全文获取类型
收费全文 | 254篇 |
免费 | 4篇 |
专业分类
化学 | 127篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 10篇 |
物理学 | 116篇 |
出版年
2020年 | 4篇 |
2016年 | 3篇 |
2013年 | 15篇 |
2012年 | 6篇 |
2011年 | 10篇 |
2010年 | 9篇 |
2009年 | 4篇 |
2008年 | 6篇 |
2007年 | 12篇 |
2006年 | 7篇 |
2005年 | 4篇 |
2004年 | 7篇 |
2003年 | 3篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 14篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1968年 | 2篇 |
1939年 | 3篇 |
1933年 | 2篇 |
1930年 | 2篇 |
1914年 | 2篇 |
1905年 | 2篇 |
1892年 | 2篇 |
1888年 | 2篇 |
1883年 | 2篇 |
1876年 | 2篇 |
排序方式: 共有258条查询结果,搜索用时 47 毫秒
91.
Chuen Y. Poon Julie M. Edwards C. John Evans Ashley D. Harris Beverly Tsai-Goodman Charlotte E. Bolton John R. Cockcroft Richard G. Wise Sailesh Kotecha 《Magnetic resonance imaging》2013
Purpose
To assess the feasibility of measuring pulmonary artery (PA) pulse wave velocity (PWV) in children breathing ambient air and 12% oxygen.Methods
Velocity-encoded phase-contrast MR images of the PA were acquired in 15 children, aged 9–12 years, without evidence of cardiac or pulmonary diseases. PWV was derived as the ratio of flow to area changes during early systole. Each child was scanned twice, in air and after at least 20 minutes into inspiratory hypoxic challenge. Intra-observer and inter-observer variability and repeatability were also compared.Results
PA PWV, which was successfully measured in all subjects, increased from 1.31 ± 0.32 m/s in air to 1.61 ± 0.58 m/s under hypoxic challenge (p = 0.03). Intra- and inter-observer coefficients of variations were 9.0% and 15.6% respectively. Good correlation within and between observers of r = 0.92 and r = 0.72 respectively was noted for PA PWV measurements. Mean (95% limit of agreement) intra- and inter-observer agreement on Bland–Altman analysis were − 0.02 m/s (− 0.41–0.38 m/s) and -0.28 m/s (− 1.06–0.49 m/s).Conclusion
PA PWV measurement in children using velocity-encoded MRI is feasible, reproducible and sufficiently sensitive to detect differences in PA compliance between normoxia and hypoxia. This technique can be used to detect early changes of PA compliance and monitor PAH in children. 相似文献92.
A. Ya. Faenov T. A. Pikuz Y. Fukuda M. Kando H. Kotaki T. Homma K. Kawase T. Kameshima A. Pirozhkov A. Yogo M. Tampo M. Mori H. Sakaki I. Hayashi T. Nakamura S. A. Pikuz Jr. V. Kartashev I. Yu. Skobelev A. Giulietti C. A. Checchetti A. S. Boldarev V. A. Gasilov A. I. Magunov S. Kar M. Borghesi P. Bolton H. Daido T. Tajima I. Kato S. V. Bulanov 《JETP Letters》2009,89(10):485-491
It has been shown that a femtosecond plasma of cluster targets is an almost isotropic source of fast ions and, hence, can be used to obtain ionographic images with a wide field of view. The spatial resolution of the resulting ionographic images is no worse than 600 nm, which corresponds to a uniquely high value of about 105 of the ratio of the field of view to the resolution. The use of 100–300-keV ion fluxes ensures the sensitivity of the method to the sample thickness of no worse than 100 nm even for samples consisting of light chemical elements (C, H). The proposed method can be used to obtain images of low-contrast biological objects, thin films, membranes, and other nanostructured objects. 相似文献
93.
M. Suzuki H. Kiriyama I. Daito H. Okada Y. Nakai S. Orimo M. Sato Y. Tamaoki T. Yoshii J. Maeda S. Matsuoka H. Kan P. R. Bolton H. Daido S. Kawanishi 《Applied physics. B, Lasers and optics》2009,97(2):379-382
We report the highest energy broadband laser pulses at a center wavelength of 1030 nm based on optical parametric chirped-pulse amplification (OPCPA). We have demonstrated amplification of 1030 nm femtosecond laser pulses from a broadband Yb oscillator to over 6.5 mJ with a total gain of greater than 107 achieved in a single pass through only 56 mm of gain material at a 10 Hz repetition rate. The amplified spectral bandwidth of 10.8 nm affords recompression to a 230 fs pulse duration following amplification. As an alternative to the regenerative amplifier (RA) this system is one of the more promising candidates for realizing compact, high intensity, direct diode-pumped, high repetition rate femtosecond Yb:YAG chirped-pulse amplification (CPA) in laser systems. 相似文献
94.
Nakul Rampal Abdulmalik Ajenifuja Andi Tao Christopher Balzer Matthew S. Cummings Arwyn Evans Rocio Bueno-Perez David J. Law Leslie W. Bolton Camille Petit Flor Siperstein Martin P. Attfield Megan Jobson Peyman Z. Moghadam David Fairen-Jimenez 《Chemical science》2021,12(36):12068
The separation of CO/N2 mixtures is a challenging problem in the petrochemical sector due to the very similar physical properties of these two molecules, such as size, molecular weight and boiling point. To solve this and other challenging gas separations, one requires a holistic approach. The complexity of a screening exercise for adsorption-based separations arises from the multitude of existing porous materials, including metal–organic frameworks. Besides, the multivariate nature of the performance criteria that needs to be considered when designing an optimal adsorbent and a separation process – i.e. an optimal material requires fulfillment of several criteria simultaneously – makes the screening challenging. To address this, we have developed a multi-scale approach combining high-throughput molecular simulation screening, data mining and advanced visualization, as well as process system modelling, backed up by experimental validation. We have applied our recent advances in the engineering of porous materials'' morphology to develop advanced monolithic structures. These conformed, shaped monoliths can be used readily in industrial applications, bringing a valuable strategy for the development of advanced materials. This toolbox is flexible enough to be applied to multiple adsorption-based gas separation applications.The separation of challenging mixtures through adsorption is a multidimensional problem that requires a holistic approach. Our toolbox combines experiments, molecular and process simulations with data visualization to find optimal, porous materials. 相似文献
95.
Harutyunyan AR Awasthi N Jiang A Setyawan W Mora E Tokune T Bolton K Curtarolo S 《Physical review letters》2008,100(19):195502
Fe nanoclusters are becoming the standard catalysts for growing single-walled carbon nanotubes via chemical vapor decomposition. Contrary to the Gibbs-Thompson model, we find that the reduction of the catalyst size requires an increase of the minimum temperature necessary for the growth. We address this phenomenon in terms of solubility of C in Fe nanoclusters and, by using first-principles calculations, we devise a simple model to predict the behavior of the phases competing for stability in Fe-C nanoclusters at low temperature. We show that, as a function of particle size, there are three scenarios compatible with steady state growth, limited growth, and no growth of single-walled carbon nanotubes, corresponding to unaffected, reduced, and no solubility of C in the particles. 相似文献
96.
Viel M Becker GD Bolton JS Haehnelt MG Rauch M Sargent WL 《Physical review letters》2008,100(4):041304
We present constraints on the mass of warm dark matter (WDM) particles derived from the Lyman-alpha flux power spectrum of 55 high-resolution HIRES spectra at 2.0 or approximately 1.2 keV (2sigma) if the WDM consists of early decoupled thermal relics and m(WDM) > or approximately 5.6 keV (2sigma) for sterile neutrinos. Adding the Sloan Digital Sky Survey Lyman-alpha flux power spectrum, we get m(WDM) > or approximately 4 keV and m(WDM) > or approximately 28 keV (2sigma) for thermal relics and sterile neutrinos. These results improve previous constraints by a factor of 2. 相似文献
97.
A molecular‐level computational study of the diffusion and solubility of water and oxygen in carbonaceous polyethylene nanocomposites 下载免费PDF全文
Edvin Erdtman Martin Bohlén Peter Ahlström Thomas Gkourmpis Mikael Berlin Thorbjörn Andersson Kim Bolton 《Journal of Polymer Science.Polymer Physics》2016,54(5):589-602
Monte Carlo and molecular dynamics simulations were performed to investigate the effect on the solubility, diffusion, and permeability of water and oxygen when adding graphene or single‐walled carbon nanotubes (SWCNTs) to polyethylene (PE). When compared with pure PE, addition of graphene lowered the solubility of water, whereas at lower temperatures, the oxygen solubility increased because of the oxygen–graphene interaction. Addition of SWCNTs lowered the solubility of both water and oxygen when compared with pure PE. A detailed analysis showed that an ordered structure of PE is induced near the additive surface, which leads to a decrease in the diffusion coefficient of both penetrants in this region. The addition of graphene does not change the permeation coefficient of oxygen (in the direction parallel to the filler) and, in fact, may even increase this coefficient when compared with pure PE. In contrast, the water permeability is decreased when graphene is added to PE. The addition of SWCNTs decreases the permeability of both penetrants. Graphene can consequently be added to selectively increase the solubility and permeation of oxygen over water, at least at lower temperatures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 589–602 相似文献
98.
99.
100.
The syntheses of two side chain liquid crystal polymers, a polyacrylate and a polymethacrylate, are reported. In each of the polymers the liquid-crystalline side group carries an asymmetric carbon atom, thereby making some of the liquid crystal phases formed by the polymers optically active and chiral. For the chiral polyacrylate smectic A and chiral ferroelectric smectic C phases are observed, however for the chiral polymethacrylate a cholesteric phase is detected above the smectic A phase. It is found that the smectic A to cholesteric phase transition is mediated by the formation of an intermediary twisted smectic A phase. This intermediary phase is a liquid-crystalline analogue of the Abrikosov flux phase found in Type II superconductors. 相似文献