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101.
L. Barral J. Cano A. J. López J. López P. Nogueira C. Ramírez 《Journal of Thermal Analysis and Calorimetry》1996,47(3):791-797
The diffusive and dynamic mechanical behavior of the DGEBA/1,3-BAC epoxy resin system was studied during water absorption. The diffusion of water was investigated at 100% relative humidity, by immersion of specimens in water at 60, 80 and 100°C. In all absorption experiments, water diffusion followed Fick's law. Diffusion coefficients and saturated water concentrations are given for these temperatures. The activation energy for diffusion was determined from the relationship between the diffusion coefficient and the reciprocal of the absolute temperature. The value obtained was 31.2 kJ mol–1. Dynamic mechanical analysis of samples immersed in 100°C water and with various water contents showed both a shift of Tg, defined by thetan peak, to lower temperatures and a slight decrease in the dynamic modulus in the presence of water. These effects are probably a result of plasticization.This work was supported by the Xunta de Galicia through grant XUGA-17201A92. 相似文献
102.
Duncan?P.?FaggEmail author Vladislav?V.?Kharton Jorge?R.?Frade 《Journal of Solid State Electrochemistry》2004,8(9):618-625
Small (2 mol%) cobalt oxide additions to ceria-gadolinia (CGO) materials considerably improve sinterability, making it possible to obtain ceramics with 95–99% density and sub-micrometre grain sizes at 1,170–1,370 K. The addition of Co causes a significant shift of the electrolytic domain to lower pO2. This modification to the minor electronic conductivity of the electrolyte material has influence on the cathodic oxygen reduction reaction. The impedance technique is shown to provide information not only about polarisation resistance, but also about the active electrode area from analysis of the current constriction resistance. It is demonstrated that this current constriction resistance can be related to the minor electronic contributions to total conductivity in these materials. A simple imbedded grid approach gives control of the contact area allowing the properties of the electrolyte materials to be studied. A much lower polarisation resistance for the Co-containing CGO electrolyte is observed, which can be clearly attributed to an increased three-phase reaction area in the Co-containing material, as a consequence of elevated p-type conductivity. 相似文献
103.
Jorge Labella Gonzalo Durn-Sampedro M. Victoria Martínez-Díaz Toms Torres 《Chemical science》2020,11(39):10778
Here we report gold(i)-catalyzed cycloisomerization as a new powerful synthetic tool for the preparation of π-extended BODIPY derivatives. The catalytic system PPhF3AuCl/AgSbF6 enables the synthesis of [b]-[2,1]naphtho-fused-BODIPYs (2a–2c) under mild conditions, in excellent yields and short reaction times. The reaction is totally regioselective to the 6-endo-dig product and for the α-position of the BODIPY, which is both the kinetically and thermodynamically favored pathway, as supported by the free energy profile calculated by means of Density Functional Theory (DFT). Moreover, this methodology also allows the synthesis of two new families of [b]-aryl-fused-BODIPYs, namely, [3,4]phenanthro- (2e and 2f) and [1,2]naphtho-fused (2g) BODIPYs. Their molecular and electronic structures were established by NMR and UV-vis spectroscopies as well as single-crystal X-ray diffraction analysis. As can be noted from the X-ray structures, 2a, 2e and 2g present interesting structural differences at both the molecular and packing level. Interestingly, despite being isomers, the UV/vis spectra of 2a and 2g revealed significant differences in their electronic structures. The origin of this finding was studied by Time-Dependent DFT calculations. Calculated DFT Nuclear Independent Chemical Shift (NICS(0)) values also supported the different electronic structures of 2a and 2g.Here we report gold(i)-catalyzed cycloisomerization as a new powerful synthetic tool for the preparation of π-extended BODIPY derivatives. 相似文献
104.
Santiago MB Vélez MM Borrero S Díaz A Casillas CA Hofmann C Guadalupe AR Colón JL 《Electroanalysis》2006,18(6):559-572
We present a carbon paste electrode (CPE) modified using the electron mediator bis(1,10‐phenanthroline‐5,6‐dione)(2,2′‐bipyridine)ruthenium(II) ([Ru(phend)2bpy]2+) exchanged into the inorganic layered material zirconium phosphate (ZrP). X‐Ray powder diffraction showed that the interlayer distance of ZrP increases upon [Ru(phend)2bpy]2+ intercalation from 10.3 Å to 14.2 Å. The UV‐vis and IR spectroscopies results showed the characteristic peaks expected for [Ru(phend)2bpy]2+. The UV‐vis spectrophotometric results indicate that the [Ru(phend)2bpy]2+ concentration inside the ZrP layers increased as a function of the loading level. The exchanged [Ru(phend)2bpy]2+ exhibited luminescence even at low concentration. Modified CPEs were constructed and analyzed using cyclic voltammetry. The intercalated mediator remained electroactive within the layers (E°′=–38.5 mV vs. Ag/AgCl, 3.5 M NaCl) and electrocatalysis of NADH oxidation was observed. The kinetics of the modified CPE shows a Michaelis–Menten behavior. This CPE was used for the oxidation of NADH in the presence of Bakers' yeast alcohol dehydrogenase. A calibration plot for ethanol is presented. 相似文献
105.
Ram Manohar & Rajen Kumar Sinha 《计算数学(英文版)》2022,40(2):147-176
This article studies a posteriori error analysis of fully discrete finite element approximations for semilinear parabolic optimal control problems. Based on elliptic reconstruction approach introduced earlier by Makridakis and Nochetto [25], a residual based a posteriori error estimators for the state, co-state and control variables are derived. The space discretization of the state and co-state variables is done by using the piecewise linear and continuous finite elements, whereas the piecewise constant functions are employed for the control variable. The temporal discretization is based on the backward Euler method. We derive a posteriori error estimates for the state, co-state and control variables in the $L^\infty(0,T;L^2(\Omega))$-norm. Finally, a numerical experiment is performed to illustrate the performance of the derived estimators. 相似文献
106.
Becerril Jorge Hermosilla Cristopher 《Journal of Optimization Theory and Applications》2022,194(3):795-820
Journal of Optimization Theory and Applications - In this paper, we provide sufficient optimality conditions for convex optimal control problems with mixed constraints. On one hand, the data... 相似文献
107.
Graciela Díaz de Delgado Ramírez V. Belkis Miguel Delgado José Rosquete P. Carmelo 《Journal of chemical crystallography》1995,25(7):371-374
The title compound, formula C15H20O2, is orthorhombic, P212121 witha=8.747(2),b=12.025(3),c=12.554(3)Å,Z=4, andD
m
=1.32(2)g/ml. The structural analysis shows that the compound corresponds to eudesma-4(15),7(11)-dien-8,12-olide, a sesquiterpene lactone previously isolated fromAster umbellatus but whose crystal structure was unknown. 相似文献
108.
Federico Sánchez-Bringas Ana Irene Ramírez-Galarza 《Annals of Global Analysis and Geometry》1995,13(2):129-140
LetM be a compact orientable surface,I:M R4 an immersion of classC
r
and
a normal unitary smooth vector field. We prove that in the space of pairs (I,
) the family of pairs all whose umbilical points are Darbouxian is generic. 相似文献
109.
Jorge Picado 《Applied Categorical Structures》1994,2(3):297-313
The primary purpose of this paper is to study join-continuous frames. We present two representation theorems for them: one in terms of -subframes of complete Boolean algebras and the other in terms of certain Priestley spaces. This second representation is used to prove that the topological spaces whose frame of open sets is join-continuous are characterized by a condition which says that certain intersections of open sets are open. Finally, we show that Priestley's duality can be viewed as a partialization of the dual adjunction between the categories of, respectively, bitopological spaces and biframes, stated by B. Banaschewski, G. C. L. Brümmer and K. A. Hardie in [5].This work was partially supported by Centro de Matemáíica da Universidade de Coimbra. 相似文献
110.