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141.
Message Delay Analysis for Polling and Token Multiple-Access Schemes for Local Communication Networks 总被引:11,自引:0,他引:11
Two efficient polling (token) schemes, which provide multiaccess coordination for local area networks, are described, analyzed, and compared. The two multiple-access polling protocols described here utilize gated and exhaustive disciplines in ordering the transmission of the messages buffered at each terminal. The delay-throughput performance behavior of polling schemes operating under the above mentioned disciplines is derived. Network terminals are modeled as independent sources, which generate messages in accordance with a renewal process. A queueing theoretic approach is employed in deriving the actual message delay. behavior of both schemes. Several comparisons are presented. Interesting results are obtained when we compare the average message waiting times in the case when the network traffic is completely balanced with the ease when this same traffic is mostly due to a single node. The latter case would arise, for example, m networks employing gateways. 相似文献
142.
Pereira Ernandes B. De Castro Heizir F. De Moraes Flávio F. Zanin Gisella M. 《Applied biochemistry and biotechnology》2001,91(1-9):739-752
The search for an in expensive support has motivated our group to undertake this work dealing with the use of chitosan as
matrix for immobilizing lipase. In addition to its low cost, chitosan has several advantages for use as a support, including
its lack of toxicity and chemical reactivity, allowing easy fixation of enzymes. In this article, we describe the immobilization
of Canada rugosa lipase onto porous chitosan beads for the enzymatic hydrolysis of oliveoil. The binding of the lipase onto the support was
performed by physicalad sorption using hexane as the dispersion medium. A comparativestudy between free and immobilized lipase
was conducted in terms of pH, temperature, and thermal stability. A slightly lower value for optimum pH (6.0) was found for
the immobilized form in comparison with that attained for the soluble lipase (7.0). The optimum reaction temperature shifted
from 37°C for the free lipase to 50°C for the chitosan lipase. The patterns of heat stability indicated that the immobilization
process tends to stabilize the enzyme. The half-life of the soluble free lipase at 55°C was equal to 0.71 h (K
d=0.98 h−1), whereas for the immobilized lipase it was 1.10 h (K
d=0.63 h−1). Kinetics was tested at 37°C following the hydrolysis of olive oil and obeys the Michaelis-Menten type of rate equation.
The K
m was 0.15 mM and the V
max was 51 μmol/(min·mg), which were lower than for free lipase, suggesting that the apparent affinity toward the substrate changes
and that the activity of the immobilized lipase decreases during the course of immobilization. 相似文献
143.
Machado JL Giehl IC Nardi NB dos Santos LA 《IEEE transactions on bio-medical engineering》2011,58(6):1814-1819
Growth of cells in 3-D porous scaffolds has gained importance in the field of tissue engineering. The scaffolds guide cellular growth, synthesize extracellular matrix and other biological molecules, and make the formation of tissues and functional organs easier. The aim of this study is to use α-tricalcium phosphate cement in order to obtain new types of scaffolds with the aid of paraffin spheres as pore generators. The porosity of the scaffolds produced with paraffin spheres was analyzed and compared to the literature, and the study of scaffold permeability using the Forchheimer equation allowed the analysis of pore interconnectivity. In vitro tests showed the behavior of scaffolds in solutions of simulated body fluid, and viability and cell proliferation were also evaluated. The results show the potential use of the materials developed for scaffolds for use in tissue engineering applications. 相似文献
144.
Alex Neves Junior Romildo Dias Toledo Filho Eduardo de Moraes Rego Fairbairn Jo Dweck 《Journal of Thermal Analysis and Calorimetry》2013,113(3):1577-1584
During the formation of pastes, mortar and concretes have been used to capture CO2. This work presents a methodology to estimate the carbon dioxide (CO2) sequestered by high strength and sulfate-resistant Portland cement pastes during their early stages of hydration, by Thermogravimetry and Derivative Thermogravimetry. Water to cement ratio equal to 0.50 and 0.70 were evaluated and the captured CO2 amount was determined through TG/DTG curve data on initial cement mass basis, obtained during accelerated carbonation from the fluid state and accelerated carbonation after a first hydration process. The experiments were performed in a controlled chamber, maintaining the CO2 content at 20 vol % and the temperature at 25 °C, at different relative humidity (RH) (60 and 80 %) ambient. The procedure allows one to estimate the amount of CO2 sequestered by the initial cement mass of a given volume of paste, as well as to evaluate the RH and W/C ratio influence on the amount of hydrated formed products, mainly on the Ca(OH)2, important for CO2 fixation. 相似文献
145.
In this Letter, we introduce a geometric model to explain the origin of the observed shallow levels in semiconductors threaded by a dislocation density. We show that a uniform distribution of screw dislocations acts as an effective uniform magnetic field which yields bound states for a spin-half quantum particle, even in the presence of a repulsive Coulomb-like potential. This introduces energy levels within the band gap, increasing the carrier concentration in the region threaded by the dislocation density and adding additional recombination paths other than the near band-edge recombination. 相似文献
146.
Ziran Wang Zhuang Hao Shifeng Yu Carlos Gustavo De Moraes Leejee H. Suh Xuezeng Zhao Qiao Lin 《Advanced functional materials》2019,29(44)
An ultraflexible and stretchable field‐effect transistor nanosensor is presented that uses aptamer‐functionalized monolayer graphene as the conducting channel. Specific binding of the aptamer with the target biomarker induces a change in the carrier concentration of the graphene, which is measured to determine the biomarker concentration. Based on a Mylar substrate that is only 2.5‐µm thick, the nanosensor is capable of conforming to underlying surfaces (e.g., those of human tissue or skin) that undergo large bending, twisting, and stretching deformations. In experimental testing, the device is rolled on cylindrical surfaces with radii down to 40 µm, twisted by angles ranging from ?180° to 180°, or stretched by extensions up to 125%. With these large deformations applied either cyclically or non‐recurrently, the device is shown to incur no visible mechanical damage, maintain consistent electrical properties, and allow detection of TNF‐α, an inflammatory cytokine biomarker, with consistently high selectivity and low limit of detection (down to 5 × 10?12 m ). The nanosensor can thus potentially enable consistent and reliable detection of liquid‐borne biomarkers on human skin or tissue surfaces that undergo large mechanical deformations. 相似文献
147.
148.
Zanin Gisella M. Kambara Lauro M. Calsavara Luiza P. V. De Moraes Flavio F. 《Applied biochemistry and biotechnology》1994,45(1):627-640
Applied Biochemistry and Biotechnology - Saccharification of α-amylase liquefied cassava starch was carried out at pH 4.5 and 45?C, in both fixed and fluidized bed reactors, using... 相似文献
149.
Summary A derivation of spectral energy functions for stable atmospheric boundary layers is presented for a local similarity regime.
Previous studies of this nocturnal atmospheric conditions were usually carried through purely kinematic modellizations. In
this study, the atmospheric turbulence energy content is derived from a dynamical viewpoint. This is achieved through the
use of the energy balance relation obtained by Rotta from Navier-Stokes equations. The result is an appropriate physical rooting
of the spectral energy curves known as Kaimal’s Isopleths.
The authors of this paper have agreed to not receive the proofs for correction. 相似文献
150.