全文获取类型
收费全文 | 202篇 |
免费 | 20篇 |
出版年
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 10篇 |
2014年 | 6篇 |
2013年 | 6篇 |
2012年 | 8篇 |
2011年 | 9篇 |
2010年 | 4篇 |
2009年 | 12篇 |
2008年 | 10篇 |
2007年 | 6篇 |
2006年 | 4篇 |
2005年 | 2篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 11篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有222条查询结果,搜索用时 15 毫秒
1.
2.
3.
Effects of low-chloride solutions on action potentials of sheep cadiac purkinje fibers 总被引:2,自引:0,他引:2 下载免费PDF全文
The rapid repolarization during phase 1 of the action potential of sheep cardiac purkinje fibers has been attributed to a time- and voltage-dependent chloride current. In part, this conclusion was based on experiments that showed a substantial slowing of phase 1 when larger, presumably impermeant, anions were substituted for chloride in tyrode’s solution. We have re- examined the electrical effects of low-chloride solutions. We recorded action potentials of sheep cardiac purkinje fibers in normal tyrode’s solution and in low-chloride solutions made by substituting sodium propionate, acetylglycinate, methylsulfate, or methanesulfonate for the NaCl of Tyrode’s solution. Total calcium was adjusted to keep calcium ion activity of test solutions equal to that of control solutions. Propionate gave qualitatively variable results in preliminary experiments; it was not tested further. Low-chloride solutions made with the other anions gave much more consistent results: phase 1 and the notch that often occurs between phases 1 and 2 were usually unaffected, and the action potential duration usually increased. The only apparent change in the resting potential was a transient 3-6 mV depolarization when low-chloride solution was first admitted to the chamber, and a symmetrical transient hyperpolarization when chloride was returned to normal. If a time- and voltage-dependent chloride current exists in sheep cardiac purkinje fibers, our results suggest that it plays little role in generating phase 1 of the action potential. 相似文献
4.
5.
6.
Plasminogen activator and collagenase production by cultured capillary endothelial cells 总被引:33,自引:17,他引:16 下载免费PDF全文
Cultured bovine capillary endothelial (BCE) cells produce low levels of collagenolytic activity and significant amounts of the serine protease plasminogen activator (PA). When grown in the presence of nanomolar quantities of the tumor promoter 12-O-tetradecanoyl phorbol-13-acetate (TPA), BCE cells produced 5-15 times more collagenolytic activity and 2-10 times more PA than untreated cells. The enhanced production of these enzymes was dependent on the dose of TPA used, with maximal response at 10(-7) to 10(-8) M. Phorbol didecanoate (PDD), an analog of TPA which is an active tumor promoter, also increased protease production. 4-O-methyl-TPA and 4α-PDD, two analogs of TPA which are inactive as tumor promoters, had no effect on protease production. Increased PA and collagenase activities were detected within 7.5 and 19 h, respectively, after the addition of TPA. The TPA-stimulated BCE cells synthesized a urokinase-type PA and a typical vertebrate collagenase. BCE cells were compared with bovine aortic endothelial (BAE) cells and bovine embryonic skin (BES) fibroblasts with respect to their production of protease in response to TPA. Under normal growth conditions, low levels of collagenolyic activity were detected in the culture fluids from BCE, BAE, and BES cells. BCE cells produced 5-13 times the basal levels of collagenolytic activity in response to TPA, whereas BAE cells and BES fibroblasts showed a minimal response to TPA. Both BCE and BAE cells exhibited relatively high basal levels of PA, the production of which was stimulated approximately threefold by the addition of TPA. The observation that BCE cells and not BAE cells produced high levels of both PA and collagenase activities in response to TPA demonstrates a significant difference between these two types of endothelial cells and suggests that the enhanced detectable activities are a property unique to bovine capillary and microvessel and endothelial cells. 相似文献
7.
AB Kane RP Stanton EG Raymond ME Dobson ME Knafelc JL Farber 《The Journal of cell biology》1980,87(3):643-651
The relationship between intracellular lysosomal rupture and cell death caused by silica was studied in P388d(1) macrophages. After 3 h of exposure to 150 μg silica in medium containing 1.8 mM Ca(2+), 60 percent of the cells were unable to exclude trypan blue. In the absence of extracellular Ca(2+), however, all of the cells remained viable. Phagocytosis of silica particles occurred to the same extent in the presence or absence of Ca(2+). The percentage of P388D(1) cells killed by silica depended on the dose and the concentration of Ca(2+) in the medium. Intracellular lyosomal rupture after exposure to silica was measured by acridine orange fluorescence or histochemical assay of horseradish peroxidase. With either assay, 60 percent of the cells exposed to 150 μg silica for 3 h in the presence of Ca(2+) showed intracellular lysosomal rupture, was not associated with measureable degradation of total DNA, RNA, protein, or phospholipids or accelerated turnover of exogenous horseradish peroxidase. Pretreatment with promethazine (20 μg/ml) protected 80 percent of P388D(1) macrophages against silica toxicity although lysosomal rupture occurred in 60-70 percent of the cells. Intracellular lysosomal rupture was prevented in 80 percent of the cells by pretreatment with indomethacin (5 x 10(-5)M), yet 40-50 percent of the cells died after 3 h of exposure to 150 μg silica in 1.8 mM extracellular Ca(2+). The calcium ionophore A23187 also caused intracellular lysosomal rupture in 90-98 percent of the cells treated for 1 h in either the presence or absence of extracellular Ca(2+). With the addition of 1.8 mM Ca(2+), 80 percent of the cells was killed after 3 h, whereas all of the cells remained viable in the absence of Ca(2+). These experiments suggest that intracellular lysosomal rupture is not causally related to the cell death cause by silica or . Cell death is dependent on extracellular Ca(2+) and may be mediated by an influx of these ions across the plasma membrane permeability barrier damaged directly by exposure to these toxins. A23187相似文献
8.
9.
Sonia Cabezas Martina Carrete José L. Tella Tracy A. Marchant Gary R. Bortolotti 《Biological invasions》2013,15(3):521-527
Current avian invasions are often the result of exotic birds accidentally escaping from cages. It has been hypothesised that the higher invasiveness of wild-caught cage-birds compared to captive-bred ones could be related to the loss of ability in captive-bred birds to cope with new environments. The acute stress response plays an important role in how animals cope with challenges because elevated corticosterone (CORT) levels can mediate learning and memory consolidation and help to increase their survival prospects. We experimentally tested whether exotic wild-caught and captive-bred cage-birds differ in their responses to acute stress using a representative sample of parrots. Wild-caught individuals showed longer CORT responses to acute stress than captive-bred ones, both at inter- and intra-specific levels when comparing wild-birds to the first generation born in captivity. Captive-bred birds may have attenuated their CORT responses due to acclimation, while high mortality rates during the international trade of wild-caught birds could have selected those individuals that are better able to cope with stress. We suggest that the longer acute response found in wild-caught parrots could help them to escape from cages and survive when facing challenges in new wild environments, possibly contributing to their higher invasiveness. 相似文献
10.
Tella JL Bortolotti GR Dawson RD Forero MG 《Proceedings. Biological sciences / The Royal Society》2000,267(1446):891-895
Life-history theory predicts that parents face a trade-off between the number and viability of the progeny they produce. We found evidence for an apparent trade-off in a free-living population of American kestrels (Falco sparverius), as larger clutches produced more but lighter fledglings. However, while the body mass of fledglings has traditionally been used as a measure of survival prospect, offspring immunocompetence should also play an important role. We thus measured the T-cell-mediated immune response of fledgling kestrels in relation to brood traits and nest-rearing conditions through a cross-fostering experiment. The immune response was positively correlated with the body condition of fledglings, but was also higher in those hatched from five-egg than four-egg clutches. These results were not influenced by other brood traits, nor by current exposure to stressors and infectious agents, as measured by serological variables. Such ability to resist pathogens may account for why the probability of offspring returning to the study area in subsequent years, when controlling for brood size, was higher for five-egg than four-egg clutches. These results suggest an optimal clutch size through maternal effects on offspring immunocompetence rather than a trade-off between the number and quality of the offspring. 相似文献