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101.
T. M. Healy A. A. Fontaine J. T. Ellis S. P. Walton A. P. Yoganathan 《Experiments in fluids》1998,25(5-6):512-518
In this work, a flow visualization experiment was performed to elucidate features of the retrograde hinge flow through a
5 : 1 scaled model of the Medtronic Parallel bileaflet heart valve. It was hypothesized that this model would provide detailed
flow information facilitating identification of flow structures associated with thrombus formation in this valve. The experimental
protocol was designed to ensure fluid dynamic similarity between the model and prototype heart valves. Flow was visualized
using dye injection. The detailed flow structures observed showed the hinge’s inflow channel was the most suspect region for
thrombus formation. Here a complex helical structure was observed.
Received: 27 October 1997/Accepted: 1 May 1998 相似文献
102.
In a fundamental paper on the algebraic theory of graph colouring Tutte [2] proves that the only tangential 1-block over GF(2) is the geometry corresponding to the polygon matroid of the graph K3. For a good discussion of the problem and a direct proof of Tutte's theorem see Aigner [1, p. 373].
The purpose of this note is to prove the following result. 相似文献
103.
104.
Rhenium 4f, chlorine 2p and oxygen 1s binding energies have been recorded for a series of coordination complexes of rhenium(V) and rhenium(VII) containing rhenium-oxygen bonds. Related studies on the rhenium(III) acetates Re2(OAc)4X2(X = Cl, Br) and on several adducts of the rhenium chlorides (Re 4f and Cl 2p binding energies only) are also reported. Chemical shift data are related where possible to the molecular structures of the complexes. Correlations between rhenium 4f binding energies and oxidation state are of diagnostic value only in distinguishing the high oxidation state species (rhenium(V) and (VII)). Differences in rhenium 4f and oxygen 1s binding energies [δ(O1s, Re 4f)] may be useful in probing the nature of the rhenium-oxygen bonds. 相似文献
105.
106.
For the first time, an anisotropic graphite furnace heated by capacitive discharge was used for laser-excited atomic fluorescence spectrometry. A detection limit of 5 fg for thallium was obtained with a laser repetition rate of 500 Hz and a peak integration time of 80 ms. The use of a capacitive discharge furnace allows for a shorter integration time, which in turn should allow for integration of less background noise, and improved detection limits. Theoretically, the magnitude of the shot noise should be proportional to the square root of the integration time, and inversely proportional to the square root of the laser repetition rate. Experimental data illustrated the effect of laser repetition rate, but were inconclusive with respect to integration time. The linear dynamic range of the calibration curve was six orders of magnitude, which was comparable to that normally obtained for laser-excited atomic fluorescence in modern commercial graphite furnaces. Thallium was accurately determined in NIST biological samples at levels one to two orders of magnitude below the detection limit of electrothermal atomic absorption spectrometry, with an analytical precision between 8 and 20%. The interference effects of calcium, sodium chloride, and potassium chloride on the thallium signal were investigated and shown to be similar to both laser-excited atomic fluorescence in a conventional furnace and capacitive discharge furnace atomic absorption results reported in the literature. 相似文献
107.
Electrochemical methods can be applied in a number of ways as detection systems for competitive immunoassays, especially through the use of redox-labelled antigens. To overcome the problem of detection of such conjugates at low concentration, a system is described in which a poly(vinylferrocene)-modified glassy carbon electrode is used to accumulate charge from solution glucose/glucose oxidase via the intermediacy of a redox-labelled antigen, cycled repeatedly between the enzyme and the electrode. The charge accumulated by the electrode is measured electrochemically by returning the electrode to its original potential and integrating the resulting current-time transient. The charge is proportional to the concentration of redox-labelled antigen in solution and to the charge-accumulation time. In this way 1,1'-dimethylferrocene-ethan-1-ol-2-amine was reproducibly detected to 0.9 nM, with a 10 min incubation period. The 8-ferrocenyl conjugate of theophylline was characterised as a model system for possible application in a higher sensitivity electrochemical immunoassay. 相似文献
108.
We show that the evolution equations for a perfect fluid coupled to general relativity in a general lapse and shift, are Hamiltonian relative to a certain Poisson structure. For the fluid variables, a Lie-Poisson structure associated to the dual of a semi-direct product Lie algebra is used, while the bracket for the gravitational variables has the usual canonical symplectic structure. The evolution is governed by a Hamiltonian which is equivalent to that obtained from a canonical analysis. The relationship of our Hamiltonian structure with other approaches in the literature, such as Clebsch potentials, Lagrangian to Eulerian transformations, and its use in clarifying linearization stability, are discussed.Research supported in part by NSF grant MCS 81-08814(A02)Research supported in part by NSF grant MCS 81-07086 相似文献
109.
The effect of seasonal temperature change on the release of methylated arsenic from macroalgae, phytoplankton and sediment porewaters has been investigated by a series of controlled laboratory experiments. The appearance of dissolved arsenic species in the overlying waters was monitored using a coupled hydride generation/GC AA analytical technique. The liberation of dissolved arsenic species by the macroalgae Ascophyllum nodosum was examined under estuarine conditions at 5 °C and 15 °C. At the lower temperature the release rates were 0.2 μg kg?1 h?1 (wet weight of material) for monomethylarsenic (MMA) and 0.5 μg kg?1 h?1 for dimethylarsenic (DMA), whereas at 15 °C the rates were 0.4 μg kg?1 h?1 and 3.2 μg kg?1h?1, respectively. Incubation experiments were also carried out at 15 °C using the diatom Skeletonema costatum. During the log growth phase, when chlorophyll a concentrations were in the range 1-5 μg dm?3, the rate of appearance of DMA in the water was ~3 ng dm?3 h?1. Sediment samples from the freshwater and seawater end-members of the Tamar Estuary, UK, were incubated under natural conditions at 5 °C and 15 °C. The freshwater sediments released DMA in preference to MMA; the concentrations of both species increased exponentially and reached a steady state in the overlying water after 250 h. Considerably more DMA was produced at 15 °C than at 5 °C, whilst the amount of MMA produced appeared to be insensitive to the temperature increase. In contrast, the seawater sediments always produced more MMA than DMA and the increase in temperature had little effect on the production of either MMA or DMA. The results of the laboratory experiments were compared with field observations in temperate estuaries, including the Tamar Estuary. The implications of changes of water temperature on the fate of arsenic in estuaries is discussed and modifications to the estuarine arsenic cycle are proposed. 相似文献
110.
Tetramethyllead (TML) has been produced from inorganic lead salts using biologically active sediments and waters from the Tamar Estuary, S. W. England. The TML production was a two-stage process involving an initial lag phase of about 100 hours followed by the exponential appearance of TML, which amounted to about 0.03% of total added lead. The methylation process is discussed in the context of lead transport in estuaries. 相似文献