全文获取类型
收费全文 | 214篇 |
免费 | 50篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 10篇 |
2014年 | 5篇 |
2013年 | 15篇 |
2012年 | 10篇 |
2011年 | 8篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 13篇 |
2007年 | 13篇 |
2006年 | 10篇 |
2005年 | 10篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1949年 | 3篇 |
1915年 | 1篇 |
1914年 | 1篇 |
1912年 | 1篇 |
1907年 | 1篇 |
1905年 | 1篇 |
1874年 | 1篇 |
排序方式: 共有264条查询结果,搜索用时 15 毫秒
1.
Elastase-like enzymes in human neutrophils localized by ultrastructural cytochemistry 总被引:6,自引:1,他引:5
The thiol ester N-t-Boc-L-alanine-p-nitrothiophenyl ester (Boc-Ala-SNp) was synthesized and applied as an ultrastructural cytochemical substrate for intracellular elastase-like enzymes. Mature human neutrophils incubated with Boc-Ala-SNp and gold ions generate an electron-dense reaction product, gold p-nitrothiophenolate, which is found in the nuclear membrane, Golgi complex, endoplasmic reticulum, mitochondria, and granules of these cells. Enzyme activity against Boc- Ala-SNp is also observed in developing monkey bone marrow neutrophils and in other blood cells. The intracellular neutrophil enzyme activity is elastase-like because it is characterized by a slightly alkaline pH optimum and is inactivated by exposure of the cells to general and specific active site inhibitors of neutrophil elastase. This substrate appears to have important potential for use in ultrastructural studies of intracellular elastase-like enzymes. 相似文献
2.
3.
J M Aiken F D Miller F Hagen D I McKenzie S A Krawetz J H van de Sande J B Rattner G H Dixon 《Biochemistry》1985,24(22):6268-6276
We have located an extensive (AC)n-rich but specific sequence downstream of three rainbow trout protamine genes. Although sharing considerable sequence homology, including a perfectly conserved 46 base pair repeat, the sequences exhibit a regular heterogeneity in the length of the (AC)n-rich tracts. Radioimmunoassay experiments, S1 nuclease sensitivity studies, two-dimensional electrophoretic analysis, and immunoelectron microscopy studies have been used to determine if the region could assume a Z DNA conformation. It was found that, in a supercoiled plasmid, the (AC)n-rich region has the ability to attain the Z DNA conformation under physiological conditions. 相似文献
4.
Dissolved organic carbon (DOC) in Lake Fryxell, 10 streams flowing into the lake, and the moat surrounding the lake was studied to determine the influence of sources and biogeochemical processes on its distribution and chemical nature. Lake Fryxell is an amictic, permanently ice-covered lake in the McMurdo Dry Valleys which contains benthic and planktonic microbial populations, but receives essentially no input of organic material from the ahumic soils of the watershed. Biological activity in the water column does not appear to influence the DOC depth profile, which is similar to the profiles for conservative inorganic constituents. DOC values for the streams varied with biomass in the stream channel, and ranged from 0.2 to 9.7 mg C/L. Fulvic acids in the streams were a lower percentage of the total DOC than in the lake. These samples contain recent carbon and appear to be simpler mixtures of compounds than the lake samples, indicating that they have undergone less humification. The fulvic acids from just above the sediments of the lake have a high sulfur content and are highly aliphatic. The main transformations occurring as these fractions diffuse upward in the water column are 1) loss of sulfur groups through the oxycline and 2) decrease in aliphatic carbon and increase in the heterogeneity of aliphatic moieties. The fraction of modem14C content of the lake fulvic acids range from a minimum of 0.68 (approximately 3000 years old) at 15m depth to 0.997 (recent material) just under the ice. The major processes controlling the DOC in the lake appear to be: 1) The transport of organic matter by the inflow streams resulting in the addition of recent organic material to the moat and upper waters of the lake; 2) The diffusion of organic matter composed of relict organic material and organic carbon resulting from the degradation of algae and bacteria from the bottom waters or sediments of the lake into overlying glacial melt water, 3) The addition of recent organic matter to the bottom waters of the lake from the moat. 相似文献
5.
6.
6-keto-prostaglandin E1 is not equipotent to prostacyclin (PGI2) as an antiaggregatory agent 总被引:5,自引:0,他引:5
A direct comparison of the relative potencies of the two antiaggregatory prostaglandins PGI2 and 6-keto-PGE1 showed PGI2 was at least 20 times more potent than 6-keto-PGE1 when tested against ADP-induced human platelet aggregation. This marked difference in potency was even more evident when the ability of PGI2 and 6-keto-PGI2 to stimulate platelet cyclic AMP levels was determined. When cyclic AMP levels were measured direct comparisons were difficult because the respective dose response curves were not parallel, but 10 ng of PGI2 was equivalent to 300 ng of 6-keto-PGE1. PGI2 was also more potent (10-20 times) than 6-keto-PGE1 as a disaggregatory agent, and the disaggregatory activity of both prostaglandins was enhanced by the phosphodiesterase inhibitor 1-methyl-3-isobutylmethylxanthine. PGI2 was also more active than 6-keto-PGE1 as an inhibitor of thrombus formation in dog coronary arteries in vivo. In vivo, 6-keto-PGE1 was at least 10 times less potent thatn PGI2, the exact difference could not be determined because 6-keto-PGE1 caused significant falls in blood pressure before anti-platelet activity could be detected. PGI2 is an intrinsically more potent anti-aggregatory molecule than 6-keto-PGE1, but these data do not rule out the possibility that some of the activities attributed to PGI2 could be the result of the conversin of PGI2 and/or 6-keto-PGF1 alpha to 6-keto-PGE1. 相似文献
7.
Experiments with anesthetized cats were done to study possible roles of different prostaglandins (PGs) in modulating sympathetic neuroeffector transmission. We recorded contractions of the nictitating membrane (n.m.), blood flow in the carotid artery, heart rate and blood pressure, both under control conditions and while stimulating the cut cervical sympathetic nerve. Intra-carotid arterial injection (i.a.) of PGD2 depressed sympathetic transmission to the n.m. without depressing the effects of exogenous norepinephrine (NE). In contrast, PGE2 enhanced the effects of nerve transmission or exogenous NE on the stimulated n.m. PGI2 had similar but shorter effects to PGE2. PGF2α or a stable PGH2 analog, contracted the n.m. smooth muscle with no detected effect on nerve transmission. Carotid blood flow was increased by PGD2, PGE2 and PGI2. PGD2 and PGI2 caused bradycardia that could be blocked by atropine. This ability of PGD2 to modulate autonomic nerve activity is of particular interest because of recent reports that nerve tissue synthesizes PGD2. 相似文献
8.
O.V. Miller J.W. Aiken R.J. Shebuski R.R. Gorman 《Prostaglandins & other lipid mediators》1980,20(2):391-400
A direct comparison of the relative potencies of the two anti-aggregatory prostaglandins PGI2 and 6-keto-PGE1 showed PGI2 was at least 20 times more potent than 6-keto-PGE1 when tested against ADP-induced human platelet aggregation. This marked difference in potency was even more evident when the ability of PGI2 and 6-keto-PGE1 to stimulate platelet cyclic AMP levels was determined. When cyclic AMP levels were measured direct comparisons were difficult because the respective dose response curves were not parallel, but 10 ng of PGI2 was equivalent to 300 ng of 6-keto-PGE1.PGI2 was also more potent (10–20 times) than 6-keto-PGE1 as a disaggregatory agent, and the disaggregatory activity of both prostaglandins was enhanced by the phosphodiesterase inhibitor 1-methyl-3-isobutylmethylxanthine.PGI2 was also more active than 6-keto-PGE1 as an inhibitor of thrombus formation in dog coronary arteries in vivo. In vivo, 6-keto-PGE1 was at least 10 times less potent than PGI2, the exact difference could not be determined because 6-keto-PGE1 caused significant falls in blood pressure before anti-platelet activity could be detected.PGI2 is an intrinsically more potent anti-aggregatory molecule than 6-keto-PGE1, but these data do not rule out the possibility that some of the activities attributed to PGI2 could be the result of the conversion of PGI2 and/or 6-keto-PGF1α to 6-keto-PGE1. 相似文献
9.
J M Clark B M Aiken D W Vaughan H M Kagan 《The journal of histochemistry and cytochemistry》1980,28(1):90-92
The thiol ester, N-t-butyloxycarbonyl-L-alanine-p-nitrothiophenyl ester (Boc-Ala-SNp) has been synthesized and applied as an ultrastructural cytochemical substrate for leukocytic elastase-like enzymes. Incubation of fixed human neutrophils with Boc-Ala-SNp in the presence of gold ions generates electron-dense deposits of gold p-nitrothiophenolate in the nuclear membrane, endoplasmic reticulum, Golgi complex, mitochondria, and granules. Deposition of product is inhibited by pretreatment of cells with general and specific chemical inactivators of neutrophil elastase. This substrate appears to have significant potential as a probe for the ultrastructural localization of elastase-like activity. 相似文献
10.
Ron Aiken 《Hydrobiologia》1981,76(1-2):11-12
Female Palmacorixa nana showed clear preference for wood oviposition substrates over Elodea and plexiglass in both laboratory and field experiments. Wood was chosen because of its rigidity and rough surface. These data raise the possibility that males could gain access to females by controlling localized resources.Present address: Department 0f Entomology University 0f Alberta Edmonton, Alberta, Canada T6 G 2E3Present address: Department 0f Entomology University 0f Alberta Edmonton, Alberta, Canada T6 G 2E3 相似文献