全文获取类型
收费全文 | 956篇 |
免费 | 22篇 |
国内免费 | 18篇 |
专业分类
化学 | 449篇 |
晶体学 | 21篇 |
力学 | 25篇 |
数学 | 253篇 |
物理学 | 248篇 |
出版年
2022年 | 9篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 21篇 |
2015年 | 16篇 |
2014年 | 17篇 |
2013年 | 37篇 |
2012年 | 39篇 |
2011年 | 47篇 |
2010年 | 24篇 |
2009年 | 30篇 |
2008年 | 34篇 |
2007年 | 42篇 |
2006年 | 31篇 |
2005年 | 33篇 |
2004年 | 23篇 |
2003年 | 31篇 |
2002年 | 34篇 |
2001年 | 32篇 |
2000年 | 13篇 |
1999年 | 18篇 |
1998年 | 14篇 |
1997年 | 16篇 |
1996年 | 21篇 |
1995年 | 13篇 |
1994年 | 27篇 |
1993年 | 18篇 |
1992年 | 15篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 18篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 11篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 19篇 |
1980年 | 10篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 6篇 |
1976年 | 12篇 |
1975年 | 10篇 |
1974年 | 13篇 |
1973年 | 17篇 |
1972年 | 9篇 |
1969年 | 6篇 |
排序方式: 共有996条查询结果,搜索用时 31 毫秒
41.
This paper describes the development of a lattice Boltzmann (LB) model for a binary gas mixture, and applications to channel flow driven by a density gradient with diffusion slip occurring at the wall. LB methods for single component gases typically use a non‐physical equation of state in which the relationship between pressure and density varies according to the scaling used. This is fundamentally unsuitable for extension to multi‐component systems containing gases of differing molecular masses. Substantial variations in the species densities and pressures may exist even at low Mach numbers; hence, the usual linearized equation of state for small fluctuations is unsuitable. Also, existing methods for implementing boundary conditions do not extend easily to novel boundary conditions, such as diffusion slip. The new model developed for multi‐component gases avoids the pitfalls of some other LB models. A single computational grid is shared by all the species, and the diffusivity is independent of the viscosity. The Navier–Stokes equation for the mixture and the Stefan–Maxwell diffusion equation are both recovered by the model. Diffusion slip, the non‐zero velocity of a gas mixture at a wall parallel to a concentration gradient, is successfully modelled and validated against a simple one‐dimensional model for channel flow. To increase the accuracy of the scheme, a second‐order numerical implementation is needed. This may be achieved using a variable transformation method that does not increase the computational time. Simulations were carried out on hydrogen and water diffusion through a narrow channel for varying total pressure and concentration gradients. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
42.
The OPAL research reactor in Australia has been used to determine k 0 values for 134mCs, 134Cs, 192Ir and 194Ir. Values for 24Na have also been measured for quality control. The neutron flux at the irradiation positions was very highly thermalised (f > 2,000), resulting in almost negligible activation by epithermal neutrons. As a consequence, the contribution to the total uncertainty of the k 0 values from epithermal-related factors such as Q 0 and $ \bar{E}_{\text{r}} $ was very small. The measured caesium k 0 values have been compared with the library values as well as with recent measurements by St Pierre et al. and Farina Arboccò et al. While there are k 0 values for 194Ir in the library, no 192Ir values have been measured previously. Despite 192Ir having a higher sensitivity than 194Ir, k 0 values were not measured during the establishment of the k 0-method because the nuclear data available at the time indicated that the activation cross-section of 191Ir deviated significantly from 1/v behaviour (g(T n ) ≠ 1), which would result in unacceptable errors if k 0 analysis were to be carried out using the Høgdahl convention. However later nuclear data compilations showed that 191Ir has better 1/v behaviour than previously reported, making it suitable for k 0 analysis using the Høgdahl convention. For completeness, k 0 values have been determined using both the Høgdahl and modified-Westcott conventions and these have been compared with library (194Ir) and calculated values. 相似文献
43.
Adare A Afanasiev S Aidala C Ajitanand NN Akiba Y Al-Bataineh H Alexander J Al-Jamel A Aoki K Aphecetche L Armendariz R Aronson SH Asai J Atomssa ET Averbeck R Awes TC Azmoun B Babintsev V Baksay G Baksay L Baldisseri A Barish KN Barnes PD Bassalleck B Bathe S Batsouli S Baublis V Bauer F Bazilevsky A Belikov S Bennett R Berdnikov Y Bickley AA Bjorndal MT Boissevain JG Borel H Boyle K Brooks ML Brown DS Bucher D Buesching H Bumazhnov V Bunce G Burward-Hoy JM Butsyk S Campbell S Chai JS Chang BS 《Physical review letters》2007,98(16):162301
Differential measurements of elliptic flow (v2) for Au+Au and Cu+Cu collisions at sqrt[sNN]=200 GeV are used to test and validate predictions from perfect fluid hydrodynamics for scaling of v2 with eccentricity, system size, and transverse kinetic energy (KE T). For KE T identical with mT-m up to approximately 1 GeV the scaling is compatible with hydrodynamic expansion of a thermalized fluid. For large values of KE T mesons and baryons scale separately. Quark number scaling reveals a universal scaling of v2 for both mesons and baryons over the full KE T range for Au+Au. For Au+Au and Cu+Cu the scaling is more pronounced in terms of KE T, rather than transverse momentum. 相似文献
44.
Poly(ethylene glycol) (PEG) hydrogels have been used to encapsulate fluorescently labeled molecules in order to detect a variety
of analytes. The hydrogels are designed with a mesh size that will retain the sensing elements while allowing for efficient
diffusion of small analytes. Some sensing assays, however, require a conformational change or binding of large macromolecules,
which may be sterically prohibited in a dense polymer matrix. A process of hydrogel microporation has been developed to create
cavities within PEG microspheres to contain the assay components in solution. This arrangement provides improved motility
for large sensing elements, while limiting leaching and increasing sensor lifetime. Three hydrogel compositions, 100% PEG,
50% PEG, and microporated 100% PEG, were used to create pH-sensitive microspheres that were tested for response time and stability.
In order to assess motility, a second, more complex sensor, namely a FITC-dextran/TRITC-Con A glucose-specific assay was encapsulated
within the microspheres. 相似文献
45.
46.
A gelatin matrix was simultaneously doped with nine equimolar, homologous, tetraalkylammonium salts ranging in mass from 210 to 700 Da. Bombardment of the sample with kiloelectronvolt ions resulted in a nonidentical distribution of relative cation intensities with a maximum at m/z 242 for samples with a total salt concentration of 0.004 g of salt/g of gelatin. A rapid increase in relative intensities with increasing mass is observed for the low mass salts and is believed to be linked to changes in the ionization efficiencies. The changes in ionization efficiencies are likely related to decreasing coulombic attractive forces between the organic cation and the counterion. Disappearance cross-sections, determined from decay curves, indicate that sputter-induced damage increases with increasing mass of the cation. Fragment-to-intact cation ratios also suggest that damage accumulates fastest in the heaviest salts. These observations indicate that desorption yields of the organic salts in a gelatin matrix decrease with increasing mass. In addition, suppression of lower mass tetraalkylammonium salt intact cation intensities was observed for salt-in-gelatin concentrations greater than 10−3 g/g. 相似文献
47.
Yuhua Huang Frank Bennett Vishal Verma F. George Njoroge Malcolm MacCoss 《Tetrahedron letters》2012,53(26):3203-3205
A direct conversion of a thiolacetate to its corresponding sulfonyl chloride in the presence of acid and base sensitive functional groups is described. 相似文献
48.
Bennett N. Walker Jessica A. Stolee Deanna L. Pickel Scott T. Retterer Akos Vertes 《Applied Physics A: Materials Science & Processing》2010,101(3):539-544
Experimental assessment of the thermal load induced by fast laser pulses on micro- and nanostructures through IR imaging is
currently too slow and lacks the spatial resolution to be useful. In this paper, we introduce a method based on measuring
the laser-induced yields of ions to compare the thermal loads on nanofabricated silicon structures, when exposed to nanosecond
laser pulses. The laser fluences at which the ion yields of, for example, sodiated and potassiated peptides ions are equal
for two different structures correspond to equivalent thermal loads. Using alkalinated peptides is a convenient choice because
the corresponding ion intensities are easily measured up to the melting point of silicon. As an example, we compare the nanosecond
laser heating of silicon nanopost arrays with diverse post diameters and periodicities. Assessment of the thermal load through
ion yield measurements can also be used to verify model assumptions for heat transport regimes in nanostructures. 相似文献
49.
Jonathan M. Bennett 《Transactions of the American Mathematical Society》2002,354(12):4871-4892
We study certain Hilbert transforms and maximal functions along variable flat curves in the plane. We obtain their boundedness by considering the oscillatory singular integrals which arise from an application of a partial Fourier transform.
50.
Band gaps and defect modes in periodically structured waveguides 总被引:2,自引:0,他引:2
Munday JN Bennett CB Robertson WM 《The Journal of the Acoustical Society of America》2002,112(4):1353-1358
This work examines a simple one-dimensional acoustic band gap system made from a diameter-modulated waveguide. Experimental and theoretical results are presented on perfectly periodic waveguide arrays showing the presence of band gaps--frequency intervals in which the transmission of sound is forbidden. The introduction of defects in the perfect periodicity leads to narrow frequency transmission bands--defect states--within the forbidden band gaps. The circular cross-section waveguide system is straightforward to simulate theoretically and experimental results demonstrate good agreement with theory. The experimental transmission of the periodic waveguide arrays is measured using an impulse response technique. 相似文献