih-Hsing Hsu 《Annals of Combinatorics》2009,13(1):27-52
A graph G is hamiltonian connected if there exists a hamiltonian path joining any two distinct nodes of G. Two hamiltonian paths and of G from u to v are independent if u = u
1 = v
1, v = u
v(G)
= v
v(G)
, and u
i
≠ v
i
for every 1 < i < v(G). A set of hamiltonian paths, {P
1, P
2, . . . , P
k
}, of G from u to v are mutually independent if any two different hamiltonian paths are independent from u to v. A graph is k mutually independent hamiltonian connected if for any two distinct nodes u and v, there are k mutually independent hamiltonian paths from u to v. The mutually independent hamiltonian connectivity of a graph G, IHP(G), is the maximum integer k such that G is k mutually independent hamiltonian connected. Let n and k be any two distinct positive integers with n–k ≥ 2. We use S
n,k
to denote the (n, k)-star graph. In this paper, we prove that IHP(S
n,k
) = n–2 except for S
4,2 such that IHP(S
4,2) = 1.
相似文献
66.
67.
To utilize housane-derived cation radicals as intermediates for the synthesis of the bicyclo (n.3.0) framework of natural products, a highly regioselective [1,2] shift of carbon to either a radical or an electron-deficient site is required. Herein we describe how this has been accomplished, provide a set of guidelines to assess housane oxidizability prior to its synthesis, and describe a synthesis of housane 18 that capitalizes upon the facility of [1,5] hydrogen shifts in substituted cyclopentadienes. The catalytic electrochemically mediated oxidation of 18 leads to a cation radical that engages in a rearrangement leading to the (4.3.0) adduct 23. The appearance of a catalytic current in the cyclic voltammogram of a solution containing the tris(aryl)amine and housane 18 is an excellent indicator that the amminium cation radical 14*+ is able to oxidize the housane and return the mediator to the original redox couple. DFT calculations show electron density on both the aryl and strained sigma framework in the HOMO of housane 18. From the spin density and electrostatic potential map for the cation radical, a picture where the spin resides on the side that is distal to the substituent emerges, while the hole is proximal to it. Both experiment and theory show that the rearrangement is best characterized as a [1,2] carbon shift toward an electron-deficient site and that migration toward the substituent-bearing carbon is much preferred over the alternative pathway. 相似文献
68.
A new means-discovered through quantum chemical studies (B3LYP/6-31G(d))-of selectively stabilizing the delocalized forms of unsubstituted semibullvalene and barbaralane is described. Calculations indicate that complexation of delocalized semibullvalene and barbaralane Cope rearrangement transition structures by halogen-containing molecules (homo- and heteronuclear diatomics and Lewis acids) can reduce the barrier significantly, in many cases causing it to disappear entirely. 相似文献
69.
Anastasia A. Selina Sergey S. Karlov Ekaterina V. Gauchenova Andrei V. Churakov Lyudmila G. Kuz'mina Judith A. K. Howard Jörg Lorberth Galina S. Zaitseva 《Heteroatom Chemistry》2004,15(1):43-56
Reactions of element-substituted alkynes R3MCCPh (R3M = Me3Si, Et3Si, Ph3Si, Et3Ge, n-Bu3Sn, N(CH2CH2O)3Si, N(CH2CH2O)3Ge, N(CH2-CHMeO)3Ge, and N(CH2CH2O)2(CH2CHPhO)Ge) with bromine, tetra-n-butylammonium tribromide (TBAT), and N-bromosuccinimide (NBS)/DMSO were investigated. The Z,E-ratio of isomeric dibromoalkenes formed in bromination reaction with Br2 and TBAT are discussed. The crystal structures of N(CH2CH2O)3SiCCPh and N(CH2CHMeO)3GeX (X = C CPh, C(Br)C(Br)Ph, C(Br2)C(O)Ph), and Ph3SiC(Br)C(Br)Ph are reported. © 2003 Wiley Periodicals, Inc. 15:43–56, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.hc10211 相似文献
70.
M.K. Islam S. Biswas N.A. Chowdhury A. Mannan M. Salahuddin AA Mamun 《等离子体物理论文集》2022,62(1):e202100073
A theoretical investigation has been carried out on the propagation of non-linear ion-acoustic shock waves (IASHWs) in a magnetized degenerate quantum plasma system composed of inertial non-relativistic positively charged light and heavy ions, inertialess non-relativistically or ultra-relativistically degenerate electrons and positrons. The reductive perturbation method has been employed to derive the Burgers' equation. It has been observed that under consideration, our plasma model supports only positive potential shock structure. It is also found that the amplitude and steepness of the IASHWs have been significantly modified by the variation of ion kinematic viscosity, oblique angle, number density, and charge state of the plasma species. The results of our present investigation will be helpful for understanding the propagation of IASHWs in white dwarfs and neutron stars. 相似文献