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11.
Protein kinase C phosphorylates the neurone-specific protein B-50 at a single Ser41 residue, which is also the point for a major proteolytic cleavage in vitro, and probably in vivo, that produces a B-50 phosphorylation-inhibiting N-terminal fragment and a large C-terminal metabolite B-60 (B-50(41-226]. The intact purified protein will bind to calmodulin in the absence of calcium, but the interaction has an absolute requirement for dephospho-B-50. In an attempt to unify two aspects of B-50 biochemistry, we have examined the interaction of B-50 binding to calmodulin and B-50 proteolysis. HPLC- and affinity-purified B-50 bound to calmodulin, but purified B-60 did not. To ensure that this effect was not due to the phosphorylation state of pure, isolated B-60, the metabolite was generated in vitro using a Triton extract of synaptosomal plasma membranes, which contains the as yet uncharacterized B-50 protease. B-60 derived from dephospho-B-50 also failed to bind calmodulin. The results demonstrate a direct connection between B-50 binding to calmodulin and B-50 proteolysis. The position of the proposed calmodulin-binding domain within intact B-50 is discussed in light of the failure of calmodulin to bind B-60. 相似文献
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Abstract. Although there are many studies in searching for the most useful community diversity index, the importance of choosing an appropriate parameter has been neglected. Here, we examined dominance and diversity in early post-fire chaparral communities using different variables, i.e. plant density, cover and biomass. Significant different results were produced by applying different parameters and the difference may be caused by the inconsistency in density, cover, and biomass allocated in each life form. Among the three parameters, biomass was most successful in detecting differences among communities because the apportionment of biomass among species was more variable than that of density. Although the three species variables represent different aspects of community properties and their relative performance may vary among communities, we recommend the use of biomass or productivity data as the most appropriate variable because it can best represent per capita resource use and resource partitioning among organisms in competitive situations. 相似文献
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Rat livers were fractionated to obtain intracellular membrane preparations and a highly purified preparation of bile canaliculi. The fraction containing bile canaliculi was homogenized and subfractionated to give fractions representing fragments of contiguous membrane and of canalicular microvilli. The relative purity and extent of contamination of each preparation was determined. When the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene was incorporated into aliquots of each fraction at the same probe: lipid ratio and the steady-state anisotropy of its fluorescence measured, it was found that the plasma membrane preparations were much more ordered than the intracellular membrane preparations. Of the plasma membrane preparations, that containing the canalicular microvilli was the most ordered, even allowing for any contribution of contaminants. Thus the microvillus membrane of the bile canaliculus appears to be the most ordered domain of the plasma membrane of the hepatocyte. The high order in this domain may be a factor in reducing the susceptibility to bile salt damage during bile secretion, since it is this region which is exposed to high concentrations of bile salts in vivo. 相似文献
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Samples of great knots (Calidris tenuirostris) were collected in an earlier project, before and after a 5420‐km migration stage from Australia to China (believed to be flown non‐stop) to determine the mass of fat consumed, and also the mass of protein withdrawn from the flight muscles and other organs. The flight was simulated by a “time‐marching” computation, which calculated the fuel energy required, and allowed different hypotheses to be tried for the consumption of protein. The simulation predicted that the great knots would take about 4 days to cover the distance, in agreement with field estimates. Realistic predictions of the consumption of fat and protein were obtained by setting the conversion efficiency to 0.23 and the body drag coefficient to 0.10, withdrawing sufficient protein from the flight muscles to keep the specific work in the myofibrils constant throughout the flight, and taking enough additional protein from other tissues to bring the energy derived from oxidising protein to 5% of the total energy consumed. The same computation was applied to published data on the pre‐migration body composition of bar‐tailed godwits (Limosa lapponica), which are said to migrate over 10 000 km from Alaska to New Zealand. The computed range for a sample killed by collision with an obstruction, while actually departing from Alaska, was sufficient to reach the South Pole. A second sample, shot before departure from New Zealand, would have run out of fat before reaching Alaska, but could easily have reached northern Australia, where these godwits stage on their northbound migration. The higher range estimate for the Alaskan birds was not due to higher fat mass (only 5% difference) but to a higher fat fraction, which they had achieved by reducing the mass of other organs before departure. Some recent observations of high chemical power, observed in wind tunnel experiments, have been interpreted as being due to much lower conversion efficiency than the value of 0.23 assumed here, but this interpretation is flawed. Measurements of mechanical power from another wind tunnel project were also unexpectedly high, suggesting that unsteady flight by wind tunnel birds increases their power requirements, both mechanical and chemical, with no implications for efficiency. The calculated power is for “steady horizontal flight”, meaning that a valid test of predicted power requires birds to be trained to hold a constant position in the test section, while maintaining a steady wingbeat frequency and amplitude. This has not been achieved in recent experiments, and is hard to achieve when using physiological methods, because of the long periods of continuous flight needed. Measurements of mechanical rather than chemical power require shorter flight times, and offer better prospects for reliable power measurements. 相似文献
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Valic Zoran; Vidruk Edward H.; Ruble Stephen B.; Buckwalter John B.; Clifford Philip S. 《Journal of applied physiology》2001,90(1):23-28
To investigate whether efferent parasympathetic fibers to the trachealsmooth muscle course through the pararecurrent nerve rather than therecurrent or the superior laryngeal nerve, we stimulated all threenerves in anesthetized dogs. We also recorded the pararecurrentnerve activity response to bronchoconstrictor stimuli and compared itwith pressure changes inside a saline-filled cuff of an endotrachealtube. Electrical stimulation (30 s, 100 Hz, 0.1 ms, 10 mA) increasedtracheal cuff pressure by 21.0 ± 3.2 and 1.3 ± 0.7 cmH2O for the pararecurrent and the recurrent laryngealnerve, respectively. Stimulation of the superior laryngeal nerveincreased tracheal cuff pressure before, but not after, sectioning ofthe ramus anastomoticus, which connects it to the pararecurrent nerve.Intravenous administration of sodium cyanide increased pararecurrentnerve activity by 208 ± 51% and tracheal cuff pressure by14.4 ± 3.5 cmH2O. Elevation of end-tidalPCO2 to 50 Torr increased pararecurrent nerveactivity by 49 ± 19% and tracheal cuff pressure by 8.4 ± 3.6 cmH2O. Further elevation to 60 Torr increasedpararecurrent nerve activity by 101 ± 33% and tracheal cuffpressure by 11.3 ± 2.9 cmH2O. These results lead usto the conclusion that parasympathetic efferent fibers reach the smoothmuscle of the canine trachea via the pararecurrent nerve. 相似文献
20.
The fluorescence of the lipophilic prbe N-phenyl-1-naphthylamine (NPN) bound to intact cells of Escherichia coli is quenched by the addition of glucose, succinate,
-lactate, pyruvate, formate and glycerol. Partial recovery of fluorescence occurs on anaerobiosis. Use of mutants with defects in the ATP synthase or the respiratory chain show that quenching of fluorescence may be energized either by ATP hydrolysis or by substrate oxidation through the respiratory chain. Permeabilization of the outer membrane by treatment of intact cells with EDTA, or use of a mutant with an outer membrane permeable to lipophilic substances, results in a more rapid binding of NPN and in a decrease in quenching observed on substrate addition. NPN binds rapidly to everted membrane vesicles, but does not respond to membrane energization. It is proposed that inner membrane energization in intact cells alters the binding or environment of NPN in the outer membrane. The fluorescence recovery which occurs on anaerobiosis has two components. One component represents a reversal of the changes which occur on membrane energization. The other component of the fluorescence change is insensitive to the uncoupler CCCP and resembles the behaviour of NPN with everted membrane vesicles. It is suggested that a portion of the fluorescence events seen with NPN involves a response of the probe to changes in the inner membrane. 相似文献