全文获取类型
收费全文 | 115篇 |
免费 | 0篇 |
专业分类
化学 | 17篇 |
力学 | 1篇 |
数学 | 2篇 |
物理学 | 80篇 |
无线电 | 15篇 |
出版年
2022年 | 1篇 |
2018年 | 1篇 |
2014年 | 2篇 |
2013年 | 3篇 |
2012年 | 2篇 |
2011年 | 2篇 |
2010年 | 10篇 |
2009年 | 2篇 |
2008年 | 5篇 |
2007年 | 5篇 |
2006年 | 6篇 |
2005年 | 6篇 |
2004年 | 2篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2000年 | 1篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1996年 | 3篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1961年 | 2篇 |
1960年 | 1篇 |
排序方式: 共有115条查询结果,搜索用时 43 毫秒
21.
Hyland B Svensson CE Ball GC Leslie JR Achtzehn T Albers D Andreoiu C Bricault P Churchman R Cross D Dombsky M Finlay P Garrett PE Geppert C Grinyer GF Hackman G Hanemaayer V Lassen J Lavoie JP Melconian D Morton AC Pearson CJ Pearson MR Phillips AA Schumaker MA Smith MB Towner IS Valiente-Dobón JJ Wendt K Zganjar EF 《Physical review letters》2006,97(10):102501
A high-precision branching ratio measurement for the superallowed beta+ decay of 62Ga was performed at the Isotope Separator and Accelerator radioactive ion beam facility. Nineteen gamma rays emitted following beta+ decay of 62Ga were identified, establishing the dominant superallowed branching ratio to be (99.861+/-0.011)%. Combined with recent half-life and Q-value measurements, this branching ratio yields a superallowed ft value of 3075.6+/-1.4 s for 62Ga decay. These results demonstrate the feasibility of high-precision superallowed branching ratio measurements in the A>or=62 mass region and provide the first stringent tests of the large isospin-symmetry-breaking effects predicted for these decays. 相似文献
22.
K. J. Jalkanen Julian D. Gale P. R. Lassen L. Hemmingsen A. Rodarte I. M. Degtyarenko R. M. Nieminen S. Brøgger Christensen M. Knapp-Mohammady S. Suhai 《Theoretical chemistry accounts》2008,119(1-3):177-190
In this work we present the experimental and theoretical vibrational absorption (VA) and the theoretical vibrational circular
dichroism (VCD) spectra for aframodial. In addition, we present the theoretical VA and VCD spectra for the diasteriomers of
aframodial. Aframodial has four chiral centers and hence has 24 = 16 diasteriomers, which occur in eight pairs of enantiomers. In addition to the four chiral centers, there is an additional
chirality due to the helicity of the entire molecule, which we show by presenting 12 configurations of the 5S,8S,9R,10S enantiomer
of aframodial. The VCD spectra for the diasteriomers and the 12 configurations of one enantiomer are shown to be very sensitive
not only to the local stereochemistry at each chiral center, but in addition, to the helicity of the entire molecule. Here
one must be careful in analyzing the signs of the VCD bands due to the ‘non-chiral’ chromophores in the molecule, since one
has two contributions; one due to the inherent chirality at the four chiral centers, and one due to the chirality of the side
chain groups in specific conformers, that is, its helicity. Theoretical simulations for various levels of theory are compared
to the experimental VA recorded to date. The VCD spectra simulations are presented, but no experimental VCD and Raman spectra
have been reported to date, though some preliminary VCD measurements have been made in Stephens’ lab in Los Angeles. The flexible
side chain is proposed to be responsible for the small size of the VCD spectra of this molecule, even though the chiral part
of the molecule is very rigid and has four chiral centers. In addition to VCD and Raman measurements, Raman optical activity
(ROA) measurements would be very enlightening, as in many cases bands which are weak in both the VA and VCD, may be large
in the Raman and/or ROA spectra. The feasibility of using vibrational spectroscopy to monitor biological structure, function
and activity is a worthy goal, but this work shows that a careful theoretical analysis is also required, if one is to fully
utilize and understand the experimental results. The reliability, reproduceability and uniqueness of the vibrational spectroscopic
experiments and the information which can be gained from them is discussed, as well as the details of the computation of VA,
VCD and Raman (and ROA) spectroscopy for molecules of the complexity of aframodial, which have multiple chiral centers and
flexible side chains.
Festschrift in Honor of Philip J. Stephens’ 65th Birthday. 相似文献
23.
DC Muddiman AP Null JC Hannis 《Rapid communications in mass spectrometry : RCM》1999,13(12):1201-1204
Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
24.
E. J. Prime J. Lassen T. Achtzehn D. Albers P. Bricault T. Cocolios M. Dombsky F. Labrecque J. P. Lavoie M. R. Pearson T. Stubbe N. Lecesne Ch. Geppert K. D. A. Wendt 《Hyperfine Interactions》2006,171(1-3):127-134
The range of isotopes available at the TRIUMF Isotope Separator Accelerator (ISAC) facility has been greatly enhanced by adding
a Resonance Ionization Laser Ion Source (RILIS). A large wavelength range is accessible with the fundamental, second and third
harmonic generation of titanium-sapphire laser light. In addition a dedicated laser is available for non-resonant laser ionization.
The first on-line beam 62Ga was delivered in Dec. 2004. In general RILIS improves the intensity, purity and emittance of ion beams. 62Ga and 26Al and Be beams have been delivered so far on-line.
This work was financed by TRIUMF which is federally funded via a contribution agreement through the National Research Council
of Canada. 相似文献
25.
J. Lassen P. Bricault M. Dombsky J. P. Lavoie Ch. Geppert K. Wendt 《Hyperfine Interactions》2005,162(1-4):69-75
Resonant laser excitation and ionisation is one of the most successful tools for the selective production of radioactive ion beams (RIB) at on-line mass separator facilities. TRIUMF plans to augment the current ion sources with a resonant ionisation laser ion source (RILIS), to use the high production yields from the target, as shown by the delivery of 3*104/s 11Li ions from a standard target ion source with surface ionisation. The development and installation of TRIUMF's RILIS (TRILIS)
is necessary to provide beams of short lived isotopes that conventional ion sources could not produce in sufficient intensity
and purity for nuclear-, and nuclear astrophysics- experiments. A laser system consisting of three tunable titanium–sapphire (TiSa) lasers with frequency doubling and tripling was employed to demonstrate first off-line resonance ionisation
of Ga, and is being installed for first on-line test and a run on 62Ga in December 2004. 相似文献
26.
A dynamical model for multichannel amplification by near-traveling-wave optical amplifiers is presented, and results on crosstalk induced by either amplitude modulation or frequency modulation are given. The mechanisms influencing the crosstalk most are the residual facet reflectivities and the detuning of the channels relative to the amplifier Fabry-Perot spectrum. Calculations of worst-case crosstalk levels are included. The model is verified experimentally for amplitude-modulated signals, and crosstalk levels up to -7 dB are reported. For frequency-modulated signals, estimated crosstalk is significantly lower and can be reduced by high quality facet coatings 相似文献
27.
Saathoff G. Eisenbarth U. Hannemann S. Hoog I. Huber G. Karpuk S. Krohn S. Lassen J. Schwalm D. Weidemüller M. Wolf A. Gwinner G. 《Hyperfine Interactions》2003,146(1-4):71-75
Hyperfine Interactions - The frequency measurement of Doppler-shifted optical lines of ions circulating in a storage ring at high speed permits a sensitive test of the relativistic Doppler-formula... 相似文献
28.
29.
30.
Haines TJ Bionta RM Blewitt G Bratton CB Casper D Claus R Cortez BG Errede S Foster GW Gajewski W Ganezer KS Goldhaber M Jones TW Kielczewska D Kropp WR Learned JG Lehmann E LoSecco JM Matthews J Park HS Price LR Reines F Schultz J Seidel S Shumard E Sinclair D Sobel HW Stone JL Sulak L Svoboda R van der Velde JC Wuest C 《Physical review letters》1986,57(16):1986-1989