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81.
Both NaCl and NaF promoted PGE2 binding to epididymal adipocyte membranes by apparent increase in the binding affinity. In order to distinguish between the effect of fluoride and the ‘salt effect’ of sodium on PGE2 binding, the effects of Mg2+ and guanyl nucleotides on PGE2 binding in the presence of NaCl or NaF were compared. Mg2+ decreased PGE2 binding; high NaF concentration abolished this inhibition, while increased NaCl concentratipns did not affect the Mg2+ inhibition. In the presence of Mg2+ the effects of NaCl and NaF were additive. The enhancement of PGE2 binding by fluoride, unlike sodium, was dependent on the presence of Mg2+. Induction of the membranes with GDPβS, Gpp(NH)p, GTP or GTPγS increased PGE, binding. Gradual increase in NaF concentrations in the presence of guanyl nucleotides resulted in stimulation of PGE2 binding at low NaF concentrations and inhibition of PGE2 binding at higjh NaF concentrations. No changes in the stimulatory action of NaCl on PGE2 binding were observed in the simulatenous presence of NaCl and guanyl nucleotides. A biphasic effect on PGE2 binding was observed with a wide concentration range of guanyl nucleotides. Treatment of the isolated membranes with cholera or pertussis toxins stimulated the adenylyl cyclase activity of the membranes, but failed to influence PGE2 binding. The implications of these findings are discussed. 相似文献
82.
G protein-coupled signaling is utilized by a wide variety of eukaryotes for communicating information from the extracellular environment. Signal termination is achieved by the action of the arrestins, which bind to activated, phosphorylated G protein-coupled receptors. We describe here crystallographic studies of visual arrestin in its basal conformation. The salient features of the structure are a bipartite molecule with an unusual polar core. This core is stabilized in part by an extended carboxy-terminal tail that locks the molecule into an inactive state. In addition, arrestin is found to be a dimer of two asymmetric molecules, suggesting an intrinsic conformational plasticity. In conjunction with biochemical and mutagenesis data, we propose a molecular mechanism by which arrestin is activated for receptor binding. 相似文献
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Interactions between polynucleotides and platinum (II) complexes 总被引:1,自引:0,他引:1
S Wherland E Deutsch J Eliason P B Sigler 《Biochemical and biophysical research communications》1973,54(2):662-668
Reaction of either or Pt(NH3)2Cl2 with poly(A) in dilute aqueous solution leads to quantitative precipitation of the polymer at Pt/nucleotide ratios above 0.5. It is proposed that at ratios less than this, intramolecular binding of one Pt to two bases is favored; at higher ratios, intermolecular cross-linking becomes important and precipitation results. The absence of isomer selectivity in precipitation implies that the biological specificity of the form results from a process other than cross-linking of polynucleotide strands. Other observations suggest that the coordinated ammonia of nucleotide-platinum(II) ammine complexes may be unusually labile. 相似文献
86.
Factors affecting the outcome of the acidification power test of yeast quality: Critical reappraisal
Brewery bottom yeast strain 95 from the Pilsner Urquell propagation unit was used to reappraise the efficiency of the acidification power (AP) test consisting in determining the spontaneous (oxygen-induced) and glucose-induced medium acidification caused by yeast and lactic acid bacteria under standard conditions, and used widely for assessing and predicting the vitality of industrial strains. AP was evaluated in yeast stored for different periods of time (0-28 d) at 4 degrees C, at different temperatures before and during the test (0-55 degrees C), and at different concentrations of cells and glucose and different cells-to-glucose ratios. All these factors had a strong effect on acidification kinetics and the AP value. By contrast, the duration of the lag period between yeast collection and the test (0-6 h) had no perceptible effect on the AP value. The best results were achieved at saturation concentrations of cells (> 10 g pressed yeast or approximately 14 g yeast slurry per 100 mL) and glucose (approximately 3 %) and at 25 degrees C. Since an exact evaluation of acidification characteristics depends strongly on the kinetics of the process, the AP test should include monitoring the time course of the acidification. 相似文献
87.
We have developed a novel screening method that measures the kinetics and potencies of inhibitors of the yeast multidrug resistance pumps Pdr5p and Snq2p. The assay uses the potentiometric fluorescent probe diS-C3(3) (as a benchmark substrate of both pumps) to distinguish drugs with minimal effects on plasma membrane potential as a marker of side-effects on membrane function and integrity. Using FK506, its structural analog rapamycin and enniatin B, we showed that our assay can also be used to determine the minimum drug concentration causing an immediate inhibitory effect and to compare the inhibitory potencies of the drug on the two pumps. We found that the protonophore CCCP effectively inhibits the transport of diS-C3(3) by both pumps and confirmed the activation of membrane H+-ATPase by CCCP. 相似文献
88.
Glycosides of benzodioxole-indole alkaloid 6-hydroxy-galanthindole (7-(6′-(hydroxymethyl)benzo[d][1′,3′]dioxol-5′-yl)-1-methyl-1H-indol-6-ol) having axial chirality were isolated from Narcissus cultivar ‘Dutch Master’. The structure, including absolute configuration, was determined by means of extensive spectroscopic data such as UV, IR, CD, MS, 1D and 2D NMR spectra, and computational chiroptical methods. The aglycone has a structure containing two aromatic moieties with substituents hindering rotation about the biaryl axis and is connected to a saccharide moiety linked at C-6 and made up of one, two, or three sugars (glucose, α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranose, and trisaccharide ([β-d-xylopyranosyl(1 → 2)]-[α-l-rhamnopyranosyl-(1 → 6)]-β-d-glucopyranose). 相似文献
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KK Chan B Dassanayake R Deen RE Wickramarachchi SK Kumarage S Samita KI Deen 《World journal of surgical oncology》2010,8(1):1-11