全文获取类型
收费全文 | 301篇 |
免费 | 22篇 |
国内免费 | 1篇 |
出版年
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 22篇 |
2012年 | 19篇 |
2011年 | 12篇 |
2010年 | 10篇 |
2009年 | 6篇 |
2008年 | 10篇 |
2007年 | 19篇 |
2006年 | 10篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1969年 | 2篇 |
1962年 | 2篇 |
1953年 | 2篇 |
1938年 | 1篇 |
排序方式: 共有324条查询结果,搜索用时 15 毫秒
51.
van den Berg MA Albang R Albermann K Badger JH Daran JM Driessen AJ Garcia-Estrada C Fedorova ND Harris DM Heijne WH Joardar V Kiel JA Kovalchuk A Martín JF Nierman WC Nijland JG Pronk JT Roubos JA van der Klei IJ van Peij NN Veenhuis M von Döhren H Wagner C Wortman J Bovenberg RA 《Nature biotechnology》2008,26(10):1161-1168
52.
Kaj Sand-Jensen 《Hydrobiologia》2008,610(1):307-319
Swift flow in streams may physically influence the morphology and distribution of plants. I quantified drag as a function
of velocity, biomass and their interaction on the trailing canopy of seven European stream species in an experimental flume
and evaluated its importance for species distribution. Drag increased at a power of 1.3–1.9 with velocity and 0.59–0.77 with
biomass in 75% of the measurements. Velocity and biomass interacted because higher velocity causes reconfiguration and greater
internal shelter to unimpeded flow and higher biomass enhances shelter among neighbouring shoots. Increase of drag with velocity
did not differ systematically among inherently streamlined or non-streamlined species while increase of drag with biomass
was smallest among non-streamlined shoots which provide greater mutual shelter. At low shoot density, inherently streamlined
species usually experienced the lowest drag conducive to colonisation and growth in swift flow. At high shoot density, no
systematic differences in drag existed between the two morphologies. No clear relationship existed between drag forces, morphology
and field distribution of species as a function of current velocity probably because a variety of environmental conditions
and plant traits influences distribution. Drag on the trailing canopy usually increased 15- to 35-fold for a 100-fold increase
of biomass suggesting that an even distribution of plants at low density across the stream bed offers greater resistance to
downstream flow than an uneven distribution with the same biomass confined to dense patches surrounded by open flow channels.
Thus, management strategies to ensure a patchy plants distribution should be suitable for combining agricultural drainage
and ecological stream quality.
Handling editor: S. M. Thomaz 相似文献
53.
54.
? Lobelia dortmanna thrives in oligotrophic, softwater lakes thanks to O(2) and CO(2) exchange across roots and uptake of sediment nutrients. We hypothesize that low gas permeability of leaves constrains Lobelia to pristine habitats because plants go anoxic in the dark if O(2) vanishes from sediments. ? We added organic matter to sediments and followed O(2) dynamics in plants and sediments using microelectrodes. To investigate plant stress, nutrient content and photosynthetic capacity of leaves were measured. ? Small additions of organic matter triggered O(2) depletion and accumulation of NH(4)(+), Fe(2+) and CO(2) in sediments. O(2) in leaf lacunae fluctuated from above air saturation in the light to anoxia late in the dark in natural sediments, but organic enrichment prolonged anoxia because of higher O(2) consumption and restricted uptake from the water. Leaf N and P dropped below minimum thresholds for cell function in enriched sediments and was accompanied by critically low chlorophyll and photosynthesis. ? We propose that anoxic stress restricts ATP formation and constrains transfer of nutrients to leaves. Brief anoxia in sediments and leaf lacunae late at night is a recurring summer phenomenon in Lobelia populations, but increased input of organic matter prolongs anoxia and reduces survival. 相似文献
55.
Ohrfelt A Zetterberg H Andersson K Persson R Secic D Brinkmalm G Wallin A Mulugeta E Francis PT Vanmechelen E Aarsland D Ballard C Blennow K Westman-Brinkmalm A 《Neurochemical research》2011,36(11):2029-2042
Parkinson's disease (PD) and Dementia with Lewy bodies (DLB) are neurodegenerative diseases that are characterized by intra-neuronal inclusions of Lewy bodies in distinct brain regions. These inclusions consist mainly of aggregated α-synuclein (α-syn) protein. The present study used immunoprecipitation combined with nanoflow liquid chromatography (LC) coupled to high resolution electrospray ionization Fourier transform ion cyclotron resonance tandem mass spectrometry (ESI-FTICR-MS/MS) to determine known and novel isoforms of α-syn in brain tissue homogenates. N-terminally acetylated full-length α-syn (Ac-α-syn?????) and two N-terminally acetylated C-terminally truncated forms of α-syn (Ac-α-syn????? and Ac-α-syn?????) were found. The different forms of α-syn were further studied by Western blotting in brain tissue homogenates from the temporal cortex Brodmann area 36 (BA36) and the dorsolateral prefrontal cortex BA9 derived from controls, patients with DLB and PD with dementia (PDD). Quantification of α-syn in each brain tissue fraction was performed using a novel enzyme-linked immunosorbent assay (ELISA). 相似文献
56.
Ann Brinkmalm Gunnar Brinkmalm William G. Honer Julie A. Moreno Joel Jakobsson Giovanna R. Mallucci Henrik Zetterberg Kaj Blennow Annika ?hrfelt 《Molecular & cellular proteomics : MCP》2014,13(10):2584-2592
We report a novel strategy for studying synaptic pathology by concurrently measuring levels of four SNARE complex proteins from individual brain tissue samples. This method combines affinity purification and mass spectrometry and can be applied directly for studies of SNARE complex proteins in multiple species or modified to target other key elements in neuronal function. We use the technique to demonstrate altered levels of presynaptic proteins in Alzheimer disease patients and prion-infected mice.One prominent pathological feature of neuropsychiatric disorders such as Alzheimer disease (AD)1 is severe synaptic loss (1–3). Previous reports of AD patients have shown that presynaptic dysfunction might occur early in the disease process (1, 4). Cortical synapse pathology has also been shown to correlate to the severity of dementia more closely than other pathological hallmarks of AD such as plaques and neurofibrillary tangles (5, 6). The SNARE proteins are essential components for the regulation of neurotransmitter exocytosis at the presynaptic site (7). Animal models suggest that changed expression or modification of SNARE complex proteins (synaptosomal-associated protein 25 (SNAP-25), syntaxin-1, and vesicle-associated membrane protein (VAMP)) alters synaptic function and is an interesting target for the development of therapeutics for neuropsychiatric illness (8, 9). The constituents of the SNARE complex are either localized in synaptic vesicles (VAMPs) or anchored at the presynaptic plasma membrane (SNAP-25 and syntaxin). The SNARE proteins are tightly assembled, and subsequent neurotransmitter release of the complex is quickly dissociated by N-ethylmaleimide-sensitive factor (7, 10–12). Because they are both strongly associated into complexes and membrane associated, the SNARE proteins are difficult to analyze via mass spectrometry, which is incompatible with most detergents necessary for the solubilization of proteins. Each SNARE complex protein exists in several isoforms that are differently distributed within the central nervous system (13–18). Post-translational modifications and truncated variants of the SNARE proteins make investigation of the protein expression even more complicated.In this study we developed an approach for the characterization and concurrent quantification of SNARE complex proteins that combines affinity purification by immunoprecipitation and mass spectrometry (IP-MS). We used precipitation with monoclonal antibodies against SNAP-25 to target the SNARE complex proteins and nanoflow LC–tandem mass spectrometry (LC-MS/MS) to characterize the co-immunoprecipitated interaction partners. Selected reaction monitoring (SRM) on a triple quadrupole mass spectrometer coupled to a microflow LC system was used for quantification of the SNARE proteins. To demonstrate the usability of the IP-MS method, we performed a comparison of SNARE complex protein levels in brain tissue from AD patients and age-matched controls, as well as a study of SNARE complex protein levels in brain tissue from prion-infected mice. 相似文献
57.
The little auk population of the Thule district in Greenland is generally believed to be the largest anywhere and to comprise
more than half of the world population, although published numbers have largely been conjectural. In 1996/1997 we estimated
breeding density of little auks at Hakluyt Island in this district by colour-marking a number of birds in three study plots
and subsequently counting marked and unmarked birds present in the plots. The density estimate considered most representative
of the colony was 1.8 birds/m2 or 0.73 pairs/m2 (±7%). From surveys of the inhabitated area of the scree slopes, this density implies a total little auk population for the
island of 130,000 pairs. An extrapolation to the entire Thule district suggests a population in the area of at least 15 million
pairs, which is in general agreement with previously published assumptions.
Accepted: 3 January 2000 相似文献
58.
Madeleine Zetterberg Annica Sjölander Malin von Otter Mona Seibt Palmér Sara Landgren Lennart Minthon Anders Wallin Niels Andreasen Kaj Blennow Henrik Zetterberg 《Molecular neurodegeneration》2010,5(1):1-5
Alzheimer's disease (AD) is characterized by protein aggregates, i.e. senile plaques and neurofibrillary tangles. The ubiquitin-proteasome system has been proposed a role in proteolytic removal of these protein aggregates. Ubiquitin carboxy-terminal hydrolase L1 (UCHL1) is a de-ubiquitinating enzyme with important functions in recycling of ubiquitin. The S18Y polymorphism of the UCHL1 gene confers protection against Parkinson's disease. In this study, the genotype and allele frequencies of the UCHL1 S18Y polymorphism were investigated in 452 AD patients and 234 control subjects, recruited from four memory clinics in Sweden. Using a binary logistic regression model including UCHL1 allele A and APOE ε4 allele positivity, age and sex as covariates with AD diagnosis as dependent variable, an adjusted OR of 0.82 ([95% CI 0.55-1.24], P = 0.35) was obtained for a positive UCHL1 allele A carrier status. The present study thus do not support a protective effect of the UCHL1 S18Y polymorphism against AD. 相似文献
59.
60.
Morphological – anatomical features of the terrestrial and the aquatic life form of the rosette species Littorella uniflora, inhabiting nutrient poor soils of oligotrophic lakes, were investigated together with growth rates of both life forms and of transplants. Growth rates were the same for the two life forms. However, growth of transplanted plants was somewhat reduced by transition from one environment to another. This was especially true for aquatic plants, which may be stressed by desiccation when moved to the terrestrial environment. The morphological – anatomical differences between the life forms were small compared with many other amphibious species which produce highly specialized leaves and life forms in air and under water. It is suggested that the conservative leaf morphology of Littorella is a consequence of the high dependence on rhizospheric CO2 of both the aquatic and the terrestrial form of Littorella, making production of leaves specialized for carbon uptake in one specific environment unnecessary. 相似文献