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921.
Anhydrous copper(II) furoate and copper(II) thiophene-2-carboxylate have been Synthesized. They are formulated as dimeric species with four carboxylate bridges. The thiophene and furan moieties give rise to polymeric structures. Electron spin resonance spectra and magnetic susceptibility measurements show that the dimers have a singlet ground state and a thermally populated triplet state. The exchange coupling constants, 2J, are ?322 and ?312 cm?1 for the furoate and thiophene-2-carboxylate complexes, respectively. The electronic and infrared spectra are also discussed. 相似文献
922.
The incorporation of three-fold symmetric organic host molecules into coordination polymers should allow for the construction of new and interesting network structures, capable of multiple inclusion behaviour. A range of new multi-dentate bridging ligands/molecular hosts have been prepared by appending nitrogen-containing heterocycles to either cyclotricatechylene, or cyclotriguaiacylene cores. These compounds were obtained in a single-step reaction from readily available precursors, with moderate to good yields, and characterised by a combination of NMR spectroscopy, mass spectrometry and elemental analysis. Two of the new compounds were characterised by X-ray crystallography, revealing different modes of self inclusion behaviour, which indicate the potential importance of [small pi]-donor stabilisation by CTV derivatives in host-guest chemistry. 相似文献
923.
P. J. Richardson J. H. D. Eland P. Lablanquie 《Journal of mass spectrometry : JMS》1986,21(5):289-294
Photoion-photoion coincidence spectra of benzene and benzene-d6 photoionized by He(II) light and synchrotron radiation show the existence of six major and eight minor charge-separation reactions of the [C6H6]2+ ion. Three main groups of ion pairs are related to [C3H3]+ + [C3H3]+, [C2H3]+ + [C4H3]+ and [CH3]+ + [C5H3]+, with appearance energies of 32.2 ± 0.5 eV, 31.3 ± 0.5 eV and 28.4 ± 0.3 eV. The kinetic energy release is the same for all pairs within a group, irrespective of hydrogen number, but differs from group to group. Results are interpreted in terms of fast, direct charge separation of [C6H6]2+, and subsequent hydrogen loss by the singly charged fragments. 相似文献
924.
925.
926.
Rachael Padman Glenn J. White Robert Barker Dennis Bly Nick Johnson Hugh Gibson Matt Griffin J. Anthony Murphy Richard Prestage John Rogers et al. 《International Journal of Infrared and Millimeter Waves》1992,13(10):1487-1513
A dual-polarization InSb hot-electron bolometer-mixer receiver has been built for the James Clerk Maxwell Telescope, for operation at 461 and 492 GHz (the frequencies of theJ=43 rotational transition of CO and of the3
P
13
P
0 transition of neutral carbon). Receiver noise temperatures of 500K have been obtained at 461 GHz, in observing bandwidths of 3 MHz. The receiver was designed as a common-user or facility instrument. Here we describe those aspects of the design and construction which enabled this goal to be realized. 相似文献
927.
928.
Richardson NA Gu J Wang S Xie Y Schaefer III HF 《Journal of the American Chemical Society》2004,126(13):4404-4411
The deoxyribonucleosides have been studied to determine the properties of combinations of 2-deoxyribose with each of the isolated DNA bases for both neutral and anionic species. We have used a carefully calibrated theoretical method [Chem. Rev. 2002, 102, 231], employing the B3LYP hybrid Hartree-Fock/DFT functional with the DZP++ basis set. Predictions are made of the geometric parameters, adiabatic electron affinities, charge distributions based on natural population analysis, and decomposition enthalpy for the neutral and anionic forms of the four 2'-deoxyribonucleosides in DNA: 2'-deoxyriboadenosine (dA), 2'-deoxyribocytidine (dC), 2'-deoxyriboguanosine (dG), and 2'-deoxyribothymidine (dT). Geometric changes in the anions show that the glycosidic bond exhibits little change with excess charge for the guanosine but significant shortening for the adenosine and for the pyrimidines. The zero-point corrected adiabatic electron affinities in eV for each of the 2'-deoxyribonucleosides are as follows: 0.06, dA; 0.09, dG; 0.33, dC; and 0.44, dT. These values are uniformly greater than those of the corresponding isolated bases (-0.28, A; -0.07, G; 0.03, C; 0.20, T) and the isolated 2-deoxyribose (-0.38) at the same level of theory. The vertical detachment energies of dT and dC are substantial, 0.72 and 0.94 eV, and these anions should be observable. A high VDE, 0.91 eV, is also found for dA but its anion is unlikely to be stable due to the small AEA of 0.06 eV. The high VDE reflects the fact that the molecular structures of the anions and the corresponding neutral species are quite different. Valence character is displayed for the SOMOs of dA, dC, and dT, while some component of diffuse character is visible in the SOMO of dG. Further analysis of electronic changes upon electron attachment include an examination of the NPA charges, which show that in the neutral 2'-deoxyribonucleosides the sum of NPA charges for every base is the same, -0.28 with the sum of 2-deoxyribose charges being positive, +0.28. In the anions, the trend in charge division varies based on the nature of the excess electron in the anions. Thermodynamically, the overall enthalpy change for the reaction of water with the neutral nucleosides to give bases and ribose is approximately zero. The analogous decomposition is exothermic by 8 to 11 kcal mol-1 for the anions, indicating possible challenges for anionic gas-phase nucleoside exploration in the presence of water. 相似文献
929.
Kaufman Eric N. Cooper Stanley P. Budner Maria K. Richardson Gerald R. 《Applied biochemistry and biotechnology》1996,57(1):503-515
Applied Biochemistry and Biotechnology - A continuous biparticle fluidized-bed reactor (BFBR) is developed for the simultaneous fermentation and recovery of lactic acid. In this processing scheme,... 相似文献
930.
Nghiem Nhuan P. Davison Brian H. Suttle Bruce E. Richardson Gerald R. 《Applied biochemistry and biotechnology》1997,(1):565-576
The effect of an external supply of carbon dioxide and pH on the production of succinic acid byAnaerobiospirillum succiniciproducens was studied. In a rich medium containing yeast extract and peptone, when the external carbon dioxide supply was provided
by a 1.5M Na2CO3 solution that also was used to maintain the pH at 6.0, no additional carbon dioxide supply was needed. In fact, sparging
CO2 gas into the fermenter at 0.025 L/L-min or higher rates resulted in significant decreases in both production rate and yield
of succinate. Under the same conditions, the production of the main by-product acetate was not affected by sparging CO2 gas into the fermenter. The optimum pH (pH 6.0) for the production of succinic acid was found to be in agreement with results
previously reported in the literature. Succinic acid production also was studied in an industrial-type inexpensive medium
in which light steep water was the only source of organic nutrients. At pH 6.0 and with a CO2 gas sparge rate of 0.08 L/L-min, succinate concentration reached a maximum of 32 g/L in 27 h with a yield of 0.99 g succinate/g
glucose consumed. 相似文献