全文获取类型
收费全文 | 685篇 |
免费 | 73篇 |
专业分类
758篇 |
出版年
2023年 | 9篇 |
2022年 | 6篇 |
2021年 | 19篇 |
2020年 | 15篇 |
2019年 | 14篇 |
2018年 | 17篇 |
2017年 | 19篇 |
2016年 | 28篇 |
2015年 | 47篇 |
2014年 | 41篇 |
2013年 | 66篇 |
2012年 | 67篇 |
2011年 | 63篇 |
2010年 | 42篇 |
2009年 | 34篇 |
2008年 | 44篇 |
2007年 | 45篇 |
2006年 | 31篇 |
2005年 | 28篇 |
2004年 | 30篇 |
2003年 | 26篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有758条查询结果,搜索用时 15 毫秒
91.
In this study, we investigated the kinetic and the magnitude of dehydrations on yeast plasma membrane (PM) modifications because this parameter is crucial to cell survival. Functional (permeability) and structural (morphology, ultrastructure, and distribution of the protein Sur7-GFP contained in sterol-rich membrane microdomains) PM modifications were investigated by confocal and electron microscopy after progressive (non-lethal) and rapid (lethal) hyperosmotic perturbations. Rapid cell dehydration induced the formation of many PM invaginations followed by membrane internalization of low sterol content PM regions with time. Permeabilization of the plasma membrane occurred during the rehydration stage because of inadequacies in the membrane surface and led to cell death. Progressive dehydration conducted to the formation of some big PM pleats without membrane internalization. It also led to the modification of the distribution of the Sur7-GFP microdomains, suggesting that a lateral rearrangement of membrane components occurred. This event is a function of time and is involved in the particular deformations of the PM during a progressive perturbation. The maintenance of the repartition of the microdomains during rapid perturbations consolidates this assumption. These findings highlight that the perturbation kinetic influences the evolution of the PM organization and indicate the crucial role of PM lateral reorganization in cell survival to hydric perturbations. 相似文献
92.
Summary The condensation of thymidine-5-monophosphate was carried out in the presence of imidazole in aqueous solutions at neutral pH. Formation of oligo-deoxyribonucleotides up to four units was observed. 相似文献
93.
94.
Disruption of diacylglycerol kinase delta (DGKD) associated with seizures in humans and mice 下载免费PDF全文
Leach NT Sun Y Michaud S Zheng Y Ligon KL Ligon AH Sander T Korf BR Lu W Harris DJ Gusella JF Maas RL Quade BJ Cole AJ Kelz MB Morton CC 《American journal of human genetics》2007,80(4):792-799
We report a female patient with a de novo balanced translocation, 46,X,t(X;2)(p11.2;q37)dn, who exhibits seizures, capillary abnormality, developmental delay, infantile hypotonia, and obesity. The 2q37 breakpoint observed in association with the seizure phenotype is of particular interest, because it lies near loci implicated in epilepsy in humans and mice. Fluorescence in situ hybridization mapping of the translocation breakpoints showed that no known genes are disrupted at Xp11.2, whereas diacylglycerol kinase delta (DGKD) is disrupted at 2q37. Expression studies in Drosophila and mouse suggest that DGKD is involved in central nervous system development and function. Electroencephalographic assessment of Dgkd mutant mice revealed abnormal epileptic discharges and electrographic seizures in three of six homozygotes. These findings implicate DGKD disruption by the t(X;2)(p11.2;q37)dn in the observed phenotype and support a more general role for DGKD in the etiology of seizures. 相似文献
95.
96.
Interspecific interactions can vary within and among populations and geographical locations, and this variation can influence
the nature of the interaction (e.g. mutualistic versus antagonistic) and its evolutionary stability. Globeflowers are exclusively
pollinated by flies whose larvae feed only on their seeds. Here we document geographical variability in costs and benefits
in globeflowers in sustaining their pollinating flies throughout the range of this arctic-alpine European plant over several
years. A total of 1,710 flower heads from 38 populations were analysed for their carpel, egg and seed contents. Individual
and population analyses control for the confounding influences of variation in both: (1) population traits, such as fly density
and egg distribution among flower heads; and (2) individuals traits, such as carpel and egg numbers per flower head. Despite
considerable variation in ecological conditions and pollinator densities across populations, large proportions (range 33–58%)
of seeds are released after predation, with a benefit-to-cost ratio of 3, indicating that the mutualism is stable over the
whole globeflower geographical range. The stability of the mutualistic interaction relies on density-dependent competition
among larvae co-developing in a flower head. This competition is revealed by a sharp decrease in the number of seeds eaten
per larva with increasing larval number, and is intensified by non-uniform egg distribution among globeflowers within a population.
Carpel number is highly variable across globeflowers (range 10–69), and flies lay more eggs in large flowers. Most plants
within a population contribute to the rearing of pollinators, but some pay more than others. Large globeflowers lose more
seed to pollinator larvae, but also release more seed than smaller plants. The apparent alignment of interests between fly
and plant (positive relationship between numbers of seeds released and destroyed) is shown to hide a conflict of interest
found when flower size is controlled for. 相似文献
97.
98.
Fuchs S Frenzel K Hubert C Lyng R Muller L Michaud A Xiao HD Adams JW Capecchi MR Corvol P Shur BD Bernstein KE 《Nature medicine》2005,11(11):1140-2; author reply 1142-3
99.
Parkinson's disease (PD) is a common age-related, progressive neurodegenerative disease of unknown etiology. Environmental factors have long been suspected to participate in the pathogenesis of PD due to the existence of neurotoxins that preferentially damage the dopaminergic nigrostriatal pathway. In the past few years, novel insights into the degenerative process have been provided by the discovery of genes responsible for rare monogenic parkinsonian syndromes. Compelling evidence is accumulating, suggesting that the products of several of these genes can interact with environmental toxins and intervene in molecular pathways controlling the functional integrity of mitochondria. 相似文献
100.
Harvesting the microalgae Phaeodactylum tricornutum with polyaluminum chloride, aluminium sulphate, chitosan and alkalinity-induced flocculation 总被引:1,自引:0,他引:1
Sema ?irin Rosa Trobajo Carles Ibanez Joan Salvadó 《Journal of applied phycology》2012,24(5):1067-1080
The purpose of this study was to explore efficient methods of harvesting the microalga Phaeodactylum tricornutum. Natural sedimentation experiments, performed at different light and temperature conditions, did not yield significant improvements in efficiency even after 1?week. When alkalinity-induced flocculation was performed, both the flocculation efficiency and the concentration factor dramatically improved at pH?=?9.75 (0.5–0.7 units over the original pH of the culture) after 10?min settling time. Sedimentation rates are documented at pH ranging between pH?9.75 and 11.0. The results of the application of two conventional flocculants used in wastewater treatment, polyaluminium chloride and aluminium sulphate, are also presented. Chitosan was also used as a natural flocculating agent to improve possible contamination problems in the downstream process. pH was adjusted in order to determine optimum flocculation efficiency of chitosan in combination with a high concentration factor. Satisfactory results were found with chitosan at an adjusted pH of 9.9 using concentrations as low as 20?mg?L?1, after testing a flocculant range of 5–200?mg?L?1. 相似文献