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61.
Molality as a unit of measure for expressing 1H MRS brain metabolite concentrations in vivo 总被引:1,自引:0,他引:1
Knight-Scott J Haley AP Rossmiller SR Farace E Mai VM Christopher JM Manning CA Simnad VI Siragy HM 《Magnetic resonance imaging》2003,21(7):787-797
Absolute concentrations of cerebral metabolite in in vivo 1H magnetic resonance spectroscopy studies (1H-MRS) are widely reported in molar units as moles per liter of tissue, or in molal units as moles per kilogram of tissue. Such measurements require external referencing or assumptions as to local water content. To reduce the scan time, avoid assumptions that may be invalid under specific pathologies, and provide a universally accessible referencing procedure, we suggest that metabolite concentrations from 1H-MRS measurements in vivo be reported in molal units as moles per kilogram of tissue water. Using internal water referencing, a two-compartment water model, a simulated brain spectrum for peak identification, and a spectroscopic bi-exponential spin-spin relaxation segmentation technique, we measured the absolute concentrations for the four common 1H brain metabolites: choline (Cho), myo-inositol (mIno), phosphocreatine + creatine (Cr), and N-acetyl-aspartate (NAA), in the hippocampal region (n = 26) and along the Sylvian fissure (n = 61) of 35 healthy adults. A stimulated echo localization method (20 ms echo time, 10 ms mixing time, 4 s repetition time) yielded metabolite concentrations, uncorrected for metabolite relaxation or contributions from macromolecule resonances, that were expectantly higher than with molar literature values. Along the Sylvian fissure the average concentrations (coefficient of variation (CV)) in mmoles/kg of tissue water were 17.6 (12%) for NAA, 14.2 (9%) for Cr, 3.6 (13%) for Cho, and 13.2 (15%) for mIno. Respective values for the hippocampal region were 15.7 (20%), 14.7 (16%), 4.6 (19%), and 17.7 (26%). The concentrations of the two regions were significantly different (p = 0.001) for NAA, mIno, and Cho, a trend in agreement with previous studies. All gray matter Sylvian fissure CV values, except for NAA, were also in agreement with previous 1H-MRS gray matter studies. The reduced precision of the NAA concentration was attributed to overlapping signal contributions from glutamate and glutamine (Glx), suggesting that a detailed Glx model is critical for accurate quantitation of the NAA 2.02 ppm resonance. The reduced precision of the measurements in the hippocampal region was attributed to poor spectral resolution. 相似文献
62.
Cao Thi Vi Ba Ha Huy Bang Dang Van Soa 《International Journal of Theoretical Physics》2003,42(8):1781-1786
We propose commutation relations for a single mode -deformed para-Bose oscillator. In this new deformation of para-Bose statistics the distribution function has the same form as in the para-Bose statistics. Furthermore, we show analogies between the coherent states of -deformed and q-deformed para-Bose statistics. 相似文献
63.
Many graphs arising in various information networks exhibit the "power law" behavior -the number of vertices of degree k is proportional to k-# for some positive #. We show that if # > 2.5, the largest eigenvalue of a random power law graph is almost surely(1+ o(1))?m (1+ o(1))\sqrt{m} where m is the maximum degree. Moreover, the klargest eigenvalues of a random power law graph with exponent # have power law distribution with exponent 2# if the maximum degree is sufficiently large, where k is a function depending on #, mand d, the average degree. When 2<#< 2.5, the largest eigenvalue is heavily concentrated at cm3-# for some constant c depending on # and the average degree. This result follows from a more general theorem which shows that the largest eigenvalue of a random graph with a given expected degree sequence is determined by m, the maximum degree, and [(d)\tilde] \tilde{d} , the weighted average of the squares of the expected degrees. We show that the k-th largest eigenvalue is almost surely (1+ o(1))?{mk} (1+ o(1))\sqrt{m_k} where mk is the k-th largest expected degree provided mk is large enough. These results have implications on the usage of spectral techniques in many areas related to pattern detection and information retrieval. 相似文献
64.
In the late 1950s, B. Segre introduced the fundamental
notion of arcs and complete arcs [48,49]. An arc in a nite
projective plane is a set of points with no three on a line and
it is complete if cannot be extended without violating this
property. Given a projective plane
, determining
, the size of its
smallest complete arc, has been a major open question in finite
geometry for several decades. Assume that
has order
q, it was shown by Lunelli
and Sce [41], more than 40 years ago, that
. Apart from this bound,
practically nothing was known about
, except for the case
is the Galois plane. For
this case, the best upper bound, prior to this paper, was
O(q
3/4)
obtained by Sznyi using the properties of the Galois field
GF(q).In this paper, we prove that
for any projective plane
of order
q, where
c is a universal constant.
Together with Lunelli-Sces lower bound, our result determines
up to a polylogarithmic
factor. Our proof uses a probabilistic method known as the
dynamic random construction or Rödls nibble. The proof also
gives a quick randomized algorithm which produces a small
complete arc with high probability.The key ingredient of our proof is a new concentration
result, which applies for non-Lipschitz functions and is of
independent interest.* Research supported in part by grant RB091G-VU from
UCSD, by NSF grant DMS-0200357 and by an A. Sloan
fellowship.Part of this work was done at AT&T Bell Labs and
Microsoft Research 相似文献
65.
L.H. Nguyen T.V. Phi P.Q. Phan H.N. Vu C. Nguyen-Duc F. Fossard 《Physica E: Low-dimensional Systems and Nanostructures》2007,37(1-2):54
It has been recently demonstrated that carbon nanotubes (CNTs) represent a new type of chemical sensor capable of detecting a small concentration of molecules such as CO, NO2, NH3.In this work, CNTs were synthesized by chemical vapor deposition (CVD) on the SiO2/Si substrate by decomposition of acetylene (C2H2) on sputtered Ni catalyst nanoparticles. Their structural properties are studied by atomic force microscopy, high-resolution scanning electron microscopy (HRSEM) and Raman spectroscopy. The CNTs grown at 700 °C exhibit a low dispersion in size, are about 1 μm long and their average diameter varies in the range 25–60 nm as a function of the deposition time. We have shown that their diameter can be reduced either by annealing in oxygen environment or by growing at lower temperature (less than 600 °C).We developed a test device with interdigital Pt electrodes on an Al2O3 substrate in order to evaluate the CNTs-based gas sensor capabilities. We performed room temperature current–voltage measurements for various gas concentrations. The CNT films are found to exhibit a fast response and a high sensitivity to NH3 gas. 相似文献
66.
Breakdown conditions for creation of the hollow cathode discharge in the nozzle passed through the rf powered electrode and creation of the plasma jet channel in PCVD reactor are studied. Pure nitrogen is used for measurements. The creation of jet channel is easier for smaller rf electrodes. The breakdown depends on the pressure and on the gas inflow rate. The plasma potential and the self-bias potential is influenced by the covering of reactor walls and the rf electrode by a dielectric layer. 相似文献
67.
Trinh An Huy Rameshwar Adhikari Thomas Lüpke Sven Henning Goerg H. Michler 《Journal of Polymer Science.Polymer Physics》2004,42(24):4478-4488
The orientation behavior of isotactic polypropylene (iPP) in α‐ and β‐crystal form was investigated by rheo‐optical Fourier transformed infrared (FTIR) spectroscopy. This method enabled quantification of the degree of orientation as a feature of structural changes during uniaxial elongation in not only the crystalline phase but also the amorphous one. Molecular orientation mechanisms can be successfully derived from experimental results. Generally, three mechanisms were detected for iPP: (1) interlamellar separation in the amorphous phase, (2) interlamellar slip and lamellar twisting at small elongations, and (3) intralamellar slip at high elongations. The third mechanism was favored by α‐PP, whereas β‐PP favored the second mechanism, which, in fact, was responsible for the different mechanical properties of both materials at the macroscopic level. On the other hand, crystallization conditions may have significantly affected the amorphous orientation. Nevertheless, for both iPP types the chains in the amorphous phase always oriented less than did those in the crystalline phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4478–4488, 2004 相似文献
68.
Vu Kim Tuan 《Results in Mathematics》2013,63(1-2):303-309
Boundaries of convex and compact spectra of functions on plane are fully described without passing to the complexification and the Fourier transform. 相似文献
69.
70.