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Studies of proteins that inhibit tissue factor activity have generally been conducted using either an extracted tissue homogenate ("thromboplastin") or tissue factor protein reconstituted into phospholipid vesicles rather than with tissue factor expressed in cell membranes (its physiological environment). In the present study, a human fibroblast cell strain was used to evaluate the effects of lipoprotein associated coagulation inhibitor (LACI), placental anticoagulant protein (PAP), and apolipoprotein A-II (apo A-II) on human tissue factor in cell membranes. LACI was tested from 7.8 to 500 pmol/L on fibroblasts cultured at cell densities ranging from 3,500 to 9,925 cells/well, and caused a progressive inhibition of tissue factor activity. PAP was tested from 3.9 nmol/L to 1 mumol/L at cell densities ranging from 4,500 to 15,400 cells/well and caused up to 83% inhibition of tissue factor activity. Inhibition by these proteins appeared to be influenced by cell density as well as whether the cells were intact or disrupted. Apo A-II, up to 1 mumol/L, did not inhibit the tissue factor activity of intact or disrupted fibroblasts at any cell density examined even though it did inhibit the activity of tissue factor in phospholipid vesicles. Of these inhibitors of tissue factor-dependent activation of factor X, LACI was the most effective in suppressing the generation of factor Xa activity. The effects obtained with apo A-II are clearly dependent on the nature of the tissue factor preparation with which it is tested. The disparity between the inhibitory effect of apo A-II on the activity of tissue factor reconstituted into lipid vesicles and the absence of effect on the activity of tissue factor remaining in cell membranes serves to reemphasize the necessity of reexamining results obtained with model systems using as nearly physiological reagents as possible. 相似文献
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1. The electrophysiological properties of sensory neurons that mediate withdrawal reflexes of Aplysia can be modulated by a variety of neurotransmitters. We compared the known excitatory actions of serotonin (5-HT) with the actions of FMRFamide (Phe-Met-Arg-Phe-NH2) and myomodulin (Pro-Met-Ser-Met-Leu-Arg-Leu-NH2) on the durations of action potentials and excitability. In addition, with the use of voltage-clamp and pharmacological separation techniques, we characterized the membrane currents that were modulated by each of the three agents. 2. Application of 5-HT produced an increase in the duration of action potentials and an enhancement of excitability in somata of the tail sensory neurons. FMRFamide and myomodulin reversed these excitatory effects and decreased the duration of action potentials and excitability. These results indicated that FMRFamide and myomodulin exerted inhibitory effects on the electrophysiological properties of the sensory neurons. properties of the sensory neurons. 3. FMRFamide appeared to modulate three K+ currents. The first current, which was increased by FMRFamide, had properties closely resembling those of the S-K+ current (IK,S). These properties include slow activation, little inactivation, and relative insensitivity to the K+ channel blockers 4-aminopyridine (4-AP) and tetraethylammonium (TEA). The second current, which was reduced by FMRFamide, had kinetic and pharmacological properties similar to those of a component of the Ca(2+)-activated K+ current (IK,Ca). Finally, at large depolarizations, FMRFamide appeared to increase a third current that was attenuated by 4-AP, suggesting that FMRFamide also modulated the delayed or voltage-dependent K+ current (IK,V). 4. Myomodulin appeared to modulate two of the currents modulated by FMRFamide, because it increased both IK,S and IK,V. Unlike FMRFamide, however, myomodulin did not appear to modulate IK,Ca. 5. Arachidonic acid mimicked the modulation of IK,S, IK,Ca, and IK,V by FMRFamide. Because myomodulin did not modulate IK,Ca, it appears that a second messenger other than arachidonic acid or its metabolites mediates the modulatory effects of myomodulin. 6. These results indicate that both FMRFamide and myomodulin can inhibit the tail sensory neurons by increasing IK,S. FMRFamide, but not myomodulin, also reduces IK,Ca, which suggests that under some conditions FMRFamide may also have excitatory actions. Finally, these results suggest that the effects of FMRFamide and myomodulin may be mediated by different second-messenger systems. 相似文献
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M. N. Sawka Ph.D. R. G. Knowlton D. S. Miles J. B. Critz 《European journal of applied physiology》1979,41(2):93-99
Summary The purpose of this investigation was to quantitate post-competition lactate (LA) concentrations of swimmers during a competitive collegiate meet. Blood LA was measured by an enzymatic method on 23 subjects 5 min after each race event. The largest mean LA concentration of 25.7 mM/L was observed in swimmers after competing in the 200-yd individual medley. Swimmers in the 200-yd butterfly, back, breast and freestyle races had similar mean blood LA concentrations (ranging from 16.4 to 20.6 mM/L). Swimmers in the two longest events, the 500-yd and 1,000-yd free style races, had mean LA concentrations of 15.6 and 10.0 mM/L, respectively. To account for the effects of motivation, LA concentrations were measured following maximal effort noncompetitive 100 and 200-yd swims. LA concentrations were slightly greater in conjunction with faster performances for the competitive as compared to the noncompetitive 100 and 200-yd swims. 相似文献
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Myosin VIIA gene: heterogeneity of the mutations responsible for Usher syndrome type IB 总被引:8,自引:1,他引:8
Levy G; Levi-Acobas F; Blanchard S; Gerber S; Larget-Piet D; Chenal V; Liu XZ; Newton V; Steel KP; Brown SD; Munnich A; Kaplan J; Petit C; Weil D 《Human molecular genetics》1997,6(1):111-116
Usher syndrome is recognized as the most frequent cause of hereditary
deaf-blindness. Usher syndrome type I (USH1), the most severe form of the
disease, is characterized by profound congenital sensorineural deafness,
constant vestibular dysfunction, and retinitis pigmentosa of prepubertal
onset. This form is genetically heterogeneous and five loci (USH1A-E) have
been mapped thusfar. However, only the gene responsible for USH1 B (which
accounts for approximately 75% of USH1 cases) has been characterized. It
encodes a long-tailed unconventional myosin, myosin VIIA, with a predicted
2215 amino acid sequence. Primers covering the complete myosin VIIA coding
sequence as well as the 3' non coding sequence were designed, allowing
direct sequence analysis of each of the 48 coding exons and flanking splice
sites in seven patients affected by USH1. Four novel mutations were thereby
identified. The possibility should now be considered of a sequence-based
prenatal diagnosis in some of the families affected by this very severe
form of Usher syndrome.
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