全文获取类型
收费全文 | 1583篇 |
免费 | 140篇 |
出版年
2023年 | 11篇 |
2022年 | 12篇 |
2021年 | 25篇 |
2020年 | 13篇 |
2019年 | 19篇 |
2018年 | 12篇 |
2017年 | 19篇 |
2016年 | 35篇 |
2015年 | 59篇 |
2014年 | 50篇 |
2013年 | 83篇 |
2012年 | 103篇 |
2011年 | 126篇 |
2010年 | 72篇 |
2009年 | 60篇 |
2008年 | 104篇 |
2007年 | 96篇 |
2006年 | 99篇 |
2005年 | 88篇 |
2004年 | 83篇 |
2003年 | 104篇 |
2002年 | 86篇 |
2001年 | 15篇 |
2000年 | 8篇 |
1999年 | 16篇 |
1998年 | 19篇 |
1997年 | 18篇 |
1996年 | 9篇 |
1995年 | 14篇 |
1994年 | 18篇 |
1993年 | 24篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 12篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 23篇 |
1982年 | 20篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1975年 | 7篇 |
1973年 | 5篇 |
1970年 | 6篇 |
排序方式: 共有1723条查询结果,搜索用时 15 毫秒
61.
Chanjuan Guo Judy Simon Rainer Gasche Pascale Sarah Naumann Carolin Bimüller Rodica Pena Andrea Polle Ingrid Kögel-Knabner Bernd Zeller Heinz Rennenberg Michael Dannenmann 《Plant and Soil》2013,369(1-2):657-668
Aims
Our aims were to characterize the fate of leaf-litter-derived nitrogen in the plant-soil-microbe system of a temperate beech forest of Southern Germany and to identify its importance for N nutrition of beech seedlings.Methods
15N-labelled leaf litter was traced in situ into abiotic and biotic N pools in mineral soil as well as into beech seedlings and mycorrhizal root tips over three growing seasons.Results
There was a rapid transfer of 15N into the mineral soil already 21 days after tracer application with soil microbial biomass initially representing the dominant litter-N sink. However, 15N recovery in non-extractable soil N pools strongly increased over time and subsequently became the dominant 15N sink. Recovery in plant biomass accounted for only 0.025 % of 15N excess after 876 days. After three growing seasons, 15N excess recovery was characterized by the following sequence: non-extractable soil N?>>?extractable soil N including microbial biomass?>>?plant biomass?>?ectomycorrhizal root tips.Conclusions
After quick vertical dislocation and cycling through microbial N pools, there was a rapid stabilization of leaf-litter-derived N in non-extractable N pools of the mineral soil. Very low 15N recovery in beech seedlings suggests a high importance of other N sources such as root litter for N nutrition of beech understorey. 相似文献62.
Chanjuan Guo Michael Dannenmann Rainer Gasche Bernd Zeller Hans Papen Andrea Polle Heinz Rennenberg Judy Simon 《Plant and Soil》2013,368(1-2):519-534
Background and aims
Litter decomposition is regulated by e.g. substrate quality and environmental factors, particularly water availability. The partitioning of nutrients released from litter between vegetation and soil microorganisms may, therefore, be affected by changing climate. This study aimed to elucidate the impact of litter type and drought on the fate of litter-derived N in beech seedlings and soil microbes.Methods
We quantified 15N recovery rates in plant and soil N pools by adding 15N-labelled leaf and/or root litter under controlled conditions.Results
Root litter was favoured over leaf litter for N acquisition by beech seedlings and soil microorganisms. Drought reduced 15N recovery from litter in seedlings thereby affecting root N nutrition. 15N accumulated in seedlings in different sinks depending on litter type.Conclusions
Root turnover appears to influence (a) N availability in the soil for plants and soil microbes and (b) N acquisition and retention despite a presumably extremely dynamic turnover of microbial biomass. Compared to soil microorganisms, beech seedlings represent a very minor short-term N sink, despite a potentially high N residence time. Furthermore, soil microbes constitute a significant N pool that can be released in the long term and, thus, may become available for N nutrition of plants. 相似文献63.
Plant LOSS OF GDU 2 (LOG2) and Mammalian Mahogunin Ring Finger 1 (MGRN1) proteins are RING-type E3 ligases sharing similarity N-terminal to the RING domain. Deletion of this region disrupts the interaction of LOG2 with the plant membrane protein GLUTAMINE DUMPER1 (GDU1). Phylogenetic analysis identified two clades of LOG2/MGRN1-like proteins in vertebrates and plants. The ability of MGRN1 to functionally replace LOG2 was tested. MGRN1 ubiquitylates GDU1 in vitro and can partially substitute for LOG2 in the plant, partially restoring amino acid resistance to a GDU1-myc over-expression, log2-2 background. Altogether, these results suggest a conserved function for the N-terminal domain in evolution. 相似文献
64.
65.
Respiratory complex II (succinate:ubiquinone oxidoreductase) connects the tricarboxylic acid cycle to the electron transport chain in mitochondria and many prokaryotes. Complex II mutations have been linked to neurodegenerative diseases and metabolic defects in cancer. However, there is no convenient stoichiometric assay for the catalytic activity of complex II. Here, we present a simple, quantitative, real-time method to detect the production of fumarate from succinate by complex II that is easy to implement and applicable to the isolated enzyme, membrane preparations, and tissue homogenates. Our assay uses fumarate hydratase to convert fumarate to malate and uses oxaloacetate decarboxylating malic dehydrogenase to convert malate to pyruvate and to convert NADP+ to NADPH; the NADPH is detected spectrometrically. Simple protocols for the high-yield production of the two enzymes required are described; oxaloacetate decarboxylating malic dehydrogenase is also suitable for accurate determination of the activity of fumarate hydratase. Unlike existing spectrometric assay methods for complex II that rely on artificial electron acceptors (e.g., 2,6-dichlorophenolindophenol), our coupled assay is specific and stoichiometric (1:1 for succinate oxidation to NADPH formation), so it is suitable for comprehensive analyses of the catalysis and inhibition of succinate dehydrogenase activities in samples with both simple and complex compositions. 相似文献
66.
Himabindu Reddy Seerapu Susmita Borthakur Nathan Kong Sudesh Agrawal Judy Drazba Amit Vasanji Alessandro Fantin Christiana Ruhrberg Matthias Buck Arie Horowitz 《FEBS letters》2013
Though the vascular endothelial growth factor coreceptor neuropilin-1 (Nrp1) plays a critical role in vascular development, its precise function is not fully understood. We identified a group of novel binding partners of the cytoplasmic domain of Nrp1 that includes the focal adhesion regulator, Filamin A (FlnA). Endothelial cells (ECs) expressing a Nrp1 mutant devoid of the cytoplasmic domain (nrp1cytoΔ/Δ) migrated significantly slower in response to VEGF relative to the cells expressing wild-type Nrp1 (nrp1+/+ cells). The rate of FA turnover in VEGF-treated nrp1cytoΔ/Δ ECs was an order of magnitude lower in comparison to nrp1+/+ ECs, thus accounting for the slower migration rate of the nrp1cytoΔ/Δ ECs. 相似文献
67.
68.
69.
Adriaan M. Dokter Judy Shamoun-Baranes Michael U. Kemp Sander Tijm Iwan Holleman 《PloS one》2013,8(1)
At temperate latitudes the synoptic patterns of bird migration are strongly structured by the presence of cyclones and anticyclones, both in the horizontal and altitudinal dimensions. In certain synoptic conditions, birds may efficiently cross regions with opposing surface wind by choosing a higher flight altitude with more favourable wind. We observed migratory passerines at mid-latitudes that selected high altitude wind optima on particular nights, leading to the formation of structured migration layers at varying altitude up to 3 km. Using long-term vertical profiling of bird migration by C-band Doppler radar in the Netherlands, we find that such migration layers occur nearly exclusively during spring migration in the presence of a high-pressure system. A conceptual analytic framework providing insight into the synoptic patterns of wind assistance for migrants that includes the altitudinal dimension has so far been lacking. We present a simple model for a baroclinic atmosphere that relates vertical profiles of wind assistance to the pressure and temperature patterns occurring at temperate latitudes. We show how the magnitude and direction of the large scale horizontal temperature gradient affects the relative gain in wind assistance that migrants obtain through ascending. Temperature gradients typical for northerly high-pressure systems in spring are shown to cause high altitude wind optima in the easterly sectors of anticyclones, thereby explaining the frequent observations of high altitude migration in these synoptic conditions. Given the recurring synoptic arrangements of pressure systems across temperate continents, the opportunities for exploiting high altitude wind will differ between flyways, for example between easterly and westerly oceanic coasts. 相似文献
70.
Brian Huntley Judy R. M. Allen Yvonne C. Collingham Thomas Hickler Adrian M. Lister Joy Singarayer Anthony J. Stuart Martin T. Sykes Paul J. Valdes 《PloS one》2013,8(4)
Whereas fossil evidence indicates extensive treeless vegetation and diverse grazing megafauna in Europe and northern Asia during the last glacial, experiments combining vegetation models and climate models have to-date simulated widespread persistence of trees. Resolving this conflict is key to understanding both last glacial ecosystems and extinction of most of the mega-herbivores. Using a dynamic vegetation model (DVM) we explored the implications of the differing climatic conditions generated by a general circulation model (GCM) in “normal” and “hosing” experiments. Whilst the former approximate interstadial conditions, the latter, designed to mimic Heinrich Events, approximate stadial conditions. The “hosing” experiments gave simulated European vegetation much closer in composition to that inferred from fossil evidence than did the “normal” experiments. Given the short duration of interstadials, and the rate at which forest cover expanded during the late-glacial and early Holocene, our results demonstrate the importance of millennial variability in determining the character of last glacial ecosystems. 相似文献