全文获取类型
收费全文 | 232篇 |
免费 | 19篇 |
专业分类
251篇 |
出版年
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 13篇 |
2012年 | 14篇 |
2011年 | 21篇 |
2010年 | 15篇 |
2009年 | 5篇 |
2008年 | 13篇 |
2007年 | 10篇 |
2006年 | 13篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 4篇 |
1971年 | 1篇 |
1969年 | 4篇 |
1968年 | 7篇 |
1966年 | 2篇 |
1963年 | 2篇 |
1962年 | 1篇 |
1961年 | 1篇 |
1902年 | 2篇 |
排序方式: 共有251条查询结果,搜索用时 10 毫秒
71.
Ole Munk 《Acta zoologica》1999,80(4):265-284
The article deals with the structure and presumed functions of the escal photophore found in the bulbous tip of the cephalic fin ray or illicium, situated on the upper part of the head in metamorphosed females in most species of deep-sea anglerfishes (ceratioids). The escal photophore consists of the light gland proper and certain accessory structures. An accessory structure common to all species is a lightproof cup enclosing the light gland and provided with a distal opening, while the escae in a number of ceratioids in addition posses reflecting structures, tubular modifications of which form light guides in some species. The light gland proper is a roughly oval or spherical body, typically consisting of radiating branched glandular tubules arranged around a central escal cavity which communicates with the exterior via the vestibule, a usually slit-like epithelium-lined space lying above the distal part of the light gland. All lumina within the light gland contain bioluminescent symbiotic bacteria. The esca is generally thought to function as a lure, prey being attracted by the light emitted from the photophore and movements of the illicium. A possible additional function may be the ejection of a luminous material to confuse predators. 相似文献
72.
Summary . We study the issue of identifiability of mixture models in the context of capture–recapture abundance estimation for closed populations. Such models are used to take account of individual heterogeneity in capture probabilities, but their validity was recently questioned by Link (2003, Biometrics 59, 1123–1130) on the basis of their nonidentifiability. We give a general criterion for identifiability of the mixing distribution, and apply it to establish identifiability within families of mixing distributions that are commonly used in this context, including finite and beta mixtures. Our analysis covers binomial and geometrically distributed outcomes. In an example we highlight the difference between the identifiability issue considered here and that in classical binomial mixture models. 相似文献
73.
Adults of the human parasitic trematode Schistosoma mansoni, which causes
hepatosplenic/intestinal complications in humans, synthesize
glycoconjugates containing the Lewis x (Lex) Galbeta1-->4(Fucalpha1--
>3)GlcNAcbeta1-->R, but not sialyl Lewis x (sLex), antigen. We now
report on our analyses of Lexand sLexexpression in S.haematobium and
S.japonicum, which are two other major species of human schistosomes that
cause disease, and the possible autoimmunity to these antigens in infected
individuals. Antigen expression was evaluated by both ELISA and Western
blot analyses of detergent extracts of parasites using monoclonal
antibodies. Several high molecular weight glycoproteins in both S.
haematobium and S. japonicum contain the Lexantigen, but no sialyl
Lexantigen was detected. In addition, sera from humans and rodents infected
with S.haematobium and S.japonicum contain antibodies reactive with Lex.
These results led us to investigate whether Lexantigens are expressed in
other helminths, including the parasitic trematode Fasciola hepatica , the
parasitic nematode Dirofilaria immitis (dog heartworm), the ruminant
nematode Haemonchus contortus , and the free-living nematode Caenorhabditis
elegans . Neither Lexnor sialyl-Lexis detectable in these other helminths.
Furthermore, none of the helminths, including schistosomes, express Lea,
Leb, Ley, or the H- type 1 antigen. However, several glycoproteins from all
helminths analyzed are bound by Lotus tetragonolobus agglutinin , which
binds Fucalpha1-->3GlcNAc, and Wisteria floribunda agglutinin, which
binds GalNAcbeta1-->4GlcNAc (lacdiNAc or LDN). Thus, schistosomes may be
unique among helminths in expressing the Lexantigen, whereas many different
helminths may express alpha1,3-fucosylated glycans and the LDN motif.
相似文献
74.
H Kirchner G Darai H M Hirt K Keyssner K Munk 《Journal of immunology (Baltimore, Md. : 1950)》1978,120(2):641-645
Spleen cells of B6 mice not previously immunized were induced to DNA synthesis by supernatants from HSV-infected tissue culture. The stimulatory principle could be passed through a 45-micrometer filter and sedimented at 100,000 x G. It was abolished by UV light, heating at 56 degrees C, and by an anti-HSV serum. The possibility that the observed stimulation was caused by LPS was therefore excluded, and there was a-so no indication of mycoplasma contamination. Partial purification of spleen cells from macrophages resulted in an increased stimulation by HSV. From experiments with nylon columns, anti-theta antibody, and nude mice it was concluded that HSV acted as a B cell mitogen. Strains of both HSV types 1 and 2 were stimulatory for B6 spleen cells. Of nine freshly isolated HSV strains with identical passage history (twice in HEF) four were strongly stimulatory, three showed a moderate stimulation, and two did not stimulate. Spleen cells from A/J and DBA/2 mice were stimulated to the same extent by HSV (WAL) as spleen cells from B6 mice. No viral replication was demonstrable in B6 spleen cell cultures stimulated for DNA synthesis by HSV. Thus our study demonstrates induction of cellular DNA synthesis in B lymphocytes by HSV which is abolished by inactivation of the virus. 相似文献
75.
Darai G. Flügel R. M. Braun R. Berger U. Matz B. Munk K. 《In vitro cellular & developmental biology. Plant》1978,14(6):536-542
Summary Rat and tupaia 41° C temperature variant cell clones were derived from parental embryonic cells, cloned and established in
tissue cultures. Both variant cell clones grew permanently at 41° C. The morphology of these cell clones was altered in comparison
to the original fibroblast cell clones. The cell biological characterization of the rat and tupaia 41° C temperature variant
cell clones showed that both cell clones were stable. After abolishing the selection pressure (incubation at 41° C) for more
than 10 further cell passages by incubation at 37°C and then raising the temperature again to 41° C, neither of the cell clones
lost their newly acquired property of prowing at 41° C. This fact demonstrates that the newly acquired property is certain
to be genetically manifest in both cell clones. The modal number of chromosomes of the rat 41° C temperature variant cell
clone was increased, and the case of the tupaia variant cell clone, bimodality was observed. The plating efficiency of both
cell clones did not rise significantly in comparison to the parental cells. Neither of the 41° C temperature variant cell
clones grew in semi-solid medium.
This work was partially supported by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 136. 相似文献
76.
The photophores of the presumably mesopelagic deep-sea teleost Thysanactis dentex are described. The entire chin barbel and the isolated first pectoral fin ray and its filaments contain aggregations of photocytes of the same type as those present in the body-photophores and the limbus-photophores of the eyeball. The chin barbel and the first pectoral fin ray are consequently thought to be luminous. 相似文献
77.
78.
Stephen P. Yanoviak Yonatan Munk Mike Kaspari Robert Dudley 《Proceedings. Biological sciences / The Royal Society》2010,277(1691):2199-2204
In contrast to the patagial membranes of gliding vertebrates, the aerodynamic surfaces used by falling wingless ants to direct their aerial descent are unknown. We conducted ablation experiments to assess the relative contributions of the hindlegs, midlegs and gaster to gliding success in workers of the Neotropical arboreal ant Cephalotes atratus (Hymenoptera: Formicidae). Removal of hindlegs significantly reduced the success rate of directed aerial descent as well as the glide index for successful flights. Removal of the gaster alone did not significantly alter performance relative to controls. Equilibrium glide angles during successful targeting to vertical columns were statistically equivalent between control ants and ants with either the gaster or the hindlegs removed. High-speed video recordings suggested possible use of bilaterally asymmetric motions of the hindlegs to effect body rotations about the vertical axis during targeting manoeuvre. Overall, the control of gliding flight was remarkably robust to dramatic anatomical perturbations, suggesting effective control mechanisms in the face of adverse initial conditions (e.g. falling upside down), variable targeting decisions and turbulent wind gusts during flight. 相似文献
79.
Maxim VC Greenberg Israel Ausin Simon WL Chan Shawn J Cokus Josh T Cuperus Suhua Feng Julie A Law Carolyn Chu Matteo Pellegrini James C Carrington Steven E Jacobsen 《Epigenetics》2011,6(3):344-354
De novo DNA methylation in Arabidopsis thaliana is catalyzed by the methyltransferase DRM2, a homolog of the mammalian de novo methyltransferase DNMT3. DRM2 is targeted to DNA by small interfering RNAs (siRNAs) in a process known as RNA-directed DNA Methylation (RdDM). While several components of the RdDM pathway are known, a functional understanding of the underlying mechanism is far from complete. We employed both forward and reverse genetic approaches to identify factors involved in de novo methylation. We utilized the FWA transgene, which is methylated and silenced when transformed into wild-type plants, but unmethylated and expressed when transformed into de novo methylation mutants. Expression of FWA is marked by a late-flowering phenotype, which is easily scored in mutant versus wild-type plants. By reverse genetics we discovered the requirement for known RdDM effectors AGO6 and NRPE5a for efficient de novo methylation. A forward genetic approach uncovered alleles of several components of the RdDM pathway, including alleles of clsy1, ktf1 and nrpd/e2, which have not been previously shown to be required for the initial establishment of DNA methylation. Mutations were mapped and genes cloned by both traditional and whole genome sequencing approaches. The methodologies and the mutant alleles discovered will be instrumental in further studies of de novo DNA methylation.Key words: DNA methylation, Arabidopsis, de novo, genetic screen, whole-genome sequencing 相似文献
80.