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41.
Preincubation of brain membranes with phospholipase A2 (PLA2) has been shown previously to affect the binding characteristics of various recognition sites associated with the gamma-aminobutyric acid (GABA) receptor complex. In the present study, we have investigated the effects of PLA2 (from Naja naja siamensis venom) on the functional activity of the GABA receptor/chloride ion channel. PLA2 (0.001-0.02 U/mg protein) preincubation decreased pentobarbital-induced 36Cl- efflux and muscimol-induced 36Cl- uptake in rat cerebral cortical synaptoneurosomes. The effect of PLA2 was prevented by EGTA and two nonselective PLA2 inhibitors, mepacrine and bromophenacyl bromide. The removal of free fatty acids by addition of bovine serum albumin both prevented and reversed the effect of PLA2. Products of the catalytic activity of PLA2, such as the unsaturated free fatty acids, arachidonic and oleic acids, mimicked the effect of PLA2. However, the saturated fatty acid, palmitic acid, and lysophosphatidyl choline had no effect on pentobarbital-induced 36Cl- efflux. Because unsaturated free fatty acids are highly susceptible to peroxidation by oxygen radicals, the role of oxygen radicals was investigated. Xanthine plus xanthine oxidase, a superoxide radical generating system, mimicked the effect of PLA2, whereas the superoxide radical scavenger, superoxide dismutase, diminished the effects of PLA2 and arachidonic acid on pentobarbital-induced 36Cl- efflux. Similarly, the effect of PLA2 was also inhibited by methanol (1 mM), a scavenger of the hydroxyl radical, and by catalase. These data indicate that exogenously added PLA2 induces alterations in membrane phospholipids, possibly promoting the generation of oxygen radicals and fatty acid peroxides which can ultimately modulate GABA/barbiturate receptor function in brain. 相似文献
42.
The biology of mycorrhiza in the Ericaceae 总被引:6,自引:4,他引:2
43.
44.
Oxygen and CO2 exchange were measured concurrently in leaves of shade-grownAlocasia macrorrhiza (L.) G. Don during lightflecks consisting of short periods of high photon flux density (PFD) superimposed on a low-PFD background illumination. Oxygen exchange was measured with a zirconium-oxide ceramic cell in an atmosphere containing 1 600 bar O2 and 350 bar CO2. Following an increase in PFD from 10 to 500 mol photons·m-2·s-1, O2 evolution immediately increased to a maximum rate that was about twice as high as the highest CO2-exchange rates that were observed. Oxygen evolution then decreased over the next 5–10 s to rates equal to the much more slowly increasing rates of CO2 uptake. When the PFD was decreased at the end of a lightfleck, O2 evolution decreased nearly instantaneously to the low-PFD rate while CO2 fixation continued at an elevated rate for about 20 s. When PFD during the lightfleck was at a level that was limiting for steady-state CO2 exchange, then the O2-evolution rate was constant during the lightfleck. This observed pattern of O2 evolution during lightflecks indicated that the maximum rate of electron transport exceeded the maximum rate of CO2 fixation in these leaves. In noninduced leaves, rates of O2 evolution for the first fraction of a second were about as high as rates in fully induced leaves, indicating that O2 evolution and the electron-transport chain are not directly affected by the leaf's induction state. Severalfold differences between induced and noninduced leaves in O2 evolution during a lightfleck were seen for lightflecks longer than a few seconds where the rate of O2 evolution appeared to be limited by the utilization of reducing power in CO2 fixation.Abbreviation PFD
photon flux density (of photosynthetically active radiation) 相似文献
45.
Hubert Felle 《Planta》1988,176(2):248-255
In cells of Zea mays (root hairs, coleoptiles) and Riccia fluitans (rhizoids, thalli) intracellular Ca2+ and pH have been measured with double-barrelled microelectrodes. Free Ca2+ activities of 109–187 nM (Riccia rhizoids), 94–160 nM (Riccia thalli), 145–231 nM (Zea root hairs), 84–143 nM (Zea coleoptiles) were found, and therefore identified as cytoplasmic. In a few cases (Riccia rhizoids), free Ca2+ was in the lower millimolar range (2.3±0.8 mM). A change in external Ca2+ from 0.1 to 10 mM caused an initial and short transient increase in cytoplasmic free Ca2+ which finally levelled off at about 0.2 pCa unit below the control, whereas in the presence of cyanide the Ca2+ activity returned to the control level. It is suggested that this behaviour is indicative of active cellular Ca2+ regulation, and since it is energy-dependent, may involve a Ca2+-ATPase. Acidification of the cytoplasmic pH and alkalinization of the vacuolar pH lead to a simultaneous increase in cytoplasmic free Ca2+, while alkalinization of pHc decreased the Ca2+ activity. Since this is true for such remote organisms as Riccia and Zea, it may be concluded that regulation of cytoplasmic pH and free Ca2+ are interrelated. It is further concluded that double-barrelled microelectrodes are useful tools for investigations of intracellular ion activities in plant cells.Symbols and abbreviations m, m
membrane potential difference, changes thereof
- PVC
polyvinylchloride 相似文献
46.
Richard C. Woodman John T. Curnutte Bernard M. Babior 《Free radical biology & medicine》1988,5(5-6):355-361
We examined the effects of the recombinant human colony stimulating factors GM-CSF and G-CSF, cycloheximide (a protein synthesis inhibitor) and dihydrocytochalasin B (a microfilament disrupting agent) upon FMLP (N-formyl-methionyl-leucylphenylalanine)-stimulated O2 − production by neutrophils. We confirmed a time dependent augmentation of O2 − production following preincubation of neutrophils either alone or with colony stimulating factors. Furthermore, we found that GM-CSF, but not G-CSF, increased O2 − production at some concentrations of the stimulus. Preincubation of neutrophils with cycloheximide in the absence of CSF caused a marked fall in O2−-production that was first evident at 2 hours. The fall in O2−-forming capacity caused by cycloheximide was much less pronounced if dihydrocytochalasin B was also included in the preincubation buffer. These findings suggest a previously unrecognized role for de novo protein synthesis in maintaining the ability of neutrophils to manufacture O2−, and support earlier studies indicating that the cycling of FMLP receptors between the cell membrane and an intracellular compartment is important in determining the magnitude of the respiratory burst in FMLP-stimulated neutrophils. 相似文献
47.
The mechanism of the vanadate (V(v))-dependent oxidation of NADH was different in phosphate buffers and in phosphate-free media. In phosphate-free media (aqueous medium or HEPES buffer) the vanadyl (V(v)) generated by the direct V(v)-dependent oxidation of NADH formed a complex with V(v). In phosphate buffers V(v) autoxidized instead of forming a complex with V(v). The generated superoxide radical (O2−) initiated, in turn, a high-rate free radical chain oxidation of NADH. Phosphate did not stimulate the V(v)-dependent NADH oxidation catalyzed by O2−-generating systems. Monovanadate proved to be a stronger catalyzer of NADH oxidation as compared to polyvanadate. 相似文献
48.
Robert E. Beyer 《Free radical biology & medicine》1988,5(5-6):297-303
The ability of coenzyme Q to inhibit lipid peroxidation in intact animals as well as in mitochondrial, submitochondrial, and microsomal systems has been tested. Rats fed coenzyme Q prior to being treated with carbon tetrachloride or while being treated with ethanol excrete less thiobarbituric acid-reacting material in the urine than such rats not fed coenzyme Q. Liver homogenates, mitochondria, and microsomes isolated from rats treated with carbon tetrachloride and ethanol catalyze lipid peroxidation at rates which exceed those from animals also fed coenzyme Q. The rate of lipid peroxidation catalyzed by submitochondrial particles isolated from hearts of young, old, and endurance trained elderly rats was inversely proportional to the coenzyme Q content of the submitochondrial preparation in assays in which succinate was employed to reduce the endogenous coenzyme Q. Reduced, but not oxidized, coenzyme Q inhibited lipid peroxidation catalyzed by rat liver microsomal preparations. These results provide additional evidence in support of an antioxidant role for coenzyme Q. 相似文献
49.
G. K. Innes B. J. Fuller K. E. F. Hobbs 《In vitro cellular & developmental biology. Plant》1988,24(2):126-132
Summary Rat hepatocytes were isolated and then maintained in serum-free cell culture medium for 24 h. The amount of malondialdehyde
(MDA) accumulated in the medium was assayed and used as a measure of lipid peroxidation. The acivity of lactate dehydrogenase
(LDH) and urea were measured in the medium and used as indicators of hepatocellular viability and function. The effects of
iron; desferrioxamine mesylate (Desferal), an iron chelator; and mannitol, a hydroxyl free radical scavenger were investigated.
The addition of iron, Fe2 resulted in a three-fold increase in the levels of MDA. Desferal inhibited the production of MDA and blocked the effect of
Fe2+. Neither iron nor Desferal had any effect on LDH or urea levels. Mannitol had no effect on MDA or urea production, but caused
a 4 to 8-fold increase in the LDH levels in the medium. The results show that iron is involved in the mechanism of lipid peroxidation
in hepatocyte cultures but suggest that as a pathologic event lipid peroxidation is not expressed in terms of viability during
the first 24 h of hepatocyte culture. 相似文献
50.
Incubation of horse-heart oxymyoglobin or metmyoglobin with excess H2O2 causes formation of myoglobin(IV), followed by haem degradation. At the time when haem degradation is observed, hydroxyl radicals (.OH) can be detected in the reaction mixture by their ability to degrade the sugar deoxyribose. Detection of hydroxyl radicals can be decreased by transferrin or by OH scavengers (mannitol, arginine, phenylalanine) but not by urea. Neither transferrin nor any of these scavengers inhibit the haem degradation. It is concluded that intact oxymyoglobin or metmyoglobin molecules do not react with H2O2 to form OH detectable by deoxyribose, but that H2O2 eventually leads to release of iron ions from the proteins. These released iron ions can react to form OH outside the protein or close to its surface. Salicylate and the iron chelator desferrioxamine stabilize myoglobin and prevent haem degradation. The biological importance of OH generated using iron ions released from myoglobin by H2O2 is discussed in relation to myocardial reoxygenation injury. 相似文献