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101.
Keren K Soen Y Yoseph GB Gilad R Braun E Sivan U Talmon Y 《Physical review letters》2002,89(8):088103
Extensive atomic force and electron microscopy reveal a new, generic DNA-colloid complex with a fixed number of DNA bases per colloid. The fiber shaped complex is stable in the presence of excess colloids in the solution. As more DNA is added to the solution and the ratio between colloids and DNA approaches the fiber's stoichiometry, the system undergoes a sharp coagulation transition. The system is restabilized at even higher DNA concentrations through localization of small colloid clusters on extensive DNA networks. 相似文献
102.
K. Kojima A. Keren L.P. Le M. Larkin G.M. Luke B. Nachumi W.D. Wu Y.J. Uemura M. Azuma M. Takano K. Kiyono S. Miyasaka N. Motoyama H. Takagi S. Uchida M. Hase Y. Sasago K. Uchinokura M. Matsuda K. Katsumata A. Revcolevschi R. Cava 《Hyperfine Interactions》1997,104(1-4):37-42
We introduce our μSR investigations of spin‐gap systems, such as, (1) a 2‐leg spin‐ladder material SrCu2O3, (2) a Haldane material (S=1 spin‐chain) Y2BaNiO5, (3) a spin‐Peierls material CuGeO3, (4) a spin‐chain# material Sr6Ca8Cu24O41. All of these antiferromagnetic spin systems are characterized by a spin‐gap between the singlet ground‐state and the triplet
first excited states. In the above‐mentioned materials, we confirmed the absence of magnetic order down to milli‐Kelvin regime,
supporting the non‐magnetic feature of the ground‐state.
If a spin‐gap system is doped with charges and/or vacancies at the spin site, unpaired spins are induced out of the singlet
ground‐state. In some materials, doping completely destroys the singlet ground‐state and induces a bulk magnetic order. We
report μSR investigations of doped materials as well, which clarifies the existence/absence of a magnetic order upon doping.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
103.
The population inversion in a CO2-He glow discharge has been calculated, taking into account CO produced by dissociation in the discharge. The calculation was based on experimentally determined electron energy distributions and the measured effective relaxation constant of CO2 (001). It is shown that the population inversion is negligible in the absence of CO. 相似文献
104.
A. Keren 《Hyperfine Interactions》1994,85(1):281-286
A new mechanism for positive muon spin-lattice relaxation (SLR) in an antiferromagnet is described. The temperature dependence of the relaxation rate (1/T
1) is calculated in a simplified case, and SLR of muon in MnF2 is studied in the context of this model.The author wishes to thank: S. R. Kreitzman and J. Shaham for their encouragement and stimulating ideas; L. P. Le, G. M. Luke, W. D. Wu, and Y. J. Uemura for helpful discussions. 相似文献
105.
Mendels P Keren A Limot L Mekata M Collin G Horvatic M 《Physical review letters》2000,85(16):3496-3499
We present the first Ga(4f ) NMR study of the Cr susceptibility in the archetype of kagome-based frustrated antiferromagnets, SrCr8Ga4O19. Our major finding is that the susceptibility of the frustrated lattice goes through a maximum around 50 K. Our data also support the existence of paramagnetic "clusters" of spins, responsible for the Curie behavior observed in the macroscopic susceptibility at low T. These results set novel features for the constantly debated physics of geometrically frustrated magnets. 相似文献
106.
We investigate the spin dynamics of SrCr(9p)Ga(12-9p)O19 for p below and above the percolation threshold p(c) using muon spin relaxation. Our major findings are as follows: (i) At T-->0 the relaxation rate is T independent and approximately p(3), (ii) the slowing down of spin fluctuation is activated with an energy U, which is also a linear function of p(3) and lim U as p-->0 = 8 K; this energy scale could stem only from a single ion anisotropy, and (iii) the p dependence of the dynamical properties is identical below and above p(c), indicating that they are controlled by local excitation. 相似文献
107.
Daniel Keren 《Applicable analysis》2013,92(6-7):793-810
Reproduction of kernel Hilbert spaces offers an attractive setting for imaginary time path integrals, since they allow to naturally define a probability on the space of paths, which is equal to the probability associated with the paths in Feynman's path integral formulation. This study shows that if the propagator is Gaussian, its variance equals the squared norm of a linear functional on the space of paths. This can be used to rederive the harmonic oscillator propagator, as well as to offer a finite-dimensional perturbative approximation scheme for the time-dependent oscillator wave function and its ground state energy, and its bound error. The error is related to the rate of decay of the Fourier coefficients of the time-dependent part of the potential. When the rate of decay increases beyond a certain threshold, the error in the approximation over a subspace of dimension n is of order (1/n 3). 相似文献
108.
Carey JR Suslick KS Hulkower KI Imlay JA Imlay KR Ingison CK Ponder JB Sen A Wittrig AE 《Journal of the American Chemical Society》2011,133(19):7571-7576
Rapid identification of both species and even specific strains of human pathogenic bacteria grown on standard agar has been achieved from the volatiles they produce using a disposable colorimetric sensor array in a Petri dish imaged with an inexpensive scanner. All 10 strains of bacteria tested, including Enterococcus faecalis and Staphylococcus aureus and their antibiotic-resistant forms, were identified with 98.8% accuracy within 10 h, a clinically important time frame. Furthermore, the colorimetric sensor arrays also proved useful as a simple research tool for the study of bacterial metabolism and as an easy method for the optimization of bacterial production of fine chemicals or other fermentation processes. 相似文献
109.
Recently, significant progress has been made towards understanding the pathogenesis of cancer from the molecular standpoint. To this end, a growing number of approaches are being exploited for the identification and validation of new therapeutic targets suitable for potent and specific intervention. The type 1 insulin-like growth factor receptor (IGF-1R) system has recently become the focus of major attention in the arena of cancer research. The involvement of the receptor and its downstream signaling cascades in the carcinogenesis process makes this system an excellent target for potential cancer therapy. Indeed, advances in the understanding of the molecular mechanisms behind IGF-1R activation have led to the discovery of agents designed selectively for targeting IGF-1R. The potential application of these inhibitors is currently under intense clinical investigation. This review describes the biology of IGF-1R particularly from a cancer perspective. The attempts to develop effective IGF-1R antagonists are discussed comprehensively with special emphasis on antibodies and small tyrosine kinase inhibitors. 相似文献
110.
Steiner A Szekely P Szekely O Dvir T Asor R Yuval-Naeh N Keren N Kesselman E Danino D Resh R Ginsburg A Guralnik V Feldblum E Tamburu C Peres M Raviv U 《Langmuir : the ACS journal of surfaces and colloids》2012,28(5):2604-2613
Like-charged solid interfaces repel and separate from one another as much as possible. Charged interfaces composed of self-assembled charged-molecules such as lipids or proteins are ubiquitous. The present study shows that although charged lipid-membranes are sufficiently rigid, in order to swell as much as possible, they deviate markedly from the behavior of typical like-charged solids when diluted below a critical concentration (ca. 15 wt %). Unexpectedly, they swell into lamellar structures with spacing that is up to four times shorter than the layers should assume (if filling the entire available space). This process is reversible with respect to changing the lipid concentration. Additionally, the research shows that, although the repulsion between charged interfaces increases with temperature, like-charged membranes, remarkably, condense with increasing temperature. This effect is also shown to be reversible. Our findings hold for a wide range of conditions including varying membrane charge density, bending rigidity, salt concentration, and conditions of typical living systems. We attribute the limited swelling and condensation of the net repulsive interfaces to their self-assembled character. Unlike solids, membranes can rearrange to gain an effective entropic attraction, which increases with temperature and compensates for the work required for condensing the bilayers. Our findings provide new insight into the thermodynamics and self-organization of like-charged interfaces composed of self-assembled molecules such as charged biomaterials and supramolecular assemblies that are widely found in synthetic and natural constructs. 相似文献