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91.
Active transport of -aminoisobutyric acid (AIB) in Vibrio costicola utilizes a system with affinity for glycine, alanine and, to some extent, methionine. AIB transport was more tolerant of high salt concentrations (3–4 M NaCl) in cells grown in the presence of 1.0 M NaCl than in those grown in the presence of 0.5 M NaCl. The former cells could also maintain much higher ATP contents than the latter in high salt concentrations.Transport kinetic studies performed with bacteria grown in 1.0 M NaCl revealed three effects of the Na+ ion: the first effect is to increase the apparent affinity (K
t) of the transport system for AIB at Na+ concentrations <0.2 M, the second to increase the maximum velocity (V
max) of transport (Na+ concentrations between 0.2 and 1.0 M), and the third to decrease the V
max without affectig K
t (Na+ concentrations >1.0 M). Cells grown in the presence of 0.5 M or 1.0 M NaCl had similar affinity for AIV. Thus, the differences in salt response of transport in these cells do not seem due to differences in AIB binding. Large, transport-inhibitory concentrations of NaCl resulted in efflux of AIB from cells preloaded in 0.5 M or 1.0 M NaCl, with most dramatic efflux occurring from the cells whose AIB transport was more salt-sensitive. Our results suggest that the degree to which high salt concentrations affect the transmembrane electrochemical energy source used for transport and ATP synthesis is an important determinant of salt tolerance.Abbreviations AIB
-aminoisobutyric acid
- pmf
proton motive force 相似文献
92.
Eric Jakobsson 《Journal of mathematical biology》1978,6(3):235-248
Summary The axon membrane is simulated by standard Hodgkin-Huxley leakage and potassium channels plus a coupled transient excited
state kinetic scheme for the sodium channel. This scheme for the sodium channel is as proposed previously by the author. Simultations
are presented showing the form of the action potential, threshold behavior, accommodation, and repetitive firing. It is seen
that the form of the individual action potential, its all-or-none nature, and its refractory period are well simulated by
this model, as they are by the standard Hodgkin-Huxley model. However, the model differs markedly from the Hodgkin-Huxley
model with respect to repetitive firing and accommodation to stimulating currents of slowly rising intensity, in ways that
are anomn to be related to those features of the sodium inactivation which are anomalous to the H-H model. The tendency for
repetitive firing is highly dependent on that parameter which primarily determintes the existence of the inactivation shift
in voltage clamp experiments, in such a way that the more pronounced the inactivation shift, the less the tendency for repetitive
firing,. The tendency for accommodation is highly dependent on that parameter which primarily determines the “τc − τh” separation, in such a way that the greater the separation the greater the tendency for the membrane to accommodate without
firing action potentials to a slowly rising current. 相似文献
93.
M Sugano T Ide H Okamatsu H Takahara 《Biochemical and biophysical research communications》1977,79(4):1092-1097
A method was developed for the determination of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in the microsomal fraction of crypt cells and villi of rat intestinal mucosa. Addition of trypsin inhibitor to homogenizing and incubation media at a proper concentration appeared inevitable for measurement of the activity of the villi fraction. The reductase in crypt cells was also slightly enhanced by the addition of the inhibitor. Using this technique, the enzyme activity in villi was found to be as active as the crypt cell fraction. Since other types of protease inhibitors were not necessarily effective, it was suggested that specific enzyme(s) inactivates the mucosal reductase in the course of measurement. 相似文献
94.
Summary Recently, antibiotics have enjoyed widespread usage as tools in studies of epithelial transport. In the present study we assess the usefulness of the pore-forming antibiotic gramicidin D as a means for probing the electrical properties of the tight epithelium rabbit urinary bladder. Addition of 50 M gramicidin to the mucosal bath (either a NaCl or KCl Ringer's solution) led to a large irreversible increase in the transepithelial conductance (G
T
) within 800 sec.G
T
increased by approximately 1200% and 500% in KCl and NaCl Ringer's solutions, respectively. Microelectrode measurements of the resistance ration (the ration of apical membrane resitance to basolateral membrane resistance) showed that apical membrane resistance is dereased by the drug. Measurements of the basolateral membrane resistance (R
bl
) and tight junctional resistance (R
j
) using a new and independent method (based on the perturbation of basolateral membrane electrogenic Na+ pump) demonstrated thatR
bl
andR
j
were unaffected, suggesting that the effects of gramicidin are restricted to the apical membrane for periods of at least 2 hours after drug addition. The selectivity of the gramicidin-induced permeability in the apical membrane was calculated from measurements of the apical membrane potential after ion substitutions using a modified version of the constant field equation. The selectivity sequence for cations was Cs+>K+>Na+>Li+>choline. Unlike the commonly used polyene antibiotics nystatin and amphotericin B, gramicidin did not induce a significant Cl– permeability. In addition, the dose-response curve had a slope of 1. A method is described for calculating membrane resistances directly from transepithelial measurements under some conditions of gramicidin use, without requiring the use of microlectrode measurements. 相似文献
95.
Microsporidian spore polypeptides separated with sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) can be used to identify isolates of microsporidia. The spore polypeptides separated with SDS/PAGE provided unique, reproducible electrophoretic profiles which were not influenced by host species or the temperature at which the host larvae were maintained for development. Furthermore, host proteins were not detected in electrophoretic profiles of the spore polypeptides. Spore mixtures of two microsporidian species can be detected when the spore polypeptides of either or both species have been previously separated with SDS/PAGE. 相似文献
96.
Erich Kessler 《Archives of microbiology》1977,113(1-2):139-141
Five physiological and biochemical characters, which had proved to be valuable for the taxonomy of the genus Chlorella, were studied in the genus Prototheca. There is no hydrogenase activity and no liquefaction of gelatin. Most strains are very acidtolerant (limit of growth at pH 2.0 or 2.5) and very salt-tolerant (limit of growth at 4 or 5% NaCl). Two strains grow well at 38°C. The 16 strains, which were previously assigned to seven taxa, fall into four different groups. Our results tend to support the assumption that Prototheca might be related to Chlorella protothecoides. 相似文献
97.
Vanessa M. Hutchings 《Planta》1978,138(3):237-241
In Ricinus cotyledons, evidence for proton extrusion came from observation of direct acidification of the medium in the presence of potassium salts. Increasing K+ influx with increasing pH suggested a link between K+ influx and H+ efflux by an H+ pump. The kinetics of K+ influx and H+ efflux were consistent with a 1:1 stoichiometry K+:H+, which may indicate either electrical coupling or carrier mediated exchange. The results were consistent with an H+ pump setting up an electrochemical potential gradient which provides the driving force for an H+-sucrose cotransport and the movement of K+. With reference to this, a model for phloem loading is suggested. 相似文献
98.
99.
Ghosts derived from bovine chromaffin granules have a 32Pi-ATP exchange activity which is associated with the H+ pump of that membrane. This activity was low when compared to bacteria, chloroplasts or submitochondrial particles, but had similar properties (Km for ATP and Pi, ATP/Mg2+ ratio, pH profile, inhibition by dicyclohexylcarbodiimide and tributyltin) to the ATPase from above membranes. The 32Pi-ATP exchange activity was solubilized by cholate/octylglucoside mixtures. The soluble extract was lipid depleted by ammonium sulfate fractionation and partially purified by sucrose gradient centrifugation. The purified preparation was reconstituted with phospholipids by freeze-thawing. The reconstituted vesicles had a 32Pi-ATP exchange sensitive to dicyclohexylcarbodiimide and trybutyltin and an ATPase with a sensitivity to the inhibitors which varied with the reconstitution conditions. The α- and β-subunits of F1-ATPase were major components of the preparation. 相似文献
100.
Specific binding of radiolabeled L-glutamic acid (Glu) was examined using rat brain synaptic membranes treated with a low concentration of Triton X-100. The binding drastically increased in proportion to increasing concentrations of the detergent used up to 0.1%. Addition of 100 mM sodium acetate significantly potentiated the binding in membranes not treated with Triton X-100, whereas it markedly inhibited the binding in Triton-treated membranes. The binding in Triton-treated membranes was inversely dependent on incubation temperature and reached a plateau within 10 min after the initiation of incubation at 2 degrees C, whereas the time required to attain equilibrium at 30 degrees C was less than 1 min. Sodium acetate invariably inhibited the binding detected at both temperatures independently of the incubation time via decreasing the affinity for the ligand. The binding was significantly displaced by agonists and antagonists for an N-methyl-D-aspartate (NMDA)-sensitive subclass of brain excitatory amino acid receptors, but not by those for the other subclasses. Inclusion of sodium acetate reduced the potencies of NMDA agonists to displace the binding without virtually affecting those of NMDA antagonists. Moreover, sodium ions inhibited the ability of Glu to potentiate the binding of N-[3H] [1-(2-thienyl)cyclohexyl]piperidine to open NMDA channels in Triton-treated membranes. These results suggest that sodium ions may play an additional modulatory role in the termination process of neurotransmission mediated by excitatory amino acids via facilitating a transformation of the NMDA recognition site from a state with high affinity for agonists to a state with low affinity. 相似文献