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排序方式: 共有520条查询结果,搜索用时 15 毫秒
31.
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Schumm BA Koetke DS Adolphsen CE Alexander JP Averill D Barish BC Barklow T Barnett BA Blockus D Boyarski A Brabson B Breakstone A Bulos F Burchat PR Burke DL Cence RJ Chapman J Chmeissani M Cords D Coupal DP Dauncey P DeStaebler HC Dorfan JM Drell PS Drewer DC Durrett D Elia R Feldman GJ Field RC Ford WT Fordham C Frey R Fujino D Gan KK Gero E Gidal G Glanzman T Goldhaber G Gomez Cadenas JJ Gratta G Hanson G Harr R Harral B Harris FA Hayes K Hearty C Heusch CA Hildreth MD Himel T Hinshaw DA 《Physical review D: Particles and fields》1992,46(1):453-456
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Wilson MH Ledwaba LP Field JS McMillin DR 《Dalton transactions (Cambridge, England : 2003)》2005,(16):2754-2759
As part of an effort to develop new lumaphors involving late transition metal ions, this report describes the synthesis and characterization of the first platinum(II) derivatives containing 2,2':6',2'-terpyridine (trpy) and cyanide as co-ligands. According to existing models, including cyanide in the coordination sphere should raise the energies and minimize the influence of short-lived d-d excited states that otherwise compromise the excited-state lifetime. Both [Pt(trpy)(CN)]+ and the 4'-cyano-2,2':6',2'-terpyridine analogue [Pt(CN-T)(CN)]+ are emissive in dichloromethane solution, but the signals are weak. Part of the problem is that the d-pi* charge-transfer excited states also rise in energy, so that the emission actually originates from a (3)pi-pi* state with a relatively low radiative rate constant. However, another member of the series, the 4'-dimethylamino-2,2':6',2'-terpyridine (dma-T) derivative [Pt(dma-T)(CN)]+, proves to be a very promising platform with an emission quantum yield of phi= 0.26 and an excited-state lifetime of tau = 22 micros in room-temperature, deoxygenated dichloromethane solution. In the dma-T complex the electron-rich dimethylamino substituent provides the basis for an emissive, but largely ligand-based, charge-transfer excited state. The orbital parentage is such that the photoluminescence persists in donating solvents like dimethylformamide, which ordinarily quenches d-pi* excited states in complexes of this type. 相似文献
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Siegfried E. Drewes Owen L. Njamela Neville D. Emslie Niyum Ramesar John S. Field 《合成通讯》2013,43(20):2807-2815
The acrylate ester of salicylaldehyde, in the presence of DABCO, affords a crystalline coumarin salt. Formation of this derivative confirms a vital intermediate in the mechanism of the reaction. Salicylaldehyde, suitably protected, reacts with methyl acrylate to afford a novel coumarin not unlike the vasodilator chromonar. 相似文献
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Thomas H. Walter Bonnie A. Alden Kenneth Berthelette Jessica A. Field Nicole L. Lawrence Justin McLaughlin Amit V. Patel 《Journal of separation science》2022,45(8):1389-1399
We have characterized a sulfobetaine stationary phase based on 1.7 μm ethylene-bridged hybrid organic–inorganic particles, which is intended for use in hydrophilic interaction chromatography. The efficiency of a column packed with this material was determined as a function of flow rate, demonstrating a minimum reduced plate height of 2.4. The batch-to-batch reproducibility was assessed using the separation of a mixture of acids, bases, and neutrals. We compared the retention and selectivity of the hybrid sulfobetaine stationary phase to that of several benchmark materials. The hybrid sulfobetaine material gave strong retention for polar neutrals and high selectivity for methyl groups, hydroxy groups, and configurational isomers. Large differences in cation and anion retention were observed among the columns. We characterized the acid and base stability of the hybrid sulfobetaine stationary phase, using accelerated tests at pH 1.3 and 11.0, both at 70°C. The results support a recommended pH range of 2–10. We also investigated the performance of columns packed with this material for metal-sensitive analytes, comparing conventional stainless steel column hardware to hardware that incorporates hybrid surface technology to mitigate interactions with metal surfaces. Compared to the conventional columns, the hybrid surface technology columns showed a greatly improved peak shape. 相似文献
40.
M. A. Śmiałek N. C. Jones R. Balog N. J. Mason D. Field 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,62(2):197-203
Experiments were carried out to determine the dependence of the physical form of supercoiled DNA films on the initial temperature
of the substrate. Such films are often used in irradiation experiments involving low energy particles, like electrons or photons.
In order to obtain absolute values for cross sections for such experiments, the spatial distribution of the sample in the
film has to be well estimated. These investigations aim to correlate the size and form of a DNA film with the initial temperature
of the substrate, on which the liquid sample is deposited prior to evacuation. From our previous studies we concluded that
the presence of agents preventing DNA structural water evaporation is required in order to preserve the supercoiled plasmid
DNA form under vacuum conditions. Therefore, we examined the temperature dependence on films prepared from plasmid suspended
in solutions containing magnesium hydroxide, Tris-Cl buffer and various concentrations of sodium hydroxide.
To visualise the films we used a conventional light microscope with a CCD camera and a scanning electron microscope. The results
revealed a significant influence of the temperature of the substrate on both the area of the substrate covered by the film
as well as on the spatial distribution of DNA molecules. An increase in the amount of sodium hydroxide that stabilises supercoiled
DNA under vacuum increases DNA aggregation. After these investigations we conclude that the best temperature of the substrate
to produce uniform and thin films should be between –5 °C and -10 °C for substrates which are not atomically flat and above
0 °C for atomically flat substrates. 相似文献