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991.
Kellie Brown John Cameron John Stears Wayne Hicky Roger Cormier Xiaoyi Bao Liang Chen 《Fiber and Integrated Optics》2001,20(5):427-442
With OC-192 communications systems being commercially available and higher bit rate systems in development, prudent telecommunications network administrators are testing their installed fibers to determine if they can be successfully used at 10 Gb/s and higher. Together with New Brunswick Telephone (NBTel), the Fiber Optics Group at UNB have tested various installed fibers and cables in the NBTel network for their losses at wavelengths of 1244, 1310, 1550, and 1625 nm, as well as for strain and polarization mode dispersion (PMD). Weather conditions, age, place of installation, and cable types have also been considered. Aging does not seem to affect the performance of the fibers. Although most fibers are high-speed system compatible when looking at attenuation measurements, about 40% of the fibers tested would not meet the 10 Gb/s OC-192 system manufacturer's design guidelines concerning PMD. 相似文献
992.
A. B. D. Brown C. Ferrero T. Narayanan A. R. Rennie 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):481-489
The structure and phase behaviour of a colloidal dispersion of plate-like particles are described. The plates are nickel (II)
hydroxide and have short-range, repulsive interactions and a low polydispersity. As the concentration of the plates is increased,
an equilibrium phase separation between a columnar phase and a less ordered phase is observed. Complementary measurements
using small-angle neutron and small-angle X-ray scattering have been used to distinguish the columnar phase from other possible
ordered structures. Previously isotropic-nematic phase transitions have been observed [#!ref1!#], however this dispersion
forms the more highly ordered columnar phase, due to the aspect ratio and the low polydispersity of the plate-like particles.
The concentration at which phase separation occurs, increases as the range of the particle interactions is reduced. This system
provides an interesting model for comparison with theory and calculations of structures in liquid crystal and mesophase in
which the particle interactions can be altered.
Received 24 February 1999 相似文献
993.
The objective of this case study was to examine the economics of three lignocellulose-to-ethanol conversion technologies:
fast pyrolysis integrated with a fermentation step, simultaneous saccharification and fermentation (SSF), and dilute sulfuric
acid hydrolysis and fermentation. All technologies were assumed to have an annual production rate of 25 million gallons of
ethanol. The three technologies were compared in terms of capital costs, operating costs, and ethanol production costs. Sensitivity
analyses were carried out to study the uncertainties of wood costs and ethanol production rates on ethanol production costs.
Final economic analysis showed that fast pyrolysis integrated with a fermentation step is comparable with the other two processes
and suggests that it should be considered for further development. 相似文献
994.
The effects of complex formation between sodium dodecylsulfate (SDS) and the positively charged (3-(2-methylpropionamide)propyl)trimethyl-ammonium
chloride-acrylamide (MAPTAC-AM) copolymer have been studied in dilute and semidilute aqueous solution in the presence of 10 mM
NaCl. Two different charge densities of the copolymer have been used in the study: 0.31 and 0.66, corresponding to the proportion
of MAPTAC units. Dynamic light scattering (DLS) and rheometry (static low-shear and capillary viscometry) have been performed
on the systems at different charge ratios, i.e., SDS/MAPTAC molar ratios, r. Regarding the phase behavior, the maximum binding ratio prior to precipitation differs between the copolymers. A 1.0% w/v
solution of SDS/31% MAPTAC-AM is soluble at r = 0.4 , while an SDS/66% MAPTAC-AM solution of 1.0% w/v shows phase separation at this ratio. With excess surfactant, the
complex in the former system is resolubilized at r=2.0, whereas the latter system is still phase-separated at r=5.0. DLS results show that, for both copolymers, the hydrodynamic radius, R
h, of the single-chain copolymer-surfactant complex decreases as a function of r, but then increases slightly prior to phase separation. The corresponding hydrodynamic virial coefficient, k
D, changes in the same manner as R
h. The light-scattering data also show that the formation of larger structures is promoted as the polymer concentration is
increased from 0.2 to 1.0% w/v. This is shown by the increase in the relative aggregate-to-single coil peak areas in the relaxation
time distributions. Both systems have this common trend. The results from rheological measurements support the results from
DLS. A reduction in intrinsic viscosity, [η], is observed on increasing r up to phase separation. The major part of the static low-shear measurements showed Newtonian behavior for both systems at
different copolymer concentrations (27.6–138 mM), and at different r. These systems, partially ionic polymer/oppositely charged surfactant, present very interesting rheological behavior at relatively
high polymer concentrations and at low r values. Their behavior is similar to those of hydrophobically modified polyelectrolytes.
Received: 17 June 1998 Accepted: 12 August 1998 相似文献
995.
The acyl endoperoxide arteannuin H, recently reported as a novel natural product from Artemtsia annua, has been obtained in two steps from the photooxidation of dihydroartemisinic acid, thereby confirming biogenetic speculation regarding its derivation from a secondary allylic hydroperoxide. The little studied 3,2-rearrangement reaction of such allylic hydroperoxides is also discussed. 相似文献
996.
Photooxidation of 4-amorphen-11-ol (1), recently reported as one of the major sesquiterpene natural products from the medicinal plant Fabiana imbricata, results in three allylic hydroperoxides 6, 9 and 10, which are expected from the “ene-type” reaction of molecular oxygen with the tri-substituted double bond in 1. The tertiary allylic hydroperoxide 6 undergoes carbon-carbon bond cleavage and a second autoxidation reaction to yield the more highly oxygenated seco-amorphane 11 under very mild conditions. In acid, this compound may then undergo either a second carbon-carbon bond cleavage reaction to yield nor-sesquiterpenes 2 and 3 (reported as bona fide natural products from F. imbricata, or cyclize to the sesquiterpene peroxofabianane (5), which is a presumed precursor to the natural product fabianane (4). Some mechanistic investigations concerning the two chemical processes: viz:- carbon-carbon bond cleavage and autoxidation which would account for the formation of natural products 2, 3 and 4 from 1 are reported. Tertiary allylic hydroperoxide 32, which lacks the 11-hydroxyl functional group present in 1 undergoes only C-4/C-5 carbon-carbon bond cleavage under more forcing conditions, suggesting a role for this functional group in assisting the autoxidation reactions of 4-amorphen-11-ol. 相似文献
997.
Multiplexed piezoresistive sensor arrays hold great potential for measuring contact stress distributions for orthopedic research
applications. However, their acceptance has been handicapped by output drift and the fact that their dynamic response has
not been well characterized. In this report, the static and dynamic responses of one device of this class (the K-Scan piezoresistive
contact stress sensor) are formally characterized using a specially made pressure vessel that provides spatially homogeneous
contact stress. Drift was predominant early in static loading, reaching relationtive errors of approximately 30 percent over
a 10-min period. During loading, first-order dynamic analysis showed that the time constant (and time lag) was nearly zero
and there was little attenuation of the output up to 20 Hz. A deconvolution algorithm proved capable of compensating for the
great majority of static drift. 相似文献
998.
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