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31.
32.
We present a convenient method for accounting for the anisotropy of partially filled d shells that are incorporated in effective core potentials by including the leading anisotropy term of the d-type electron density, which is the quadrupole moment, as an electrostatic potential energy operator in the model Hamiltonian. We present sample calculations on the cobalt hydride and dicobalt systems. We find the quadrupole anisotropy to have a very large effect in the distance regime of CoH. In the dicobalt system, which has a relatively long internuclear distance, the quadrupole anisotropy shifts the equilibrium bond length by nearly 0.02 bohr. 相似文献
33.
W A Erdman N A Breslau J C Weinreb P Weatherall H Setiawan R Harrell W Snyder 《Magnetic resonance imaging》1989,7(2):187-194
Thirty-two (32) patients with primary hyperparathyroidism (17 with prior localization surgery, 15 without) were studied by a combination of computed tomography (CT), ultrasound (US), nuclear medicine (NM), and magnetic resonance imaging (MRI) for parathyroid adenoma localization. The sensitivity and true-positive ratio of each imaging technique and various combinations of techniques were evaluated. Of the 28 proven parathyroid adenomas (27 by surgery, 1 by digital subtraction angiography), 24 were imaged by two techniques, 19 by three techniques, and 10 by all four imaging techniques. The sensitivities were NM (65%), CT (76%), US (77%), and MRI (81%). The differences between true-positive ratios of 82%, 64%, 71%, and 77%, respectively, were not statistically significant. If multiple techniques were considered as a single test (i.e., a positive localization requires two or more tests to be positive at the same location), then sensitivity for a two-study combination was 79% and true-positive ratio 86%. Three techniques showed a sensitivity of 63% and a true-positive ratio of 92%, four modalities 40% and 100%, respectively. There was no significant difference in the various combinations of techniques employed (e.g., CT and US, US and MR, NM and MR, etc.). Thus, there appears to be an advantage in performing multiple techniques (regardless of which combination is selected) until two tests are positive at the same location. 相似文献
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35.
Siwy Z Heins E Harrell CC Kohli P Martin CR 《Journal of the American Chemical Society》2004,126(35):10850-10851
Ion channels are protein pores that span cell membranes and open and close in response to stimuli like changes in the transmembrane potential, binding of a ligand, or mechanical stress. When open, ions pass through the pore, and hence across the cell membrane, and when closed, ion-transport is precluded. Hence, these channels are nanodevices that have a current-rectification function. There is intense research effort aimed at understanding the molecular-level mechanism for this function. One approach for elucidating the mechanism is to construct a simple abiotic system that mimics this function and to use the mechanistic details of this mimic as a guide to understand the more complex biological channel. We describe here such an abiotic mimic: a synthetic membrane that contains a single conical gold nanotube. The advantage of this mimic is that the surface charge and chemistry of the nanotube wall can be varied, at will, by judicious choice of electrolyte or by thiol chemisorption. This has allowed us to make conical Au nanotubes that rectify the ion current and, just as importantly, to definitively elucidate the mechanism of this function. 相似文献
36.
J. R. Harrell J. B. Lutz J. L. Kelly 《Journal of Radioanalytical and Nuclear Chemistry》1988,127(1):13-20
The partition coefficient of hypoiodous acid at 20 °C has been determined to be 930. This determination is based on measured values of the instantaneous iodine partition coefficient /IPC/ vs. time after the introduction of molecular iodine into an air-water system at pH=9. 相似文献
37.
Our previous work with PVC plastisols showed that pseudo-plastic behavior under increasing frequency of dynamic measurement was a result of the development of an immobilized layer. Subsequently, the dynamic viscosity and the storage modulus of the mobile phase were evaluated. The samples consisted of fine and coarse particles, of which the fine/coarse ratio was varied. The present work relates the storage modulus at different frequencies to the fine/coarse ratio through a model network consisting of particle-particle contacts. The contacts are of three kinds, fine-fine (f-f), fine-coarse (f-c), and coarse-coarse (c-c). The average number of contact points per particle has been evaluated for the above kinds of contacts at different frequencies. Also, a number of particles participating in the network have been evaluated as a relative measure. At lower frequency relatively larger numbers of f-f contact points exist per particle but fewer numbers of particles participate in the network. Therefore, the network is rather loose. The f-c contact shows a similar trend but fewer contact points per particle at all frequency levels. The c-c contact is limited to a pair formation, i.e., only 0.5 contact point per particle on average. However, c-c contact contributes significantly to the magnitude of the modulus, because of the size of the particle. At the higher frequency there are fewer f-f contacts, but a larger number of particles are participating in the network. The trend with the f-c contact is very similar. The c-c contact increases significantly at the higher frequencies. 相似文献
38.
Kang S Miao GX Shi S Jia Z Nikles DE Harrell JW 《Journal of the American Chemical Society》2006,128(4):1042-1043
Self-assembled FePt/MnO nanoparticles with different morphology and size were synthesized with a polyol process. With the MnO coating, FePt nanoparticles exhibit a high blocking temperature and magnetic moment. The low-temperature hysteresis loop of FePt nanoparticles can be shifted through the AFM pinning of the MnO shell. The aggregation of FePt nanoparticles during the L10 phase transformation can be significantly decreased by coating with the MnO shell. 相似文献
39.
40.
A fluorescent probe based on silicon quantum dots (SiQDs) was developed for the selective and sensitive detection of oxytetracycline (OTC) via the inner filter effect (IFE). The water-soluble fluorescent SiQD was synthesized based on the reaction of 3-Aminopropyltriethoxysilane (APTES) and sodium citrate as precursors by the one-pot hydrothermal process. The strong fluorescence emission of quantum dots (QDs) was obtained at 440 nm when excited at 350 nm and OTC had a broad absorption band between 200 and 400 nm. The excitation spectrum of SiQDs was completely overlapped with the absorption spectrum of OTC. The light at an excitation wavelength of QDs absorbed by OTC caused a decrease in fluorescence intensity with an increase in the concentration of OTC. Under optimal conditions, the linear concentration range was 0.92–9.2 µg mL1 with a detection limit (LOD; S/N = 3) of 0.19 µg mL -1 . The proposed method was applied to the determination of OTC in milk samples and satisfactory recoveries (98.8–100.5%) with low RSD % values (0.93–2.31%) were achieved. This simple, selective, sensitive, rapid, and cheap method can be used as a promising tool for OTC analysis in food safety. 相似文献