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81.
Horst-Henning Grotheer Johann Wolfgang Hammer Klaus-Werner Hoffmann 《Zeitschrift für Physik A Hadrons and Nuclei》1969,225(4):293-302
The electron capture decay of85Sr and55Y has been investigated using NaI(Tl)-detectors. Spectroscopic-coincidence techniques have been employed to examine theK-electron capture rates. The experimental results areP K ω K (Sr)=.5959 ± 0.0035 andP K ω K (Y)=0.6340± 0.0032. Using theK-capture probabilities, derived from the capture ratios ofBrysk andRose with the exchange correction ofBahcall:P K (Sr)=0.880± 0.008 andP K (Y)=0.883 ± 0.008, one can derive from these results the fluorescence yieldsω K (Rb)=0.677± 0.009 andω K (Sr)=0.712± 0.010. Functions ofω K (Z) were fitted to recent experimental data and tabulated forZ=5–90. In addition to these results the half life of the 514 keV state of85Rb and the branching ratios and the positron rate of the88Y-decay have been measured with the same techniques. The data obtained partly disagree from measurements of other authors. 相似文献
82.
Hammer NI Early KT Sill K Odoi MY Emrick T Barnes MD 《The journal of physical chemistry. B》2006,110(29):14167-14171
Size-correlated single-molecule fluorescence measurements on CdSe quantum dots functionalized with oligo(phenylene vinylene) (OPV) ligands exhibit modified fluorescence intermittency (blinking) statistics that are highly sensitive to the degree of ligand coverage on the quantum dot surface. As evidenced by a distinct surface height signature, fully covered CdSe-OPV nanostructures (approximately 25 ligands) show complete suppression of blinking in the solid state on an integration time scale of 1 s. Some access to dark states is observed on finer time scales (100 ms) with average persistence times significantly shorter than those from ZnS-capped CdSe quantum dots. This effect is interpreted as resulting from charge transport from photoexcited OPV into vacant trap sites on the quantum dot surface. These results suggest exciting new applications of composite quantum dot/organic systems in optoelectronic systems. 相似文献
83.
The adhesion properties and catalytic activity of rutile TiO(2)(110)-supported Au(7) nanoclusters in different oxidation states are investigated by means of density functional theory. The calculations cover both surface science conditions of reduced TiO(2) and real catalyst conditions of oxidized (alkaline) TiO(2) supports. Large adhesion energies of Au(7) are found only when modeling real catalysts where the cluster becomes cationic with Au(+) ions in Au-O or Au-OH bonds. The full catalytic cycle for oxidation of CO by O(2) over Au(7) on alkaline TiO(2)(110) is calculated and found to involve only small activation barriers. In the presence of the CO reductant, the Au(+) sites are capable of cycling between bonding of atomic and molecular oxygen. We confirm our findings by comparison of calculated and experimental infrared stretch frequency data for adsorbed CO. 相似文献
84.
Mark Lenkewitz Evgeny Epelbaum H. -W. Hammer Ulf-G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2013,49(2):1-11
We calculate the electromagnetic neutral pion production off tri-nucleon bound states (3H, 3He) at threshold in chiral nuclear effective field theory to fourth order in the standard heavy baryon counting. We show that the fourth-order two-nucleon corrections to the S-wave multipoles at threshold are very small. This implies that a precise measurement of the S-wave cross section for neutral pion production off 3He allows for a stringent test of the chiral perturbation theory prediction for the S-wave electric multipole $E_{0+}^{\pi^0 n}$ . 相似文献
85.
86.
In this paper we present a super-resolved Raman spectroscopy configuration where, due to the proposed resolution improvement, more chemical species can be simultaneously detected. The idea includes usage of the basic property of Raman in which shifting the excitation wavelength will shift the absolute wavelength of the Raman spectral lines. Thus, encoding the spectra prior to analysis by the spectrometer allows obtaining spectral super-resolved sensing via time multiplexing super-resolution concepts applied over the spectral domain. 相似文献
87.
Synthesis of phthalocyanines with asymmetrical substitution on the periphery is often difficult due the problems in purification of the phthalocyanine mixtures obtained. Using a poly(ethylene glycol) (PEG)-based support with a Wang-type linker, we have developed the synthesis of monohydroxylated, oligoethylene glycol substituted phthalocyanines utilizing an amidine-base-promoted phthalonitrile tetramerization reaction. The use of a hydrophilic support allows symmetrical phthalocyanine product formed in solution to be readily and completely removed by washing while leaving the "AB3" product on the support. Acid cleavage with 10% trifluoroacetic acid provides the pure unsymmetrically substituted Pc. This method was applied to several metallo Pcs. Additionally, methods to avoid premature reactions on-resin that give A2B2 products are provided. 相似文献
88.
Chathuranga S. L. Rathnamalala Selena Hernandez Dr. Melissa Y. Lucero Chelsea B. Swartchick Dr. Abdul Kalam Shaik Prof. Dr. Nathan I. Hammer Amanda K. East Prof. Dr. Steven R. Gwaltney Prof. Dr. Jefferson Chan Prof. Dr. Colleen N. Scott 《Angewandte Chemie (International ed. in English)》2023,62(13):e202214855
Shortwave infrared (SWIR) dyes are characterized by their ability to absorb light from 900 to 1400 nm, which is ideal for deep tissue imaging owing to minimized light scattering and interference from endogenous pigments. An approach to access such molecules is to tune the photophysical properties of known near-infrared dyes. Herein, we report the development of a series of easily accessible (three steps) SWIR xanthene dyes based on a dibenzazepine donor conjugated to thiophene ( SCR-1 ), thienothiophene ( SCR-2 ), or bithiophene ( SCR-3 ). We leverage the fact that SCR-1 undergoes a bathochromic shift when aggregated for in vivo studies by developing a ratiometric nanoparticle for NO ( rNP-NO ), which we employed to successfully visualize pathological levels of nitric oxide in a drug-induced liver injury model via deep tissue SWIR photoacoustic (PA) imaging. Our work demonstrates how easily this dye series can be utilized as a component in nanosensor designs for imaging studies. 相似文献
89.
Competition between Hydrophilic and Argyrophilic Interactions in Surface Enhanced Raman Spectroscopy 下载免费PDF全文
John T. Kelly Annie K. McClellan Lynn V. Joe Ashley M. Wright Lawson T. Lloyd Prof. Gregory S. Tschumper Prof. Nathan I. Hammer 《Chemphyschem》2016,17(18):2782-2786
The competition for binding and charge‐transfer (CT) from the nitrogen containing heterocycle pyrimidine to either silver or to water in surface enhanced Raman spectroscopy (SERS) is discussed. The correlation between the shifting observed for vibrational normal modes and CT is analyzed both experimentally using Raman spectroscopy and theoretically using electronic structure theory. Discrete features in the Raman spectrum correspond to the binding of either water or silver to each of pyrimidine's nitrogen atoms with comparable frequency shifts. Natural bond orbital (NBO) calculations in each chemical environment reveal that the magnitude of charge transfer from pyrimidine to adjacent silver atoms is only about twice that for water alone. These results suggest that the choice of solvent plays a role in determining the vibrational frequencies of nitrogen containing molecules in SERS experiments. 相似文献
90.