全文获取类型
收费全文 | 173篇 |
免费 | 5篇 |
专业分类
化学 | 110篇 |
晶体学 | 3篇 |
力学 | 7篇 |
数学 | 7篇 |
物理学 | 51篇 |
出版年
2021年 | 1篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 6篇 |
2012年 | 6篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 10篇 |
2006年 | 14篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2001年 | 11篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有178条查询结果,搜索用时 15 毫秒
1.
Troy N. Eichmann Timothy J. McIntyre Alexis I. Bishop Sosefo Vakata Halina Rubinsztein-Dunlop 《Shock Waves》2007,16(4-5):299-307
Flow visualization experiments were performed for supersonic and hypersonic nitrogen test gas flows over a cylinder. The results
were used to quantify the influence of three-dimensional effects on optical line-of-sight visualization measurements. Images
of cylindrical models of varying aspect ratios (length to diameter) were taken. Shock stand-off distance measurements for
the models were compared with a two-dimensional approximation and numerical simulations. For aspect ratios of two and above,
the two-dimensional approximation was acceptable within experimental uncertainty. The measured shock stand-off decreased by
less than 5% from an asymptotic value for an infinite length cylinder. For smaller aspect ratios, a correction factor for
the shock stand-off needs to be applied if comparisons between the two-dimensional approximation and experimental measurements
are to be drawn. An estimate of this correction factor has been derived from an empirical fit to the available data.
相似文献
2.
Upstream porthole injection in a 2-D scramjet model 总被引:1,自引:0,他引:1
Injection from portholes upstream of the combustion chamber was investigated as a method of delivering fuel into a scramjet.
This method reduces the viscous drag on a model by allowing a reduction in the length of the combustion chamber. At experimental
enthalpies of 3.0 MJ/kg in the T4 shock tunnel, there was no evidence of combustion in the intake, either by shadowgraph or
pressure measurements. Combustion was observed in the combustion chamber. A theoretical extension of these results is made
to a hot wall scenario.
Received 2 January 2001 / Accepted 3 August 2001 相似文献
3.
A computational and experimental study was conducted to assess the potential of testing waverider configurations in a high-performance,
short-duration expansion tube facility. The tests were performed in the newly commissioned X3 superorbital expansion tube
and provide the first experimental data of a waverider tested at a stagnation enthalpy and equivalent flight speed exceeding
40 MJ/kg and 9 km/s, respectively. Two simple caret configurations were chosen as benchmark test cases to test the use of
the facility, instrumentation and numerical models to investigate these flows. The general performance of the sharp and blunt
leading edge waveriders at angles of attack ranging from 0° to 5° were analyzed and compared to CFD and theoretical predictions.
For the conditions tested, the presence of a strong viscous interaction caused the shock wave to be detached from the leading
edge of the models resulting in a significant loss in performance. An analytical model was developed to account for the strong
coupling between the shock wave and boundary layer. Results were shown to be in very good agreement with CFD estimates for
both configurations at all angles of attack considered. Finite-rate chemistry CFD simulations indicated that real gas effects
other than the residual levels of nonequilibrium freestream dissociation present in the expansion tube flow were negligible
for the conditions tested. The study also revealed that a past flow visualization technique gave a false indication of the
leading edge shock location. An improved experimental visualization technique was successfully tested with results from these
tests correlating well with computational estimates. This study successfully demonstrated the use of the facility to study
waverider performance at speeds representative of orbital flight.
相似文献
4.
5.
Sally M. McIntyre Jill Wisnewski Ferguson R.S. Houk 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(8):581-587
The method of comparing experimental and calculated ion ratios to determine a gas kinetic temperature (Tgas) characteristic of the origin of a polyatomic ion in inductively coupled plasma-mass spectrometry (ICP-MS) is applied to ArO+. Repeated measurements of ion ratios involving this species yield erratic Tgas values. Complications arise from the predicted presence of a low-lying excited electronic state (2Π) above the 4Σ ground state. Omission of this excited state yields unreasonably high temperatures (> 10,000 K) for nine out of nineteen trials. Inclusion of the excited electronic state in the partition function of ArO+ causes temperatures to increase further. The problem appears to be related to the prediction that ArO+ in the 2Π excited state dissociates into Ar+ and O, different products than ArO+ 4Σ which dissociates into Ar and O+. Adjustments to the calculations to account for these different products yield reasonable temperatures (2100 to 3500 K) that are consistent from day-to-day and similar to those seen for other weakly-bound polyatomic ions. 相似文献
6.
Anna S. Gardberg Brian S. Potter Rex A. Palmer Garry J. McIntyre Dean A. A. Myles 《Journal of chemical crystallography》2011,41(4):470-480
Abstract
Single-crystal neutron diffraction data were collected at 20 K to a resolution of 1.05 ? on a crystal of the inverse formyl peptide receptor agonist cyclosporin H, CsH, (crystal form II, CsH-II) on the Laue diffractometer VIVALDI at the Institut Laue-Langevin (Grenoble). The solvent structure and hydrogen bonding network of CsH-II have been unambiguously determined by single-crystal neutron diffraction; the agreement factor R(F 2) is 13.5% for all 2726 reflections. All hydrogen atom positions, including methyl-group orientations, have been determined by crystallographic refinement. The neutron structure of cyclosporin provides unique and complementary insights into methyl orientation, hydrogen-bonding, and solvent interactions that are not available from X-ray analysis alone. 相似文献7.
P. L. Reeder T. W. Bowyer J. I. McIntyre W. K. Pitts 《Journal of Radioanalytical and Nuclear Chemistry》2001,248(3):617-622
The International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty will include measurements of Xe fission products. Pacific Northwest National Laboratory has developed an automated system for separating Xe from air which detects Xe fission products using a beta-gamma counting system for 131mXe, 133mXe, 133gXe, and 135gXe. Betas and conversion electrons are detected in a plastic scintillation cell containing the Xe sample. Gamma and X-rays are detected in a NaI(Tl) scintillation detector which surrounds the plastic scintillator sample cell. Two-dimensional pulse-height spectra of gamma-energy versus beta-energy are obtained. The plastic scintillator spectrum in coincidence with the 31-keV X-rays from 131mXe. 133mXe, and 133gXe is a complex mixture of conversion electrons and betas. A new technique to simultaneously measure the delayed coincidence (T
1/2 = 6.27 ns) between beta-particles from 133gXe and conversion electrons depopulating the 81-keV state in 133 Cs is being developed. This technique allows separation of the 133gXe beta spectrum from the conversion electrons due to 131mXe and 133mXe and uniquely quantifies all three nuclides. 相似文献
8.
The tropolone subunit of the naturally occurring alkaloid rubrolone aglycon is synthesized via a short reaction sequence starting with a 1,3-dipolar cycloaddition of a pyrylium ylide and indenone, followed by enone oxidation, oxygen-bridge elimination and finally hydroxy group oxidation. 相似文献
9.
Jimmy Yuk Kristina L. McIntyre Christian Fischer Joshua Hicks Kimberly L. Colson Ed Lui Dan Brown John T. Arnason 《Analytical and bioanalytical chemistry》2013,405(13):4499-4509
The use of 1H-NMR-based metabolomics to distinguish and identify unique markers of five Ontario ginseng (Panax quinquefolius L.) landraces and two ginseng species (P. quinquefolius and P. ginseng) was evaluated. Three landraces (2, 3, and 5) were distinguished from one another in the principal component analysis (PCA) scores plot. Further analysis was conducted and specific discriminating metabolites from the PCA loadings were determined. Landraces 3 and 5 were distinguishable on the basis of a decreased NMR intensity in the methyl ginsenoside region, indicating decreased overall ginsenoside levels. In addition, landrace 5 was separated by an increased amount of sucrose relative to the rest of the landraces. Landrace 2 was separated from the rest of the landraces by the increased level of ginsenoside Rb1. The Ontario P. quinquefolius was also compared with Asian P. ginseng by PCA, and clear separation between the two groups was detected in the PCA scores plot. The PCA loadings plot and a t-test NMR difference plot were able to identify an increased level of maltose and a decreased level of sucrose in the Asian ginseng compared with the Ontario ginseng. An overall decrease of ginsenoside content, especially ginsenoside Rb1, was also detected in the Asian ginseng’s metabolic profile. This study demonstrates the potential of NMR-based metabolomics as a powerful high-throughput technique in distinguishing various closely related ginseng landraces and its ability to identify metabolic differences from Ontario and Asian ginseng. The results from this study will allow better understanding for quality assessment, species authentication, and the potential for developing a fully automated method for quality control. Figure
Principal component analysis scores and loadings plot for differentiating between closely-related ginseng landraces in Ontario, Canada 相似文献
10.
Deshmukh Nikhil Prinke Amanda Miller Brian McIntyre Justin 《Journal of Radioanalytical and Nuclear Chemistry》2017,311(3):1849-1857
The aim of this paper is to compare radioxenon beta–gamma analysis algorithms using simulated spectra with experimentally measured background, where the ground truth of the signal is known. We believe that this is among the largest efforts to date in terms of the number of synthetic spectra generated and number of algorithms compared using identical spectra. We generate an estimate for the minimum detectable counts for each isotope using each algorithm. The paper also points out a conceptual model to put the various algorithms into a continuum. Our results show that existing algorithms can be improved and some newer algorithms can be better than the ones currently used.
相似文献