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31.
D. Hochman Y. Eisenberg A. Engler U. Karshon E.E. Ronat A. Shapira G. Yekutieli 《Nuclear Physics B》1975,89(3):383-404
Cross sections, multiplicities and particle inclusive spectra are presented for π-, K0 and Λ produced in pn reactions at 11.6 GeV/c beam momentum. The results are compared with the data from pp interactions in the same energy range. Correlations between two π- are also discussed. The main results are: the π-, K0 and Λ all behave similarly as a function of transverse momentum squared; π- in the forward c.m. hemisphere have spectra in x and y consistent with that of pp interactions, whereas the spectra of π- in the backward hemisphere fall off more slowly with ∥x∥ and ∥y∥ than those in the forward hemisphere, suggesting n-fragmentation effects. The K0 and Λ have x and y distribution roughly similar to those in pp interactions. The K0 and Λ are consistent with a modified form of KNO scaling. 相似文献
32.
The master equation for the reduced density matrix of the neutral kaon system interacting with a (low temperature) boson gas is derived. The equation is transformed under time reversal (assuming CPT conservation) and the equations of motion in the direct and inverted time schemes are compared. The equations of motion are solved, in a perturbation method, and the explicit approach to thermodynamical equilibrium is described. The entropy production function for the kaonic decaying system is defined and calculated. It is shown that although the equilibrium state and the total entropy change during the approach to it are the same in both time schemes, the details of the entropy time dependence of a coherent initial state are different, thus suggesting a relation between microscopic and macroscopic arrows of time. 相似文献
33.
We propose and analyze a new concept for secure key distribution based on establishing laser oscillations between the sender and receiver. Compared to quantum mechanics based systems, our scheme allows for significantly higher key-establishing rates and longer ranges. By properly designing the laser structure, it is possible to increase the difficulty of eavesdropping almost arbitrarily, thus making our scheme an intriguing alternative and a complementary technology to quantum key-distribution systems. 相似文献
34.
Mason A Agrawal N Washington MT Lesley SA Kohen A 《Chemical communications (Cambridge, England)》2006,(16):1781-1783
An unexpected substrate-dependent lag-phase, found in the single turnover reduction of FDTS bound flavin, sheds light on the molecular mechanism of this alternative thymidylate synthase. 相似文献
35.
Amnon Yekutieli 《代数通讯》2013,41(11):4221-4245
Let A be a noetherian commutative ring, and let 𝔞 be an ideal in A. We study questions of flatness and 𝔞-adic completeness for infinitely generated A-modules. This is done using the notions of decaying function and 𝔞-adically free A-module. 相似文献
36.
Amnon Rosenmann 《代数通讯》2013,41(8):2827-2836
It is not uncommon for rings to have Gabriel localizations which do not possess the unique rank (UR) property although the rings themselves do have UR. We show that if F is a Gabriel filter of right ideals on a ring R and RF is the corresponding Gabriel localization, then free RF?modules of ranks m and n are isomorphic if and only if some F-dense submodule of (R/Tf(R))m is isomorphic to some F-dense submodule of (R/TF(R))n, where TF(R) is the F-torsion ideal of R. 相似文献
37.
Bar-Shir A Avram L Ozarslan E Basser PJ Cohen Y 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,194(2):230-236
q-Space diffusion MRI (QSI) provides a means of obtaining microstructural information about porous materials and neuronal tissues from diffusion data. However, the accuracy of this structural information depends on experimental parameters used to collect the MR data. q-Space diffusion MR performed on clinical scanners is generally collected with relatively long diffusion gradient pulses, in which the gradient pulse duration, δ, is comparable to the diffusion time, Δ. In this study, we used phantoms, consisting of ensembles of microtubes, and mathematical models to assess the effect of the ratio of the diffusion time and the duration of the diffusion pulse gradient, i.e., Δ/δ, on the MR signal attenuation vs. q, and on the measured structural information extracted therefrom. We found that for Δ/δ 1, the diffraction pattern obtained from q-space MR data are shallower than when the short gradient pulse (SGP) approximation is satisfied. For long δ the estimated compartment size is, as expected, smaller than the real size. Interestingly, for Δ/δ 1 the diffraction peaks are shifted to even higher q-values, even when δ is kept constant, giving the impression that the restricted compartments are even smaller than they are. When phantoms composed of microtubes of different diameters are used, it is more difficult to estimate the diameter distribution in this regime. Excellent agreement is found between the experimental results and simulations that explicitly account for the use of long duration gradient pulses. Using such experimental data and this mathematical framework, one can estimate the true compartment dimensions when long and finite gradient pulses are used even when Δ/δ 1. 相似文献
38.
In recent years, much effort has been made to increase our ability to infer nerve fiber direction through the use of diffusion MR. The present study examines the effect of the rotational angle (alpha), i.e. the angle between the diffusion sensitizing gradients and the main axis of the fibers in the nerves, on different NMR indices. The indices examined were the apparent diffusion coefficient (ADC), extracted from low b-values (b(max) approximately 1200 s/mm(2)), and the root mean square (rms) displacement of the fast and the slow-diffusing components extracted from high b-value q-space diffusion MR data. In addition, the effect of both the diffusion time and myelination was evaluated. We found that the most sensitive index to the rotational angle is the rms displacement of the slow-diffusing component extracted from the high b-value q-space diffusion MR experiment. For this component the rms displacement was nearly constant for alpha values ranging from -10 degrees to +80 degrees (where alpha=0 degrees is the z direction), but it changed dramatically when diffusion was measured nearly perpendicular to the nerve fiber direction, i.e., for alpha=90+/-10 degrees. The ADC and the rms displacement of the fast-diffusing component exhibited only gradual changes, with a maximal change at alpha=45+/-15 degrees. The sensitivity of the rms displacement of the slow-diffusing component to the rotational angle was found to be higher at longer diffusion times and in mature fully myelinated nerves. The relevance of these observations for determining the fiber direction is briefly discussed. 相似文献
39.
Crossing fibers, diffractions and nonhomogeneous magnetic field: correction of artifacts by bipolar gradient pulses 总被引:1,自引:0,他引:1
In recent years, diffusion tensor imaging (DTI) and its variants have been used to describe fiber orientations and q-space diffusion MR was proposed as a means to obtain structural information on a micron scale. Therefore, there is an increasing need for complex phantoms with predictable microcharacteristics to challenge different indices extracted from the different diffusion MR techniques used. The present study examines the effect of diffusion pulse sequence on the signal decay and diffraction patterns observed in q-space diffusion MR performed on micron-scale phantoms of different geometries and homogeneities. We evaluated the effect of the pulse gradient stimulated-echo, the longitudinal eddy current delay (LED) and the bipolar LED (BPLED) pulse sequences. Interestingly, in the less homogeneous samples, the expected diffraction patterns were observed only when diffusion was measured with the BPLED sequence. We demonstrated the correction ability of bipolar diffusion gradients and showed that more accurate physical parameters are obtained when such a diffusion gradient scheme is used. These results suggest that bipolar gradient pulses may result in more accurate data if incorporated into conventional diffusion-weighted imaging and DTI. 相似文献
40.
Ephrath Solel Doron Pappo Ofer Reany Tom Mejuch Renana Gershoni-Poranne Mark Botoshansky Amnon Stanger Ehud Keinan 《Chemical science》2020,11(48):13015
Flat corannulene has been considered so far only as a transition state of the bowl-to-bowl inversion process. This study was driven by the prediction that substituents with strong steric repulsion could destabilize the bowl-shaped conformation of this molecule to such an extent that the highly unstable planar geometry would become an isolable molecule. To examine the substituents'' effect on the corannulene bowl depth, optimized structures for the highly-congested decakis(t-butylsulfido)corannulene were calculated. The computations, performed with both the M06-2X/def2-TZVP and the B3LYP/def2-TZVP methods (the latter with and without Grimme''s D3 dispersion correction), predict that this molecule can achieve two minimum structures: a flat carbon framework and a bowl-shaped structure, which are very close in energy. This rather unusual compound was easily synthesized from decachlorocorannulene under mild reaction conditions, and X-ray crystallographic studies gave similar results to the theoretical predictions. This compound crystallized in two different polymorphs, one exhibiting a completely flat corannulene core and the other having a bowl-shaped conformation.The first flat metal-free corannulene derivative was predicted by computations and achieved by synthesis. 相似文献