全文获取类型
收费全文 | 438篇 |
免费 | 7篇 |
国内免费 | 4篇 |
专业分类
化学 | 232篇 |
晶体学 | 10篇 |
力学 | 19篇 |
数学 | 23篇 |
物理学 | 165篇 |
出版年
2021年 | 3篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 10篇 |
2013年 | 13篇 |
2012年 | 8篇 |
2011年 | 16篇 |
2010年 | 11篇 |
2009年 | 6篇 |
2008年 | 12篇 |
2007年 | 24篇 |
2006年 | 25篇 |
2005年 | 13篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 15篇 |
2001年 | 10篇 |
2000年 | 19篇 |
1998年 | 4篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 19篇 |
1992年 | 18篇 |
1991年 | 6篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1968年 | 4篇 |
1938年 | 2篇 |
1936年 | 2篇 |
1934年 | 3篇 |
1933年 | 2篇 |
1929年 | 2篇 |
1927年 | 2篇 |
1917年 | 4篇 |
1890年 | 2篇 |
1889年 | 2篇 |
1885年 | 2篇 |
排序方式: 共有449条查询结果,搜索用时 93 毫秒
421.
V. N. Fedosseev B. A. Marsh D. V. Fedorov U. Köster E. Tengborn 《Hyperfine Interactions》2005,162(1-4):15-27
The resonance ionization laser ion source (RILIS) of the ISOLDE on-line isotope separation facility is based on the method
of laser step-wise resonance ionization of atoms in a hot metal cavity. The atomic selectivity of the RILIS complements the
mass selection process of the ISOLDE separator magnets to provide beams of a chosen isotope with greatly reduced isobaric
contamination. Using a system of dye lasers pumped by copper vapour lasers, ion beams of 24 elements have been generated at
ISOLDE with ionization efficiencies in the range of 0.5–15%. As part of the ongoing RILIS development off-line resonance ionization
spectroscopy studies carried out in 2003 and 2004 have determined the optimal three-step ionization schemes for scandium,
antimony, dysprosium and yttrium. 相似文献
422.
Aslak Bakke Buan Robert J. Marsh Idun Reiten Gordana Todorov with an Appendix coauthored in addition by P. Caldero B. Keller 《Proceedings of the American Mathematical Society》2007,135(10):3049-3060
Cluster algebras are commutative algebras that were introduced by Fomin and Zelevinsky in order to model the dual canonical basis of a quantum group and total positivity in algebraic groups. Cluster categories were introduced as a representation-theoretic model for cluster algebras. In this article we use this representation-theoretic approach to prove a conjecture of Fomin and Zelevinsky, that for cluster algebras with no coefficients associated to quivers with no oriented cycles, a seed is determined by its cluster. We also obtain an interpretation of the monomial in the denominator of a non-polynomial cluster variable in terms of the composition factors of an indecomposable exceptional module over an associated hereditary algebra.
423.
J. Sauvage J. Genevey B. Roussière S. Franchoo A. N. Andreyev N. Barré J. -F. Clavelin H. De Witte D. V. Fedorov V. N. Fedoseyev L. M. Fraile X. Grave G. Huber M. Huyse H. B. Jeppesen U. K?ster P. Kunz S. R. Lesher B. A. Marsh I. Mukha J. Oms M. Seliverstov I. Stefanescu K. Van de Vel J. Van de Walle P. Van Duppen Yu. M. Volkov 《The European Physical Journal A - Hadrons and Nuclei》2009,39(1):33-48
The /EC decay of 189m, gPb has been studied at the ISOLDE facility using nuclear spectroscopy and in-source laser spectroscopy. A level scheme of
189Tl has been built from - coincidence relationships and information on the feeding of some excited levels of 189Tl provided by the hyperfine spectra obtained from laser ionization. The half-lives of both the 13/2+ and 3/2-
189Pb isomers have been estimated to be T
1/2 = 50±3 s and T
1/2 = 39±8 s, respectively. Calculations have been performed for different oblate and prolate nuclear deformations using an axial-rotor
coupled to one-quasiparticle model, a structure has been suggested for the low-lying levels of the 189Tl nucleus. 相似文献
424.
Najmudin Z. Dangor A.E. Modena A. Salvati M.R. Clayton C.E. Danson C.N. Gordon D. Joshi C.J. Marsh K.A. Malka V. Muggli P. Neely D. Walsh F.N. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2000,28(4):1057-1070
The interaction of an intense short pulse laser (>5×10 18 Wcm-2) with underdense plasma was extensively studied. The beam is found to be highly susceptible to the forward Raman scattering instability. At sufficiently high growth rates, this can lead to wavebreaking with the resultant production of a high flux of accelerated electrons (>1011 for E>2 MeV). Some electrons are found to be accelerated well above the dephasing energy, up to 94 MeV. Self-scattered images intimate the presence of high-intensity channels that extend more than 3.5 mm or 12 Rayleigh lengths. These filaments do not follow the axis of laser propagation, but are seen to be emitted within an f4 cone centered around this axis. Spectra of the self-scattered light show that the main contribution of the scattering is not from light captured within these filaments. But there is evidence for self-phase modulation from effects such as ionization and relativistic self-focusing. However, no clear correlation is observed between channel length and the number or energies of accelerated electrons. Evidence for high intensities within the channels is given by small-angle Thomson scattering of the plasma wave generated therein, with this method, the intensity is found to be of the order of 1018 Wcm-2 greater than 12 Rayleigh lengths from focus 相似文献
425.
Muggli P. Marsh K.A. Wang S. Clayton C.E. Lee S. Katsouleas T.C. Joshi C. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1999,27(3):791-799
A photo-ionized lithium source is developed for plasma acceleration applications. A homogeneous column of lithium neutral vapor with a density of 2×1015-3 is confined by helium gas in a heat-pipe oven. A UV laser pulse ionizes the vapor. In this device, the length of the neutral vapor and plasma column is 25 cm. The plasma density was measured by laser interferometry in the visible on the lithium neutrals and by CO2 laser interferometry on the plasma electrons. The maximum measured plasma density was 2.9×10 14 cm-3, limited by the available UV fluence (≈83 mJ/cm2), corresponding to a 15% ionization fraction. After ionization, the plasma density decreases by a factor of two in about 12 μs. These results show that such a plasma source is scaleable to lengths of the order of 1 m and should satisfy all the requirements for demonstrating the acceleration of electrons by 1 GeV in a 1-GeV/m amplitude plasma wake 相似文献
426.
Brandenburg G Ershov A Kim DY Wilson R Benslama K Eisenstein BI Ernst J Gollin GD Hans RM Karliner I Lowrey N Marsh MA Plager C Sedlack C Selen M Thaler JJ Williams J Edwards KW Ammar R Besson D Zhao X Anderson S Frolov VV Kubota Y Lee SJ Li SZ Poling R Smith A Stepaniak CJ Urheim J Ahmed S Alam MS Jian L Saleem M Wappler F Eckhart E Gan KK Gwon C Hart T Honscheid K Hufnagel D Kagan H Kass R Pedlar TK Thayer JB Von Toerne E Wilksen T Zoeller MM Richichi SJ Severini H Skubic P Dytman SA Nam S 《Physical review letters》2002,89(22):222001
Using 13.53 fb(-1) of CLEO data, we have measured the ratios of the branching fractions R(+)(e),R(+)(mu) and the combined branching fraction ratio R(+)(l), defined by R(+)(l)=[B(D+-->K(*0)l(+)nu(l))]/[B(D+-->K-pi(+)pi(+))]. We find R(+)(e)=0.74+/-0.04+/-0.05, R(+)(mu)=0.72+/-0.10+/-0.05, and R(+)(l)=0.74+/-0.04+/-0.05, where the first and second errors are statistical and systematic, respectively. The known branching fraction B(D+-->K-pi(+)pi(+)) leads to B(D+-->K(*0)e(+)nu(e))=(6.7+/-0.4+/-0.5+/-0.4)%, B(D+-->K(*0)mu(+)nu(mu))=(6.5+/-0.9+/-0.5+/-0.4)%, and B(D+-->K(*0)l(+)nu(l))=(6.7+/-0.4+/-0.5+/-0.4)%, where the third error is due to the uncertainty in B(D+-->K-pi(+)pi(+)). 相似文献
427.
[reaction: see text] 5,5,5,5',5',5'-Hexafluoroleucine (6), a fluorous analogue of leucine, is of considerable interest as a building block in the design of fluorous proteins and peptides. We report a short and efficient synthesis of 6, which is obtained from N-Cbz-L-serine (1) in 50% overall yield, 99% enantiomeric excess, and in multigram quantities. Key steps are addition of a serine-derived organozincate to hexafluoroacetone to construct the hexafluoroleucine side chain, followed by radical-mediated deoxygenation of the resulting tertiary alcohol. 相似文献
428.
A. Bodek R. Breedon R.N. Coleman W. Marsh S. Olsen J.L. Ritchie B.C. Barish R.L. Messner M.H. Shaevitz E.J. Siskind F.S. Merritt H.E. Fisk Y. Fukushima P.A. Rapidis G. Donaldson S.G. Wojcicki 《Physics letters. [Part B]》1982,113(1):82-86
The rates for same-sign and opposite-sign dimuon events with missing energy (indicative of final-state neutrinos) have been measured in 278 GeV π?-Fe and 350 GeV proton-Fe collisions. The main source of opposite-sign events is two semi-leptonic decays of hadronically produced charm states. The same-sign events are consistent with background from pion and kaon decays. We obtain a limit of 0.044 (90% CL) on the fraction of D0 semileptonic decays that result in the wrong-sign muon and conclude that less than 9% (90% CL) of same-sign dimuon events produced in neutrino interactions can be attributed to D0-0 mixing. The data imply δm < 6.5 × 10?4 eV and for the difference in mass and inverse lifetime of the CP eigenstates of the D0. Limits on diffractive bottom production cross sections in proton and pion collisions are also presented. 相似文献
429.
Polyamines stabilise nucleic acids against chemical and enzymatic degradation, facilitate the formation of secondary and tertiary structures and enhance cellular uptake. Therefore methods for the syntheses of polyamine-nucleic acid conjugates are of interest. A route for the syntheses of RNA-spermine conjugates has been developed. The polyamine was introduced to the C-5 position of uridine via an ethyl tether and the molecule elaborated into a synthon suitable for oligoribonucleotide assembly. The resultant oligomers were components of the hairpin ribozyme. Characterisation of the spermine-conjugated catalytic RNA revealed that attachment of the polyamine was well tolerated in three of four positions, namely U41, U37 and U34, suggesting that conjugation to C-5 brings about minimal structural perturbation. 相似文献
430.
Lee KH Matzapetakis M Mitra S Marsh EN Pecoraro VL 《Journal of the American Chemical Society》2004,126(30):9178-9179
Substitution of an alanine for leucine (shown in light blue) in the hydrophobic interior of designed three-stranded coiled coils allows for the control of metal ion coordination number and geometry. The influence of this perturbation by a noncoordinating residue can be monitored by the dramatic impact on the 113Cd NMR spectrum. The structural effect occurs even when the residue substitution is as much as 7 A from the metal binding site. 相似文献