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71.
Gago S Pillinger M Valente AA Santos TM Rocha J Gonçalves IS 《Inorganic chemistry》2004,43(17):5422-5431
A Zn,Al layered double hydroxide (LDH) with Zn/Al = 1.45 and containing nitrate anions was prepared by coprecipitation and characterized by powder X-ray diffraction, Zn K-edge extended X-ray absorption fine structure spectroscopy (EXAFS), thermogravimetric analysis, FTIR and FT Raman spectroscopy, and (27)Al MAS NMR spectroscopy. Three Zn...O and four Zn...M (M = Zn, Al) shells could be fitted to the low-temperature (40 K) EXAFS spectrum, in accordance with a model for an ordered cationic sheet. The nitrate anions were easily exchanged by 2,2'-bipyridine-5,5'-dicarboxylate anions, resulting in an increase in the basal spacing from 9 to 18 A. The basal spacing of the pillared derivative indicates that the anions are arranged with their longest dimension nearly perpendicular to the host layers. This material exhibits a high encapsulating ability, as evidenced by its interaction with a dichloromethane solution of the dioxomolybdenum(VI) complex MoO(2)Cl(2)(THF)(2). A material with a metal loading of 11.2 wt % was obtained. Molybdenum K-edge EXAFS analysis could not substantiate the formation of a supported complex of the type MoO(2)Cl(2)(N-N) but instead indicated the formation of unidentate-bridged entities of the type [O(2)Mo-O-MoO(2)] with a metal-metal separation of 3.29 A. The molybdenum-containing LDH was active as a catalyst for the liquid-phase epoxidation of cis-cyclooctene, 1-octene, and trans-2-octene using tert-butyl hydroperoxide as the oxygen source, yielding the corresponding epoxides as the only products. For reactions carried out with no additional solvent (other than n-decane) or in the presence of 1,2-dichloroethane, the solid catalyst could be recycled with no major loss of activity. Other tests confirmed that the systems functioned as true heterogeneous catalysts. 相似文献
72.
V.P. Gonçalves M.V.T. Machado 《The European Physical Journal C - Particles and Fields》2003,29(1):37-44
The heavy quark production in ultraperipheral heavy ion collisions is investigated, with particular emphasis on the results
from the coherent interactions given by the two-photon process. One addresses the heavy quark total cross sections at photon
level considering the saturation model and the BFKL dynamics in the color dipole picture. The corresponding cross sections
at nuclear level are presented. It is verified that the QCD dynamics implies an enhancement of the cross section in comparison
with previous calculations.
Received: 30 January 2003 / Revised version: 26 March 2003 / Published online: 13 May 2003
RID="a"
ID="a" e-mail: barros@ufpel.tche.br
RID="b"
ID="b" e-mail: magnus@if.ufrgs.br 相似文献
73.
A new approach for turbulent fluxes and E×B measurements in the bulk plasma is proposed. It is based in the measurement of fluctuations in the phase velocity of fluctuations. The structure of turbulence has been investigated in the JET plasma boundary region with a fast reciprocating Langmuir probe system. Fluctuations in the radial and poloidal phase velocity have been computed from floating potential and ion saturation current measurements. The correlation between density fluctuations and fluctuations in the radial velocity of fluctuations signals show a good agreement with the turbulent transport computed from the correlation between density and poloidal electric field fluctuations. These results suggest that turbulent transport might be computed in the plasma core from measurement of density fluctuations. E×B sheared flows, both constant and varying in time, are close to the critical value to trigger the transition to improve confinement regimes below the power threshold to trigger the formation of transport barriers. 相似文献
74.
G. M. Caon S. Gonçalves J. R. Iglesias 《The European physical journal. Special topics》2007,143(1):69-74
Simple agent based exchange models are a commonplace in the study of
wealth distribution of artificial societies. Generally, each agent
is characterized by its wealth and by a risk-aversion factor, and
random exchanges between agents allow for a redistribution of the
wealth. However, the detailed influence of the amount of capital
exchanged has not been fully analyzed yet. Here we present a
comparison of two exchange rules and also a systematic study of the
time evolution of the wealth distribution, its functional
dependence, the Gini coefficient and time correlation functions. In
many cases a stable state is attained, but, interesting, some
particular cases are found in which a very slow dynamics develops.
Finally, we observe that the time evolution and the final wealth
distribution are strongly dependent on the exchange rules in a
nontrivial way. 相似文献
75.
José R. B. Gomes Emanuel A. Sousa Jorge M. Gonçalves Luís Gales Ana M. Damas Paula Gomes Siddharth Pandey William E. Acree Jr Maria D. M. C. Ribeiro da Silva 《Journal of Physical Organic Chemistry》2007,20(7):491-498
The gaseous standard molar enthalpies of formation of two 2‐R‐3‐methylquinoxaline‐1,4‐dioxides (R = benzoyl or tert‐butoxycarbonyl), at T = 298.15 K, were derived using the values for the enthalpies of formation of the compounds in the condensed phase, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, using a quartz crystal oscillator. The three dimensional structure of 2‐tert‐butoxycarbonyl‐3‐methylquinoxaline‐1,4‐dioxide has been obtained by X‐ray crystallography showing that the two N? O bond lengths in this compound are identical. The experimentally determined geometry in the crystal is similar to that obtained in the gas‐phase after computations performed at the B3LYP/6‐311 + G(2d,2p) level of theory. The experimental and computational results reported allow to extend the discussion about the influence of the molecular structure on the dissociation enthalpy of the N? O bonds for quinoxaline 1,4‐dioxide derivatives. As found previously, similar N? O bond lengths in quinoxaline‐1,4‐dioxide compounds are not linked with N? O bonds having the same strength. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
76.
Lionel Santinacci Anne-Marie Gonçalves Muriel Bouttemy Arnaud Etcheberry 《Journal of Solid State Electrochemistry》2010,14(7):1177-1184
In this paper, we investigate the properties of porous structures anodically grown onto n-InP (100) in HCl. In situ electrochemical
characterizations show the pore morphology strongly influences the properties of the InP surfaces. Both dc- and ac-electrochemical
measurements reveal an enhancement of the capacitive current and a modification of the electronic distribution at the interface.
Photocurrent spectra performed during the pore growth are also strongly modified. For low anodic charges, an increase of the
photocurrent with a redshift of the absorption edge is measured. These evolutions can be respectively ascribed (i) to a reflection decrease due to a surface roughening and (ii) to the creation of surface states within the band gap. For higher anodic charges, the photocurrent drops with a narrowing
of the spectrum. Using a model based on the “dead” layer, the porous layer is considered as an absorbent film that progressively
attenuates the photocurrent of the bulk semiconductor. 相似文献
77.
Let A be a finitely generated abelian group. We describe the automorphism group Aut(A) using the rank of A and its torsion part p-part A
p
.
For a finite abelian p-group A of type (k
1, ..., k
n
), simple necessary and sufficient conditions for an n × n-matrix over integers to be associated with an automorphism of A are presented. Then, the automorphism group Aut(A) for a finite p-group A of type (k
1, k
2) is analyzed.
This work has begin during the visit of the second author to the Faculty of Mathematics and Computer Science, Nicolaus Copernicus
University during the period July 31–August 13, 2005. This visit was supported by the Nicolaus Copernicus University and a
grant from Cnpq. 相似文献
78.
79.
Carlos F. Pedroso Julcemara G. de Oliveira Francinete R. Campos Alan G. Gon?alves Angela C. L. B. Trindade Roberto Pontarolo 《Chromatographia》2009,69(Z2):201-206
A simple RP–LC method for simultaneous quantification of losartan and amlodipine and separation of their degradation products
has been developed. For this purpose we tested appropriated mobile phase pH range, flow rate, temperature and different columns.
The method was validated with an ODS column. A gradient of acetonitrile and phosphate pH 3.0 buffer was utilized as mobile
phase. The linearity was determined at 50–150% level. Individual recoveries at 70–130% level ranged from 98.8 to 100.5% for
losartan and 96.4–101.2% for amlodipine. The robustness was also evaluated. Although losartan has much higher quantities than
amlodipine in commercial tablets, this method allowed simultaneous quantification for both drugs. 相似文献
80.
Standard enthalpies of solution of t-BuX and CX4 (X=Cl and Br) in several alcohols are reported as measured by a calorimetric method. The corresponding transfer functions from the gas phase were calculated. 相似文献