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排序方式: 共有197条查询结果,搜索用时 15 毫秒
1.
Since the outbreak of the COVID-19 pandemic, most countries have recommended their citizens to adopt social distance, hand hygiene, and face mask wearing. However, wearing face masks has not been well adopted by many citizens. While the reasons are complex, there is a general perception that the evidence to support face mask wearing is lacking, especially for the general public in a community setting. Face mask wearing can block or filter airborne virus-carrying particles through the working of colloid and interface science. This paper assesses current knowledge behind the design and functioning of face masks by reviewing the selection of materials, mask specifications, relevant laboratory tests, and respiratory virus transmission trials, with an overview of future development of reusable masks for the general public. This review highlights the effectiveness of face mask wearing in the prevention of COVID-19 infection. 相似文献
2.
Ewa Dabek-Zlotorzynska Maria Piechowski Fang Liu Scott Kennedy Joseph F. Dlouhy 《Journal of chromatography. A》1997,770(1-2):349-359
Capillary electrophoresis (CE) with indirect UV detection utilizing a pyromellitate-based electrolyte was used for the routine analysis of major anions in atmospheric aerosols collected on filters with high-volume (Hi-Vol) samplers. The long-term reliability of the CE system was checked over an 8-month period during which over 2900 samples were analyzed. In addition, approximately 1100 samples were analyzed in parallel by ion chromatography (IC). It has been shown that acceptable analytical performance can be routinely obtained. The agreement between the CE and IC results is good, generally better than 20% at concentrations larger than 1 mg l−1. 相似文献
3.
John Liggio Robert Mclaren 《International journal of environmental analytical chemistry》2013,93(10):819-835
A method has been developed to measure aldehydes and ketones associated with atmospheric particles. Carbonyl compounds from particulate material collected on Teflon-coated glass-fiber filters were simultaneously extracted and derivatized with an appropriate 2,4-dinitrophenylhydrazine (2,4-DNPH) solution. The efficiency of this procedure utilizing various 2,4-DNPH concentrations and solvent compositions was studied for 13 carbonyl compounds of atmospheric importance. These include formaldehyde, acetaldehyde, acetone, dicarbonyls such as glyoxal and methylglyoxal, and biogenic carbonyls such as pinonaldehyde and nopinone. An extraction solution containing 3 × 10?2 M 2,4-DNPH, in 60% acetonitrile/40% water, and pH 3 was most efficient in extracting and derivatizing these aldehydes and ketones (83-100% recovery). Improved sample enrichment and 2,4-DNPH purification methods were developed that afforded detection limits of 0.009-5.6 ng m?3. The relative standard deviation for replicate analyses were 1.9-10.1%. Carbonyl compounds in ambient particulate samples were quantified during a recent field study. Median values for nine carbonyl species ranged from 0.01-33.9 ng m?3 during the study. 相似文献
4.
V. Parfait-Pignol G. Le Caër R. Delannay 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):499-511
The topological and metric properties of a few natural 2D random cellular structures, namely an armadillo shell structure
and young soap froths, which are formed from two classes of cells, large and small, have been characterized. The topological
properties of a model generated from a Kagome tiling, which mimics such random binary structures, have also been exactly calculated.
The distribution of the number of cell sides is bimodal for the structures investigated. In contrast to the classical Aboav-Weaire
law for homogeneous 2D random cellular structures, nm(n), the mean total number of edges of neighbouring cells of cells with n sides does not vary linearly with n. Only the nm(i, n) (i=1,2) determined separately for every class of cells are linear in n for all investigated structures. Topological properties and correlations between metric and topological properties are finally
compared with the predictions of various literature models.
Received: 24 December 1997 / Revised: 7 April 1998 / Accepted: 20 April 1998 相似文献
5.
Experiments by Gittings, Bandyopadhyay and Durian (Europhys. Lett. 65, 414 (2004)) demonstrate that light possesses a higher probability to propagate in the liquid phase of a foam due to total
reflection. The authors term this observation photon channelling which we investigate in this article theoretically. We first
derive a central relation in the work of Gitting et al. without any free parameters. It links the photon's path-length fraction f in the liquid phase to the liquid fraction ɛ. We then construct two-dimensional Voronoi foams, replace the cell edges by
channels to represent the liquid films and simulate photon paths according to the laws of ray optics using transmission and
reflection coefficients from Fresnel's formulas. In an exact honeycomb foam, the photons show superdiffusive behavior. It
becomes diffusive as soon as disorder is introduced into the foams. The dependence of the diffusion constant on channel width
and refractive index is explained by a one-dimensional random-walk model. It contains a photon channelling state that is crucial
for the understanding of the numerical results. At the end, we shortly comment on the observation that photon channelling
only occurs in a finite range of ɛ. 相似文献
6.
We have experimentally studied the dissociation/coalescence of internal Plateau borders (PBs) in simple monolayer bubble clusters, as a result of changing the liquid fraction. At large liquid content, the clusters consist of n bubbles of the same size, symmetrically placed around an internal n-sided PB (n-PB). On decreasing the liquid fraction we observed symmetry-breaking transitions in the 4- and 5-bubble clusters (but not in the 3-bubble cluster), followed by dissociation of the PBs. We used the Surface Evolver to determine the various equilibrium configurations of the corresponding two-dimensional wet clusters and their surface energies. The sequence of 4-bubble cluster configurations observed on varying the liquid fraction correlates qualitatively with that predicted on the basis of Surface Evolver calculations. The same is not true of the 5-bubble cluster. 相似文献
7.
8.
Bohn S 《The European physical journal. E, Soft matter》2003,11(2):177-189
We present an experimental and theoretical investigation
of a system composed of two soap bubbles strained between two
parallel solid surfaces. The two-bubble cluster can be found in
several configurations. The existence and stability of each of
these states is studied as a function of the distance between
the two facing surfaces. The change of this distance can induce
a transition from one configuration to another; we observe that
most transitions are subcritical, showing that the system is
often trapped in states where the minimum of free energy is only
local. The hysteretic transitions are responsible for the
dissipation of elastic energy. The existence of more than one
stable states for given boundaries conditions combined with the
absence of thermalization means that the history of the system
has to be taken into account and that there is no unique
stress-strain relation. In the present system, because of its
simplicity, a complete quantitative analysis of these general
processes is obtained. The presented results may contribute to a
better understanding of the dynamics of more complex systems
such as foams or granular materials where similar processes are
at work. 相似文献
9.
Predicting potential changes in groundwater salinity in low-lying coastal regions due to climate change is important, where coastal vegetation is abundant, succession competition between halophytes and glycophytes plays a significant role in the salinity budget. Sea level rise enhances salinity intrusion, contributing an additional dimension to vegetation competition. A new simulation model known as mangrove-hardwood hammock model coupled with saturated-unsaturated transport (MANTRA) has recently been developed by the authors to simulate groundwater salinity regimes in the presence of vegetation competition, subject to climate change. MANTRA is based upon linking two existing Unites States geological survey (USGS) simulation models known as mangrove-hardwood hammock model (MANHAM) and saturated-unsaturated transport (SUTRA). MANHAM simulates the evolution of vegetation succession subject to changing groundwater salinity. SUTRA simulates saturated and unsaturated transport of solutes and salinity in groundwater given sea salinity. MANTRA improves the simulation robustness to simultaneously simulate groundwater hydrology, salinity and coastal vegetation succession subject to sea level rise. Some simulation results will be presented to demonstrate the impact of sea level rise on coastal vegetation succession and groundwater salinity. 相似文献
10.
Chih-Wei Chiang Subrata Kumar Das 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(7):1187-1195
The aerosol optical thickness (AOT) is an important parameter for understanding the radiative impact of aerosols. AOT based on lidar measurements is often limited by its finite detection range. In this paper, we have reported a method of fitting and iterative calculation to derive the extinction profile of background aerosols from 0 to 30 km at 532 nm, which is virtually the AOT of the entire atmosphere. The mean extinction derived from this method at the ground level tallies with visibility measurement and it is also consistent with the sun-photometer data, within experimental error. These data have been further treated to study the dust cases. For most of the cases, transmission losses were determined to estimate the extinction as well as lidar ratio. The result of the analysis shows that for background aerosols, a mean lidar ratio of 47±15 sr was found. For dust layers, a mean lidar ratio of 44±19 sr and an optical thickness of 0.53±0.49 were determined at 532 nm. 相似文献