全文获取类型
收费全文 | 116篇 |
免费 | 0篇 |
国内免费 | 4篇 |
专业分类
系统科学 | 1篇 |
教育与普及 | 1篇 |
理论与方法论 | 3篇 |
现状及发展 | 60篇 |
研究方法 | 5篇 |
综合类 | 49篇 |
自然研究 | 1篇 |
出版年
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 13篇 |
2010年 | 5篇 |
2009年 | 3篇 |
2008年 | 11篇 |
2007年 | 7篇 |
2006年 | 2篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2002年 | 5篇 |
1996年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1967年 | 2篇 |
排序方式: 共有120条查询结果,搜索用时 93 毫秒
11.
Biogenically driven organic contribution to marine aerosol 总被引:1,自引:0,他引:1
O'Dowd CD Facchini MC Cavalli F Ceburnis D Mircea M Decesari S Fuzzi S Yoon YJ Putaud JP 《Nature》2004,431(7009):676-680
Marine aerosol contributes significantly to the global aerosol load and consequently has an important impact on both the Earth's albedo and climate. So far, much of the focus on marine aerosol has centred on the production of aerosol from sea-salt and non-sea-salt sulphates. Recent field experiments, however, have shown that known aerosol production processes for inorganic species cannot account for the entire aerosol mass that occurs in submicrometre sizes. Several experimental studies have pointed to the presence of significant concentrations of organic matter in marine aerosol. There is some information available about the composition of organic matter, but the contribution of organic matter to marine aerosol, as a function of aerosol size, as well as its characterization as hydrophilic or hydrophobic, has been lacking. Here we measure the physical and chemical characteristics of submicrometre marine aerosol over the North Atlantic Ocean during plankton blooms progressing from spring through to autumn. We find that during bloom periods, the organic fraction dominates and contributes 63% to the submicrometre aerosol mass (about 45% is water-insoluble and about 18% water-soluble). In winter, when biological activity is at its lowest, the organic fraction decreases to 15%. Our model simulations indicate that organic matter can enhance the cloud droplet concentration by 15% to more than 100% and is therefore an important component of the aerosol-cloud-climate feedback system involving marine biota. 相似文献
12.
Absence of S6K1 protects against age- and diet-induced obesity while enhancing insulin sensitivity 总被引:1,自引:0,他引:1
Um SH Frigerio F Watanabe M Picard F Joaquin M Sticker M Fumagalli S Allegrini PR Kozma SC Auwerx J Thomas G 《Nature》2004,431(7005):200-205
Elucidating the signalling mechanisms by which obesity leads to impaired insulin action is critical in the development of therapeutic strategies for the treatment of diabetes. Recently, mice deficient for S6 Kinase 1 (S6K1), an effector of the mammalian target of rapamycin (mTOR) that acts to integrate nutrient and insulin signals, were shown to be hypoinsulinaemic, glucose intolerant and have reduced beta-cell mass. However, S6K1-deficient mice maintain normal glucose levels during fasting, suggesting hypersensitivity to insulin, raising the question of their metabolic fate as a function of age and diet. Here, we report that S6K1-deficient mice are protected against obesity owing to enhanced beta-oxidation. However on a high fat diet, levels of glucose and free fatty acids still rise in S6K1-deficient mice, resulting in insulin receptor desensitization. Nevertheless, S6K1-deficient mice remain sensitive to insulin owing to the apparent loss of a negative feedback loop from S6K1 to insulin receptor substrate 1 (IRS1), which blunts S307 and S636/S639 phosphorylation; sites involved in insulin resistance. Moreover, wild-type mice on a high fat diet as well as K/K A(y) and ob/ob (also known as Lep/Lep) mice-two genetic models of obesity-have markedly elevated S6K1 activity and, unlike S6K1-deficient mice, increased phosphorylation of IRS1 S307 and S636/S639. Thus under conditions of nutrient satiation S6K1 negatively regulates insulin signalling. 相似文献
13.
Ceci M Gaviraghi C Gorrini C Sala LA Offenhäuser N Marchisio PC Biffo S 《Nature》2003,426(6966):579-584
The assembly of 80S ribosomes requires joining of the 40S and 60S subunits, which is triggered by the formation of an initiation complex on the 40S subunit. This event is rate-limiting for translation, and depends on external stimuli and the status of the cell. Here we show that 60S subunits are activated by release of eIF6 (also termed p27BBP). In the cytoplasm, eIF6 is bound to free 60S but not to 80S. Furthermore, eIF6 interacts in the cytoplasm with RACK1, a receptor for activated protein kinase C (PKC). RACK1 is a major component of translating ribosomes, which harbour significant amounts of PKC. Loading 60S subunits with eIF6 caused a dose-dependent translational block and impairment of 80S formation, which were reversed by expression of RACK1 and stimulation of PKC in vivo and in vitro. PKC stimulation led to eIF6 phosphorylation, and mutation of a serine residue in the carboxy terminus of eIF6 impaired RACK1/PKC-mediated translational rescue. We propose that eIF6 release regulates subunit joining, and that RACK1 provides a physical and functional link between PKC signalling and ribosome activation. 相似文献
14.
G. Cimino S. De Rosa S. De Stefano G. Sodano 《Cellular and molecular life sciences : CMLS》1985,41(10):1335-1336
Summary Polygodial (1), the defense metabolite stored in the skin of the nudibranchDendrodoris limbata, is toxic for the mollusc itself when injected into the hepatopancreas. Biosynthetic experiments using labeled mevalonic acid were devised to investigate a possible metabolic relationship between1 and the mixture of sesquiterpenoidic esters2, stored in the hepatopancreas. The results suggest that1 and2 are biosynthesized by independent pathways.Thanks are due to G. Villani for supplyingDendrodoris limbata and to A. Trabucco for technical assistance. 相似文献
15.
Reduced K-means (RKM) and Factorial K-means (FKM) are two data reduction techniques incorporating principal component analysis and K-means into a unified methodology to obtain a reduced set of components for variables and an optimal partition for objects.
RKM finds clusters in a reduced space by maximizing the between-clusters deviance without imposing any condition on the within-clusters
deviance, so that clusters are isolated but they might be heterogeneous. On the other hand, FKM identifies clusters in a reduced
space by minimizing the within-clusters deviance without imposing any condition on the between-clusters deviance. Thus, clusters
are homogeneous, but they might not be isolated. The two techniques give different results because the total deviance in the
reduced space for the two methodologies is not constant; hence the minimization of the within-clusters deviance is not equivalent
to the maximization of the between-clusters deviance. In this paper a modification of the two techniques is introduced to
avoid the afore mentioned weaknesses. It is shown that the two modified methods give the same results, thus merging RKM and
FKM into a new methodology. It is called Factor Discriminant K-means (FDKM), because it combines Linear Discriminant Analysis and K-means. The paper examines several theoretical properties of FDKM and its performances with a simulation study. An application
on real-world data is presented to show the features of FDKM. 相似文献
16.
Summary The levels of serotonin, dopamine and norepinephrine exhibit seasonal changes in the central nervous system of Mytilus edulis. These monoamines were higher during the summer and lower during the winter. 相似文献
17.
18.
19.
J. E. Haley G. B. Stefano E. J. Catapane 《Cellular and molecular life sciences : CMLS》1978,34(2):210-212
Summary These studies have demonstrated a positive correlation between the acidic phospholipids and the serotonin content and between the lysolecithin and the dopamine content in the cerebral, pedal and visceral ganglia ofMytilus edulis. These relationships were further supported by experiments utilizing 6-hydroxydopamine and 5,6-dihydroxytryptamine.This study was partially supported by USPHS grant NS 10845 to Dr E. Aiello of Fordham University.Presently at Medgar Evers College of C.U.N.Y., Brooklyn, N.Y. 11225. 相似文献
20.