全文获取类型
收费全文 | 508篇 |
免费 | 12篇 |
国内免费 | 5篇 |
专业分类
化学 | 334篇 |
晶体学 | 2篇 |
力学 | 15篇 |
数学 | 61篇 |
物理学 | 113篇 |
出版年
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 14篇 |
2013年 | 16篇 |
2012年 | 27篇 |
2011年 | 26篇 |
2010年 | 11篇 |
2009年 | 11篇 |
2008年 | 23篇 |
2007年 | 18篇 |
2006年 | 25篇 |
2005年 | 30篇 |
2004年 | 22篇 |
2003年 | 23篇 |
2002年 | 22篇 |
2001年 | 13篇 |
2000年 | 17篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 9篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1971年 | 4篇 |
1969年 | 2篇 |
1968年 | 3篇 |
排序方式: 共有525条查询结果,搜索用时 0 毫秒
81.
Christina Kjær Dr. Henriette Lissau Nina Katharina Gravesen Salinas Andreas Østergaard Madsen Dr. Mark H. Stockett Freja E. Storm Thomas Holm Hansen Prof. Jens Ulrik Andersen Prof. Bo W. Laursen Prof. Kurt V. Mikkelsen Prof. Mogens Brøndsted Nielsen Prof. Steen Brøndsted Nielsen 《Chemphyschem》2019,20(4):533-537
Being alone or together makes a difference for the photophysics of dyes but for ionic dyes it is difficult to quantify the interactions due to solvent screening and nearby counter ions. Gas-phase luminescence experiments are desirable and now possible based on recent developments in mass spectrometry. Here we present results on tailor-made rhodamine homodimers where two dye cations are separated by methylene linkers, (CH2)n. In solution the fluorescence is almost identical to that from the monomer whereas the emission from bare cation dimers redshifts with decreasing n. In the absence of screening, the electric field from the charge on one dye is strong enough to polarize the other dye, both in the ground state and in the excited state. An electrostatic model based on symmetric dye responses (equal induced-dipole moments in ground state) captures the underlying physics and demonstrates interaction even at large distances. Our results have possible implications for gas-phase Förster Resonance Energy Transfer. 相似文献
82.
Thin films of poly(methyl methacrylate) (PMMA) (25 nm) deposited on gold coated glass substrates have been locally modified by exposure to biased atomic force microscopy (AFM) tips. Constant exposure currents in the range of 0.5–0.65 nA leads to removal of PMMA both by direct ablation and enhanced solubility in a developer solution. Possible mechanisms causing such modifications have been discussed. Submicron Au structures were formed by combining AFM lithography, involving localized removal of PMMA, with sputter deposition of gold and a lift-off process. 相似文献
83.
In a sequence of papers, we will show that the existence of a (half) strongly-transitive automorphism group acting on a locally finite triangle building forces to be one of the examples arising from PSL3(K) for a locally finite local skewfield K. Furthermore, we introduce some Moufang-like conditions in affine buildings of rank 3, and characterize those examples arising from algebraic, classical or mixed type groups over a local field. In particular, we characterize the p-adic-like affine rank 3 buildings by a certain p-adic Moufang condition, and show that such a condition has zero probability to survive in hyperbolic rank 3 buildings. This shows that a construction of hyperbolic buildings as analogues of p-adic affine buildings is very unlikely to exist. 相似文献
84.
Abécassis B Testard F Arleth L Hansen S Grillo I Zemb T 《Langmuir : the ACS journal of surfaces and colloids》2007,23(20):9983-9989
By means of small-angle neutron scattering and conductivity measurements, we study the microstructure of octylammoniumoctanoate/octane/water catanionic reverse microemulsions with an excess of anionic or cationic surfactant. Increasing the surface charge makes the microemulsion able to incorporate much more water than in the neutral case, up to 10 water molecules per surfactant. Even with charges in the surfactant film, wormlike micelles are present in the microemulsion domain. Along water dilution lines, the classical rod-to-sphere transition due to the minimization of the curvature energy of the rigid surfactant film is observed. When temperature is decreased, a re-entrant phase transition associated with the liquid-gas equilibrium of attractive cylinders is observed. Using the framework of the Tlusty-Safran theory, attraction could originate from junctions between wormlike reverse micelles. In any case, the spontaneous curvature of the catanionic surfactant film depends on both the temperature and the net charge, whatever the sign of the latter. 相似文献
85.
Malene Steen Nielsen Flagga 《International Journal of Theoretical Physics》1999,38(8):2121-2161
Is time travel possible? While this paper doesnot answer the question, it does put forward a modelthat may one day answer it. The decoherent-historiesapproach to quantum mechanics is used in a nontrivial background provided by a wormhole whose mouthsreside in the same universe, but have a time differencebetween them. A charged scalar particle approaches thewormhole mouth in the present and is decohered spatially through the interaction with theCoulomb field of the wormhole mouth. 相似文献
86.
J.M. Lee K.G. Watkins W.M. Steen 《Applied Physics A: Materials Science & Processing》2000,71(6):671-674
Laser removal of small particles from a metal surface is carried out by changing the incident angle of the laser beam. It
has been found that a dramatic improvement of cleaning efficiency in terms of area and energy is observed when using the laser
at glancing angle of incidence as compared to perpendicular. Furthermore substrate damage is greatly reduced and probably
eliminated at glancing angles. The process mechanism is discussed by considering the adhesion and the laser-induced cleaning
forces for different incident angles. It is shown that there are different laser–matter interactions operating.
Received: 25 April 2000 / Accepted: 9 May 2000 / Published online: 5 October 2000 相似文献
87.
Bogdan Bogdanov Henri E. K. Matimba Steen Ingemann Nico M. M. Nibbering 《Journal of the American Society for Mass Spectrometry》1996,7(7):639-652
The mechanism of propene loss from protonated phenyl n-propyl ether and a series of mono-, di-, and trimethylphenyl n-propyl ethers has been examined by chemical ionization (CI) mass spectrometry in combination with tandem mass spectrometry experiments. The role of initial proton transfer to the oxygen atom and the aromatic ring, respectively, has been probed with the use of deuterated CI reagents, D2O, CD3OD, and CD3CN (given in order of increasing proton affinity), in combination with deuterium labeling of the β position of the n-propyl group or the phenyl ring. The metastable [M + D]+ ions of phenyl n-propyl ether—formed with D2O as the CI reagent—eliminate C3H5D and C3H6 in a ratio of 10:90, which indicates that the added deuteron is incorporated to a minor extent in the expelled neutral species. In the experiments with CD3OD as the CI reagent, the ratio between the losses of C3H5D and C3H6 from the metastable [M + D]+ ions of phenyl n-propyl ether is 18:82, whereas the ratio becomes 27:73 with CD3CN as the reagent. A similar trend in the tendency to expel a propene molecule that contains the added deuteron is observed for the metastable [M + D]+ ions of phenyl n-propyl ether labeled at the β position of the alkyl group. Incorporation of a hydrogen atom that originates from the aromatic ring in the expelled propene molecule is of negligible importance as revealed by the minor loss of C3H5D from the metastable [M + H]+ ions of C6D5OCH2CH2CH3 irrespective of whether H2O, CH3OH, or CH3CN is the CI reagent. The combined results for the [M + D]+ ions of phenyl n-propyl ether and deuterium-labeled analogs are suggested to be in line with a model that assumes that propene loss occurs not only from species formed by deuteron transfer to the oxygen atom, but also from ions generated by deuteron transfer to the ring. This is substantiated by the results for the methyl-substituted ethers, which reveal that the position as well as the number of methyl groups bonded to the ring exert a marked effect on the relative importances of the losses of C3H5D and C3H6 from the metastable [M + D]+ ions of the unlabeled methyl-substituted species. 相似文献
88.
Henrik Jacobsen Kim Lefmann Erik Brok Cathrine Frandsen Steen Mørup 《Journal of magnetism and magnetic materials》2012
Numerous studies of the low-temperature saturation magnetization of ferrimagnetic nanoparticles and diamagnetically substituted ferrites have shown an anomalous temperature dependence. It has been suggested that this is related to freezing of canted magnetic structures. We present models for the temperature dependence of the magnetization of a simple canted spin structure in which relaxation can take place at finite temperatures between spin configurations with different canting angles. We show that the saturation magnetization may either decrease or increase with decreasing temperature, depending on the ratio of the exchange coupling constants. This is in agreement with experimental observations. 相似文献
89.
Børge Bak Niels A. Kristiansen Henrik Svanholt Arne Holm Steen Rosenkilde 《Chemical physics letters》1981,78(2):301-303
Microwave Spectra of 13CH212C80,78Se and 12CH213C80,78Se (selenoketene) are recorded. B 5-13C-1,2,3-selenadiazole all four species are formed. The 13C scrambling may take place via a three-membered ring, selenirene, but as expected its microwave spectrum was not observed. 相似文献
90.
Maj‐Britt Suhr Kirketerp Michael Åxman Petersen Dr. Marius Wanko Dr. Leonardo Andres Espinosa Leal Henning Zettergren Dr. Françisco M. Raymo Prof. Angel Rubio Prof. Mogens Brøndsted Nielsen Prof. Steen Brøndsted Nielsen Prof. 《Chemphyschem》2009,10(8):1207-1209
From blue to red: While four π‐conjugated nitrophenolates absorb within a relatively narrow region in solution, they cover the entire visible spectrum when isolated in vacuo (see picture). The work combines gas‐ and solution‐phase spectroscopy and provides the first benchmark of theoretical excitation energies for nitrophenolates.