全文获取类型
收费全文 | 1655篇 |
免费 | 124篇 |
出版年
2023年 | 4篇 |
2022年 | 15篇 |
2021年 | 24篇 |
2020年 | 31篇 |
2019年 | 22篇 |
2018年 | 28篇 |
2017年 | 28篇 |
2016年 | 51篇 |
2015年 | 48篇 |
2014年 | 62篇 |
2013年 | 81篇 |
2012年 | 143篇 |
2011年 | 127篇 |
2010年 | 71篇 |
2009年 | 97篇 |
2008年 | 88篇 |
2007年 | 116篇 |
2006年 | 105篇 |
2005年 | 109篇 |
2004年 | 91篇 |
2003年 | 86篇 |
2002年 | 68篇 |
2001年 | 26篇 |
2000年 | 8篇 |
1999年 | 17篇 |
1998年 | 23篇 |
1997年 | 20篇 |
1996年 | 11篇 |
1995年 | 23篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 4篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1968年 | 3篇 |
排序方式: 共有1779条查询结果,搜索用时 15 毫秒
111.
The COP1/SPA complex and DET1 function to suppress photomorphogenesis in dark-grown Arabidopsis seedlings. Additionally, they
inhibit flowering under non-inductive short-day conditions. The COP1/SPA complex and DET1, as part of the CDD complex, represent
distinct high-molecular-weight complexes in Arabidopsis. Here, we provide genetic evidence that these complexes co-act in
regulating plant development. We report the isolation of a spa1 enhancer mutation that represents a novel, very weak allele of det1. This det1
esp1
mutation caused no detectable mutant phenotype in the presence of wild-type SPA1, but showed strongly synergistic genetic interaction with the spa1 mutation in the control of seedling photomorphogenesis, anthocyanin accumulation, plant size as well as flowering time. On
the biochemical level, the det1
esp1
spa1 double mutant showed higher HY5 protein levels than either single mutant or the wild type. The genetic interaction of spa1 and det1 mutations was further confirmed in the spa1 det1-1 double mutant which carries a strong allele of det1. Taken together, these results show that SPA1 and DET1 act together to control photomorphogenesis throughout plant development.
Hence, this suggests that COP1/SPA complexes and the CDD complex co-act in controlling the protein stability of COP1/SPA target
proteins. 相似文献
112.
Sponges (Porifera) are filter feeders that take up microorganisms from seawater and digest them by phagocytosis. At the same
time, many sponges are known to harbor massive consortia of symbiotic microorganisms, which are phylogenetically distinct
from those in seawater, within the mesohyl matrix. In the present study, feeding experiments were performed to investigate
whether phylogenetically different bacterial isolates, hereafter termed “food bacteria,” microbial seawater consortia, and
sponge symbiont consortia are taken up and processed differently by the host sponge. Aplysina aerophoba retained high numbers of bacterial isolates and microbial seawater consortia with rates of up to 2.76 × 106 bacteria (g sponge wet weight)–1 h–1, whereas the retention of sponge symbionts was lower by nearly two orders of magnitude [5.37 × 104 bacteria (g sponge wet weight)−1 h–1]. In order to visualize the processing of a food bacterium within sponge tissues, the green fluorescent protein-labeled Vibrio strain MMW1, which had originally been isolated from A. aerophoba, was constructed. Incubation of this strain with A. aerophoba and subsequent visualization in tissue cryosections showed its presence in the choanocytes and/or endopinacocytes lining
the canals but, unlike latex beads, not in deeper regions of the mesohyl, which suggests digestion of the bacteria upon contact
with the host. Denaturing gradient gel electrophoresis (DGGE) was performed on the incubation seawater to monitor the changes
in phylogenetic composition after incubation of the sponge with either seawater or sponge symbiont consortia. However, the
DGGE experiment provided no evidence for selective processing of individual lineages by the host sponge. In conclusion, this
study extends early studies by Wilkinson et al. (Proc R Soc London B 220:519–528, 1984) that sponges, here A. aerophoba, are able to differentiate between food bacteria and their own bacterial symbionts. 相似文献
113.
Schmitt S Weisz JB Lindquist N Hentschel U 《Applied and environmental microbiology》2007,73(7):2067-2078
Many marine demosponges contain large amounts of phylogenetically complex yet highly sponge-specific microbial consortia within the mesohyl matrix, but little is known about how these microorganisms are acquired by their hosts. Settlement experiments were performed with the viviparous Caribbean demosponge Ircinia felix to investigate the role of larvae in the vertical transmission of the sponge-associated microbial community. Inspections by electron microscopy revealed large amounts of morphologically diverse microorganisms in the center of I. felix larvae, while the outer rim appeared to be devoid of microorganisms. In juveniles, microorganisms were found between densely packed sponge cells. Denaturing gradient gel electrophoresis (DGGE) was performed to compare the bacterial community profiles of adults, larvae, and juvenile sponges. Adults and larvae were highly similar in DGGE band numbers and banding patterns. Larvae released by the same adult individual contained highly similar DGGE banding patterns, whereas larvae released by different adult individuals showed slightly different DGGE banding patterns. Over 200 bands were excised, sequenced, and phylogenetically analyzed. The bacterial diversity of adult I. felix and its larvae was comparably high, while juveniles showed reduced diversity. In total, 13 vertically transmitted sequence clusters, hereafter termed "IF clusters," that contained sequences from both the adult sponge and offspring (larvae and/or juveniles) were found. The IF clusters belonged to at least four different eubacterial phyla and one possibly novel eubacterial lineage. In summary, it could be shown that in I. felix, vertical transmission of microorganisms through the larvae is an important mechanism for the establishment of the sponge-microbe association. 相似文献
114.
Fieseler L Hentschel U Grozdanov L Schirmer A Wen G Platzer M Hrvatin S Butzke D Zimmermann K Piel J 《Applied and environmental microbiology》2007,73(7):2144-2155
Numerous marine sponges harbor enormous amounts of as-yet-uncultivated bacteria in their tissues. There is increasing evidence that these symbionts play an important role in the synthesis of protective metabolites, many of which are of great pharmacological interest. In this study, genes for the biosynthesis of polyketides, one of the most important classes of bioactive natural products, were systematically investigated in 20 demosponge species from different oceans. Unexpectedly, the sponge metagenomes were dominated by a ubiquitously present, evolutionarily distinct, and highly sponge-specific group of polyketide synthases (PKSs). Open reading frames resembling animal fatty acid genes were found on three corresponding DNA regions isolated from the metagenomes of Theonella swinhoei and Aplysina aerophoba. Their architecture suggests that methyl-branched fatty acids are the metabolic product. According to a phylogenetic analysis of housekeeping genes, at least one of the PKSs belongs to a bacterium of the Deinococcus-Thermus phylum. The results provide new insights into the chemistry of sponge symbionts and allow inference of a detailed phylogeny of the diverse functional PKS types present in sponge metagenomes. Based on these qualitative and quantitative data, we propose a significantly simplified strategy for the targeted isolation of biomedically relevant PKS genes from complex sponge-symbiont associations. 相似文献
115.
116.
117.
On the mechanism of cerebral accumulation of cholestanol in patients with cerebrotendinous xanthomatosis 总被引:1,自引:0,他引:1
Panzenboeck U Andersson U Hansson M Sattler W Meaney S Björkhem I 《Journal of lipid research》2007,48(5):1167-1174
The most serious consequence of sterol 27-hydroxylase deficiency in humans [cerebrotendinous xanthomatosis (CTX)] is the development of cholestanol-containing brain xanthomas. The cholestanol in the brain may be derived from the circulation or from 7alpha-hydroxylated intermediates in bile acid synthesis, present at 50- to 250-fold increased levels in plasma. Here, we demonstrate a transfer of 7alpha-hydroxy-4-cholesten-3-one across cultured porcine brain endothelial cells (a model for the blood-brain barrier) that is approximately 100-fold more efficient than the transfer of cholestanol. Furthermore, there was an efficient conversion of 7alpha-hydroxy-4-cholesten-3-one to cholestanol in cultured neuronal and glial cells as well as in monocyte-derived macrophages of human origin. It is concluded that the continuous intracellular production of cholestanol from a bile acid precursor capable of rapidly passing biomembranes, including the blood-brain barrier, is likely to be of major importance for the accumulation of cholestanol in patients with CTX. Such a mechanism also fits well with the observation that treatment with chenodeoxycholic acid, which normalizes the level of the bile acid precursor, results in a reduction of cholestanol-containing xanthomas even in the brain. 相似文献
118.
Müller P Ewers C Bertsche U Anstett M Kallis T Breukink E Fraipont C Terrak M Nguyen-Distèche M Vollmer W 《The Journal of biological chemistry》2007,282(50):36394-36402
Bacterial cell division requires the coordinated action of cell division proteins and murein (peptidoglycan) synthases. Interactions involving the essential cell division protein FtsN and murein synthases were studied by affinity chromatography with membrane fraction. The murein synthases PBP1A, PBP1B, and PBP3 had an affinity to immobilized FtsN. FtsN and PBP3, but not PBP1A, showed an affinity to immobilized PBP1B. The direct interaction between FtsN and PBP1B was confirmed by pulldown experiments and surface plasmon resonance. The interaction was also detected by bacterial two-hybrid analysis. FtsN and PBP1B could be cross-linked in intact cells of the wild type and in cells depleted of PBP3 or FtsW. FtsN stimulated the in vitro murein synthesis activities of PBP1B. Thus, FtsN could have a role in controlling or modulating the activity of PBP1B during cell division in Escherichia coli. 相似文献
119.
Schmelting B Zimmermann E Berke O Bruford MW Radespiel U 《American journal of physical anthropology》2007,133(1):743-752
Male mating tactics can vary according to the potential for scramble or contest competition but also as a consequence of individual characteristics, such as body condition and previous experience. The influence of experience, i.e., residency, on male recapture rates and reproductive success was studied in a population of free-living grey mouse lemurs. Long-term capture data from 320 individuals revealed that both sexes had very low recapture probabilities within their first year in the study population, but recapture rates declined less sharply during the following years. Capture results and telemetric analyses on 12 focal males revealed that resident males had larger body mass and larger home ranges than new males. Home range size correlated with the number of accessible females, indicating that resident males had higher probabilities to meet mates than new males. The reproductive success of 132 candidate fathers, representing both resident and new males, was determined by means of molecular genotyping. Paternity determination was successful in 38 cases (success rate: 19%). Sixteen resident males and seventeen new males sired offspring. However, in relation to the number of candidate fathers being present in the mating season, resident males were twice as likely to reproduce successfully as new males. These findings suggest experience-dependent reproductive tactics that most likely correspond to a differential spatial knowledge of resources, mates and potential threats. The results generally agree with the predictions made for a scramble competition regime and demonstrate substantial behavioral plasticity in a nocturnal primate species with a dispersed multi-male/multi-female mating system. 相似文献
120.
Müller WE Eckert C Kropf K Wang X Schlossmacher U Seckert C Wolf SE Tremel W Schröder HC 《Cell and tissue research》2007,329(2):363-378
The siliceous sponge Monorhaphis chuni (Hexactinellida) synthesizes the largest biosilica structures on earth (3 m). Scanning electron microscopy has shown that
these spicules are regularly composed of concentrically arranged lamellae (width: 3–10 μm). Between 400 and 600 lamellae have
been counted in one giant basal spicule. An axial canal (diameter: ~2 μm) is located in the center of the spicules; it harbors
the axial filament and is surrounded by an axial cylinder (100–150 μm) of electron-dense homogeneous silica. During dissolution
of the spicules with hydrofluoric acid, the axial filament is first released followed by the release of a proteinaceous tubule.
Two major proteins (150 kDa and 35 kDa) have been visualized, together with a 24-kDa protein that cross-reacts with antibodies
against silicatein. The spicules are surrounded by a collagen net, and the existence of a hexactinellidan collagen gene has
been demonstrated by cloning it from Aphrocallistes vastus. During the axial growth of the spicules, silicatein or the silicatein-related protein is proposed to become associated with
the surface of the spicules and to be finally internalized through the apical opening to associate with the axial filament.
Based on the data gathered here, we suggest that, in the Hexactinellida, the growth of the spicules is mediated by silicatein
or by a silicatein-related protein, with the orientation of biosilica deposition being controlled by lectin and collagen.
Carsten Eckert was previously with the Museum für Naturkunde, Invalidenstrasse 43, 10115 Berlin, Germany.
The collagen sequence from Aphrocallistes vastus reported here, viz., [COL_APHRO] APHVACOL (accession number AM411124), has been deposited in the EMBL/GenBank data base.
This work was supported by grants from the European Commission, the Deutsche Forschungsgemeinschaft, the Bundesministerium
für Bildung und Forschung Germany (project: Center of Excellence BIOTECmarin), the National Natural Science Foundation of China (grant no. 50402023), and the International Human Frontier Science
Program. 相似文献