全文获取类型
收费全文 | 502篇 |
免费 | 51篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 4篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 12篇 |
2015年 | 22篇 |
2014年 | 26篇 |
2013年 | 25篇 |
2012年 | 25篇 |
2011年 | 38篇 |
2010年 | 20篇 |
2009年 | 22篇 |
2008年 | 42篇 |
2007年 | 40篇 |
2006年 | 23篇 |
2005年 | 23篇 |
2004年 | 23篇 |
2003年 | 16篇 |
2002年 | 24篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1969年 | 3篇 |
1968年 | 4篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1963年 | 2篇 |
1961年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有553条查询结果,搜索用时 31 毫秒
81.
The lumpy distribution of species along a continuous one-dimensional niche axis recently found by Scheffer and van Nes (Scheffer
and van Ness 2006) is explained mathematically. We show that it emerges simply from the eigenvalue and eigenvectors of the community matrix.
Both the transient patterns—lumps and gaps between them—as well as the asymptotic equilibrium are explained. If the species
are evenly distributed along the niche axis, the emergence of these patterns can be demonstrated analytically. The more general
case, of randomly distributed species, shows only slight deviations and is illustrated by numerical simulation. This is a
robust result whenever the finiteness of the niche is taken into account: it can be extended to different analytic dependence
of the interaction coefficients with the distance on the niche axis (i.e., different kernel interactions), different boundary
conditions, etc. We also found that there is a critical value both for the width of the species distribution σ and the number of species n below which the clusterization disappears.
相似文献
Egbert H. van NesEmail: |
82.
Tjisse van der Heide Egbert H. van Nes Marieke M. van Katwijk Marten Scheffer A. Jan Hendriks Alfons J. P. Smolders 《Ecosystems》2010,13(6):841-850
Many populations are exposed to naturally occurring or synthetic toxicants. An increasing number of studies demonstrate that
the toxicity of such compounds is not only dependent on the concentration or load, but also on the biomass or density of exposed
organisms. At high biomass, organisms may be able to alleviate adverse effects of the toxicant by actively lowering ambient
concentrations through either a joint detoxification mechanism or growth dilution. We show in a conceptual model that this
mechanism may potentially lead to alternative stable states if the toxicant is lethal at low densities of organisms, whereas
a high density is able to reduce the toxicant concentrations to sub-lethal levels. We show in an example that this effect
may be relevant in real ecosystems. In an earlier published experimental laboratory study, we demonstrated that ammonia toxicity
in eelgrass is highly dependent on the eelgrass shoot density. Here, we used the results of these experiments to construct
a model describing the complex interactions between the temperate seagrass Zostera marina and potentially lethal ammonia. Analyses of the model show that alternative stable states are indeed present over wide ranges
of key-parameter settings, suggesting that the mechanism might be important especially in sheltered, eutrophicated estuaries
where mixing of the water layer is poor. We argue that the same mechanism could cause alternative stable states in other biological
systems as well. 相似文献
83.
Otfried Kistner Brian A. Crowe Walter Wodal Astrid Kerschbaum Helga Savidis-Dacho Nicolas Sabarth Falko G. Falkner Ines Mayerhofer Wolfgang Mundt Manfred Reiter Leopold Grillberger Christa Tauer Michael Graninger Alois Sachslehner Michael Schwendinger Peter Brühl Thomas R. Kreil Hartmut J. Ehrlich P. Noel Barrett 《PloS one》2010,5(2)
The recent emergence and rapid spread of a novel swine-derived H1N1 influenza virus has resulted in the first influenza pandemic of this century. Monovalent vaccines have undergone preclinical and clinical development prior to initiation of mass immunization campaigns. We have carried out a series of immunogenicity and protection studies following active immunization of mice, which indicate that a whole virus, nonadjuvanted vaccine is immunogenic at low doses and protects against live virus challenge. The immunogenicity in this model was comparable to that of a whole virus H5N1 vaccine, which had previously been demonstrated to induce high levels of seroprotection in clinical studies. The efficacy of the H1N1 pandemic vaccine in protecting against live virus challenge was also seen to be equivalent to that of the H5N1 vaccine. The protective efficacy of the H1N1 vaccine was also confirmed using a severe combined immunodeficient (SCID) mouse model. It was demonstrated that mouse and guinea pig immune sera elicited following active H1N1 vaccination resulted in 100% protection of SCID mice following passive transfer of immune sera and lethal challenge. The immune responses to a whole virus pandemic H1N1 and a split seasonal H1N1 vaccine were also compared in this study. It was demonstrated that the whole virus vaccine induced a balanced Th-1 and Th-2 response in mice, whereas the split vaccine induced mainly a Th-2 response and only minimal levels of Th-1 responses. These data supported the initiation of clinical studies with the same low doses of whole virus vaccine that had previously been demonstrated to be immunogenic in clinical studies with a whole virus H5N1 vaccine. 相似文献
84.
Rameez Arshad Claudio Calvaruso Egbert J Boekema Claudia Büchel Roman Kouil 《Plant physiology》2021,186(4):2124
Diatoms are a large group of marine algae that are responsible for about one-quarter of global carbon fixation. Light-harvesting complexes of diatoms are formed by the fucoxanthin chlorophyll a/c proteins and their overall organization around core complexes of photosystems (PSs) I and II is unique in the plant kingdom. Using cryo-electron tomography, we have elucidated the structural organization of PSII and PSI supercomplexes and their spatial segregation in the thylakoid membrane of the model diatom species Thalassiosira pseudonana. 3D sub-volume averaging revealed that the PSII supercomplex of T. pseudonana incorporates a trimeric form of light-harvesting antenna, which differs from the tetrameric antenna observed previously in another diatom, Chaetoceros gracilis. Surprisingly, the organization of the PSI supercomplex is conserved in both diatom species. These results strongly suggest that different diatom classes have various architectures of PSII as an adaptation strategy, whilst a convergent evolution occurred concerning PSI and the overall plastid structure. The antenna organization of photosystem II in the diatom Thalassiosira pseudonana strongly differs from Chaetoceros gracilis, while the architecture of the photosystem I antenna remains the same. 相似文献
85.
Garcia Costas AM Tsukatani Y Romberger SP Oostergetel GT Boekema EJ Golbeck JH Bryant DA 《Journal of bacteriology》2011,193(23):6701-6711
Chlorosomes are sac-like, light-harvesting organelles that characteristically contain very large numbers of bacteriochlorophyll (BChl) c, d, or e molecules. These antenna structures occur in chlorophototrophs belonging to some members of the Chlorobi and Chloroflexi phyla and are also found in a recently discovered member of the phylum Acidobacteria, "Candidatus Chloracidobacterium thermophilum." "Ca. Chloracidobacterium thermophilum" is the first aerobic organism discovered to possess chlorosomes as light-harvesting antennae for phototrophic growth. Chlorosomes were isolated from "Ca. Chloracidobacterium thermophilum" and subjected to electron microscopic, spectroscopic, and biochemical analyses. The chlorosomes of "Ca. Chloracidobacterium thermophilum" had an average size of ~100 by 30 nm. Cryo-electron microscopy showed that the BChl c molecules formed folded or twisted, sheet-like structures with a lamellar spacing of ~2.3 nm. Unlike the BChls in the chlorosomes of the green sulfur bacterium Chlorobaculum tepidum, concentric cylindrical nanotubes were not observed. Chlorosomes of "Ca. Chloracidobacterium thermophilum" contained a homolog of CsmA, the BChl a-binding, baseplate protein; CsmV, a protein distantly related to CsmI, CsmJ, and CsmX of C. tepidum, which probably binds a single [2Fe-2S] cluster; and five unique polypeptides (CsmR, CsmS, CsmT, CsmU, and a type II NADH dehydrogenase homolog). Although "Ca. Chloracidobacterium thermophilum" is an aerobe, energy transfer among the BChls in these chlorosomes was very strongly quenched in the presence of oxygen (as measured by quenching of fluorescence emission). The combined analyses showed that the chlorosomes of "Ca. Chloracidobacterium thermophilum" possess a number of unique features but also share some properties with the chlorosomes found in anaerobic members of other phyla. 相似文献
86.
Glial glutamate transporters mediate a functional metabolic crosstalk between neurons and astrocytes in the mouse developing cortex 总被引:12,自引:0,他引:12
Voutsinos-Porche B Bonvento G Tanaka K Steiner P Welker E Chatton JY Magistretti PJ Pellerin L 《Neuron》2003,37(2):275-286
Neuron-glia interactions are essential for synaptic function, and glial glutamate (re)uptake plays a key role at glutamatergic synapses. In knockout mice, for either glial glutamate transporters, GLAST or GLT-1, a classical metabolic response to synaptic activation (i.e., enhancement of glucose utilization) is decreased at an early functional stage in the somatosensory barrel cortex following activation of whiskers. Investigation in vitro demonstrates that glial glutamate transport represents a critical step for triggering enhanced glucose utilization, but also lactate release from astrocytes through a mechanism involving changes in intracellular Na(+) concentration. These data suggest that a metabolic crosstalk takes place between neurons and astrocytes in the developing cortex, which would be regulated by synaptic activity and mediated by glial glutamate transporters. 相似文献
87.
88.
Consequences of state transitions on the structural and functional organization of Photosystem I in the green alga Chlamydomonas reinhardtii 总被引:1,自引:0,他引:1
Bartlomiej Drop Sathish Yadav K.N. Egbert J. Boekema Roberta Croce 《The Plant journal : for cell and molecular biology》2014,78(2):181-191
State transitions represent a photoacclimation process that regulates the light‐driven photosynthetic reactions in response to changes in light quality/quantity. It balances the excitation between photosystem I (PSI) and II (PSII) by shuttling LHCII, the main light‐harvesting complex of green algae and plants, between them. This process is particularly important in Chlamydomonas reinhardtii in which it is suggested to induce a large reorganization in the thylakoid membrane. Phosphorylation has been shown to be necessary for state transitions and the LHCII kinase has been identified. However, the consequences of state transitions on the structural organization and the functionality of the photosystems have not yet been elucidated. This situation is mainly because the purification of the supercomplexes has proved to be particularly difficult, thus preventing structural and functional studies. Here, we have purified and analysed PSI and PSII supercomplexes of C. reinhardtii in states 1 and 2, and have studied them using biochemical, spectroscopic and structural methods. It is shown that PSI in state 2 is able to bind two LHCII trimers that contain all four LHCII types, and one monomer, most likely CP29, in addition to its nine Lhcas. This structure is the largest PSI complex ever observed, having an antenna size of 340 Chls/P700. Moreover, all PSI‐bound Lhcs are efficient in transferring energy to PSI. A projection map at 20 Å resolution reveals the structural organization of the complex. Surprisingly, only LHCII type I, II and IV are phosphorylated when associated with PSI, while LHCII type III and CP29 are not, but CP29 is phosphorylated when associated with PSII in state2. 相似文献
89.
90.
Saskia Letz Christine Haag Egbert Schulze Karin Frank-Raue Friedhelm Raue Benjamin Hofner Bernhard Mayr Christof Sch?fl 《PloS one》2014,9(12)