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351.
Marked stimulation of glucagon release and modest stimulation of insulin release were observed during in situ perfusion of the rat pancreas with AVP or OT. Glucagon release in response to AVP or OT (200 pg/ml) gradually increased over a 45 min perfusion period reaching maxima of 500% and 300% of the pre-stimulatory levels, respectively. Insulin release transiently increased by 100%. In each case release rates returned to control values immediately after withdrawal of the peptides. Total glucagon release was concentration dependent and linear from 20 pg to 20 ng AVP or OT/ml (r greater than .97). Pancreatic response to DDAVP perfused at 20 ng/ml was virtually indistinguishable from that induced by AVP at 200 pg/ml. This demonstration of a glucagonotrophic action of the neurohypophysial hormones in the in situ perfused rat pancreas confirms earlier studies using isolated islets and bolus IV injection. 相似文献
352.
353.
354.
Y Shimohigashi J W Dunning A J Kolar C H Stammer 《International journal of peptide and protein research》1983,21(2):202-208
Two kinds of dehydropeptide analogs of enkephalin containing a delta Tyr unit at the N-terminus have been synthesized by coupling Boc-delta Tyr-(Cl2 Bzl)-OH with amino acid amides and tetrapeptide esters using the water soluble carbodiimide-HOBt method. Pentapeptides consisting of delta Tyr1, and delta Phe4 or delta Leu5 were also prepared. Ultraviolet difference spectroscopy was important in the characterization of the dehydro moieties, delta Tyr, delta Phe and delta Leu. Attempts to liberate delta Tyr1-enkephalins have been unsuccessful because of the instability of an N-terminal delta Tyr residue having p-phenolic group in the side chain. 相似文献
355.
Anahita Z. Mostafavi Donovan K. Lujan Katelyn M. Erickson Christina D. Martinez Jerry M. Troutman 《Bioorganic & medicinal chemistry》2013,21(17):5428-5435
Undecaprenyl Pyrophosphate Synthase (UPPS) is an enzyme critical to the production of complex polysaccharides in bacteria, as it produces the crucial bactoprenol scaffold on which these materials are assembled. Methods to characterize the systems associated with polysaccharide production are non-trivial, in part due to the lack of chemical tools to investigate their assembly. In this report, we develop a new fluorescent tool using UPPS to incorporate a powerful fluorescent anthranilamide moiety into bactoprenol. The activity of this analogue in polysaccharide biosynthesis is then tested with the initiating hexose-1-phosphate transferases involved in Capsular Polysaccharide A biosynthesis in the symbiont Bacteroides fragilis and the asparagine-linked glycosylation system of the pathogenic Campylobacter jejuni. In addition, it is shown that the UPPS used to make this probe is not specific for E-configured isoprenoid substrates and that elongation by UPPS is required for activity with the downstream enzymes. 相似文献
356.
357.
Jamie Dunning Antony W. Diamond Stephen E. Christmas Emma-Louise Cole Rebecca L. Holberton Hannah J. Jackson 《Bird Study》2013,60(4):570-573
We report the discovery of photoluminescence in the ornamental bill of the Atlantic Puffin Fratercula arctica. The excitation and emission properties of the ceres of one dead and three live individuals were similar. 相似文献
358.
Chronic exposure of pancreatic islets to sulfonylureas
(SUs) is known to impair the ability of islets
to respond to subsequent acute stimulation by
SUs or glucose. Nateglinide (NAT) is a novel
insulinotropic agent with a primarily site of action
at β-cell KATP channels, which is common to the
structurally diverse drugs like repaglinide (REP)
and the SUs. Earlier studies on the kinetics, glucosedependence
and sensitivity to metabolic inhibitors
of the interaction between NAT and KATP channels
suggested a distinct signaling pathways with NAT
compared to REP, glyburide (GLY) or glimepiride
(GLI). To obtain further evidence for this concept,
the present study compared the insulin secretion in
vitro from rat islets stimulated acutely by NAT, GLY,
GLI or REP at equipotent concentrations during 1-hr
static incubation following overnight treatment
with GLY or tolbutamide (TOL). The islets fully
retained the responsiveness to NAT stimulation
after prolonged pretreatment with both SUs, while
their acute response to REP, GLY, and GLI was
markedly attenuated, confirming the desensitization
of islets. The insulinotropic efficacy of NAT in islets
desensitized to SUs may result from a distinct
receptor/effector mechanism, which contributes to
the unique pharmacological profile of NAT. 相似文献
359.