全文获取类型
收费全文 | 508篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
化学 | 268篇 |
晶体学 | 10篇 |
力学 | 57篇 |
数学 | 43篇 |
物理学 | 141篇 |
出版年
2020年 | 3篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 19篇 |
2012年 | 23篇 |
2011年 | 24篇 |
2010年 | 14篇 |
2009年 | 8篇 |
2008年 | 18篇 |
2007年 | 26篇 |
2006年 | 31篇 |
2005年 | 22篇 |
2004年 | 14篇 |
2003年 | 9篇 |
2002年 | 16篇 |
2001年 | 9篇 |
2000年 | 19篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 5篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 14篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 8篇 |
1918年 | 2篇 |
1912年 | 2篇 |
1886年 | 3篇 |
1867年 | 2篇 |
排序方式: 共有519条查询结果,搜索用时 31 毫秒
51.
S. Ghosh J. C. R. Hunt J. C. Phillips P. C. H. Miller 《Applied Scientific Research》1993,51(1-2):257-262
This paper presents a study of the fundamental mechanics of droplet and gas motion in sprays. Only vertical sprays are considered and our theoretical analysis identifies two main flow zones, corresponding to where the droplet velocity is much greater than or of the same order as the induced air velocity. Analytical asymptotic results for the induced air velocity for small and large downstream distances confirmed a full numerical calculation and also agreed with experimental results. The second half of the paper deals with some of the most important aspects of spray jets in a cross flow. We find that the ratio of the cross-wind speed to the induced air jet speedU
0/V
j
is a crucial factor for specifying the dynamical behaviour. We present results for an axi-symmetric spray in uniform cross flow for bothweak andstrong cross-winds. 相似文献
52.
The properties of vortical structures at high Reynolds number in uniform flows and near rigid boundaries are reviewed. New
properties are derived by analysing the dynamics of the main flow features and the related integral constraints, including
the relations between mean swirl and bulk speed, the relative level of internal fluctuations to bulk properties, and connections
between the steadiness and topology of the structures. A crucial property that determines energy dissipation and the transport
of inertial particles (with finite fall speed) is the variation across the structure of the ratio of the mean strain rate
(Σ) to the mean vorticity (Ω). It is shown how, once such particles are entrained into the vortical regions of a coherent
structure, they can be transported over significant distances even as the vortices grow and their internal structure is distorted
by internal turbulence, swirling motions and the presence of rigid boundaries. However if the vortex is strongly distorted
by a straining motion so that Σ is greater than Ω, the entrained particles are ejected quite rapidly. These mechanisms are
consistent with previous studies of entrained and sedimenting particles in disperse two phase flows over flat surfaces, and
over bluff obstacles and dunes. They are also tested in more detail here through laboratory observations and measurements
of 50–200-μm particles entrained into circular and non-circular vortices moving first into still air and then onto rigid surfaces placed
parallel and perpendicular to the direction of motion of the vortices. 相似文献
53.
Fern Y. Hunt 《Journal of Dynamics and Differential Equations》2001,13(1):87-105
We present a theoretical basis for a novel way of studying and representing the long-time behavior of finite-dimensional maps. It is based on a finite representation of -pseudo orbits of a map by the sample paths of a suitable Markov chain based on a finite partition of phase space. The use of stationary states of the chain and the corresponding partition elements in approximating the attractors of maps and differential equations was demonstrated in Refs. 7 and 3 and proved for a class of stable attracting sets in Ref. 8. Here we explore the relationship between the communication classes of the Markov chain and basic sets of the Conley decomposition of a dynamical system. We give sufficient conditions for the existence of a chain transitive set and show that basic sets are isolated from each other by neighborhoods associated with closed communication classes of the chain. A partition element approximation of an isolating block is introduced that is easy to express in terms of sample paths. Finally, we show that when the map supports an SBR measure there is a unique closed communication class and the Markov chain restricted to those states is irreducible. 相似文献
54.
Treatment of the labile cluster 1,2-Os3(CO)10(MeCN)2 (1) with the diphosphine ligand 2,3-bis(diphenylphosphino)quinoxaline (dppq) at room temperature affords 1,2-Os3(CO)10(dppq) (2b) as the kinetic product of ligand substitution in 84% yield. 2b isomerizes to the thermodynamically more stable dppq-chelated cluster 1,1-Os3(CO)10(dppq) (2c) as the sole observable product under CO at temperatures below 358 K. The kinetics for the conversion of 2b → 2c have been investigated by NMR spectroscopy in CDCl3 over the temperature range 323-353 K, and the reaction was found to exhibit a rate law that is first order in 2b. The calculated activation parameters [ΔH≠ = 25.4(4) kcal/mol; ΔS≠ = −3(1) eu] support an intramolecular isomerization scenario, one that involves the migration of phosphine and CO groups about the cluster polyhedron. The disposition of the dppq ligand in the isomeric Os3(CO)10(dppq) clusters has been established by X-ray crystallography and 31P NMR spectroscopy. Photolysis of 2c at 366 nm leads to CO loss and ortho metalation of one of the aryl groups on the Ph2P moiety to furnish the hydride cluster HOs3(CO)9[μ-PhP(η1-C6H4)(Ph2P)quinoxaline] (3). The isomerization behavior exhibited by 2b follows that of related diphosphine-substituted Os3 clusters prepared by us. 相似文献
55.
Janz JM Ren Y Looby R Kazmi MA Sachdev P Grunbeck A Haggis L Chinnapen D Lin AY Seibert C McMurry T Carlson KE Muir TW Hunt S Sakmar TP 《Journal of the American Chemical Society》2011,133(40):15878-15881
Cell surface heptahelical G protein-coupled receptors (GPCRs) mediate critical cellular signaling pathways and are important pharmaceutical drug targets. (1) In addition to traditional small-molecule approaches, lipopeptide-based GPCR-derived pepducins have emerged as a new class of pharmaceutical agents. (2, 3) To better understand how pepducins interact with targeted receptors, we developed a cell-based photo-cross-linking approach to study the interaction between the pepducin agonist ATI-2341 and its target receptor, chemokine C-X-C-type receptor 4 (CXCR4). A pepducin analogue, ATI-2766, formed a specific UV-light-dependent cross-link to CXCR4 and to mutants with truncations of the N-terminus, the known chemokine docking site. These results demonstrate that CXCR4 is the direct binding target of ATI-2341 and suggest a new mechanism for allosteric modulation of GPCR activity. Adaptation and application of our findings should prove useful in further understanding pepducin modulation of GPCRs as well as enable new experimental approaches to better understand GPCR signal transduction. 相似文献
56.
An interaction-induced dipole surface (IDS) and a potential energy surface (PES) of collisionally interacting molecular hydrogen pairs H(2)-H(2) was recently obtained using quantum chemical methods (Li, X.; et al. Computational Methods in Science and Engineering, ICCMSE. AIP Conf. Proc. 2009, ; see also Li, X.; et al. Int. J. Spectrosc. 2010, ID 371201). The data account for substantial rotovibrational excitations of the H(2) molecules, as encountered at temperatures of thousands of kelvin (e.g., in the atmospheres of "cool" stars). In this work we use these results to compute the binary collision-induced absorption (CIA) spectra of dense hydrogen gas in the infrared at temperatures up to several thousand kelvin. The principal interest of the work is in the spectra at such higher temperatures, but we also compare our computations with existing laboratory measurements of CIA spectra of dense hydrogen gas and find agreement. 相似文献
57.
Using multireference configuration interaction and coupled-cluster methodologies, with quadruple-ζ basis sets, we explored the potential energy surfaces of the ground and excited states of the neutral and cationic triatomics [Sc,O,H](0,+). In its ground state, the neutral species is trapped into either a linear ScOH or a bent HScO conformation; these two minima are approximately equal in energy and separated by a barrier of 40 kcal/mol. The linear ScOH structure is preferred by the excited states of the neutral species and by all of the electronic states of the charged molecular systems that we studied in this work. Both ScOH and ScOH(+) present ionic characters, Sc(+)OH(-) and Sc(2+)OH(-), similar to those found for the isovalent ScF(0,+) species. The HScO(0,+) structures are obtained by covalent or dative interaction of hydrogen and ScO(0,+). For most of the minima located in this work, we calculated geometries, vibrational frequencies, binding energies, excitation energies, and dipole moments. Our numerical results agree well with existing experimental data. 相似文献
58.
Hans J. Mueller Felix Beckmann David P. Dobson Simon A. Hunt Christian Lathe Nicole Stroncik 《高压研究》2013,33(3):345-354
Here we report recent technical advances that enable viscosity measurements in two DIA-type multi-anvil apparatus with a maximum of 250 tons and 1750 tons. We anticipate that this system will enable viscosity measurements for the pressures up to about 30 GPa. The deformation of the cell assemblies were analyzed by X-ray absorption tomography at beamline W II at DESY/HASYLAB after the high pressure runs. This analysis gave considerable insights into strategies for improving the cell assembly with the result that the optimized assemblies could be used at much higher pressures without blow-outs. We demonstrate using of X-ray transparent cubic boron nitride-anvils (single-stage DIA) and slotted carbide anvils (double-stage DIA) to make the whole melting chamber accessible for the high pressure X-radiography system. Results are demonstrated with viscosity measurements following Stokes’ Law by evaluation of X-radiography sequences taken by a camera equipped with a charge-coupled device sensor (CCD-camera) at pressures of 5 GPa as well as 10 GPa and temperatures of 1890 K. 相似文献
59.
60.
Christopher B. Solnordal Frank R.A. Jorgensen Peter T.L. Koh Arthur Hunt 《Applied Mathematical Modelling》2006
The performance of flash furnace burners can be evaluated quickly and efficiently using CFD modelling. Gas flows are modelled using the conventional Eulerian approach, while Lagrangian particle tracking is used to model the flow of solid feed through the burner and into the reaction shaft. A composite particle model has been developed that considers the solid feed to be made up of single particles containing appropriate quantities of concentrate, flux and dust. Solid fuels (such as coal) can also be included in the composite particle. Reactions between the solids and gas are then modelled using standard heat and mass transfer relationships. Results from the modelling process are shown for BHP-Billiton’s Olympic Dam copper flash smelter with the burner that was used from 1998–2003. Flow patterns, temperature and gas composition distributions, particle dispersion and residence time, and overall extent of sulphur removal are predicted and used to evaluate furnace performance. However, results are sensitive to the assumed size of the composite particles, and plant measurements are required to determine the appropriate composite particle size to predict quantitative data. 相似文献