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101.
Streptococcus pyogenes is an important human pathogen that selectively interacts with proteins involved in the humoral defense system, such as immunoglobulins and complement factors. In this report we show that S.pyogenes has the ability to hydrolyze the chitobiose core of the asparagine-linked glycan on immuno globulin G (IgG) when bacteria are grown in the presence of human plasma. This activity is associated with the secretion of a novel 108 kDa protein denoted EndoS. EndoS has endoglycosidase activity on purified soluble IgG as well as IgG bound to the bacterial surface. EndoS is required for the activity on IgG, as an isogenic EndoS mutant could not hydrolyze the glycan on IgG. In addition, we show that the secreted streptococcal cysteine proteinase SpeB cleaves IgG in the hinge region in a papain-like manner. This is the first example of an endoglycosidase produced by a bacterial pathogen that selectively hydrolyzes human IgG, and reveals a novel mechanism which may contribute to S.pyogenes pathogenesis. 相似文献
102.
Earliest Triassic microbialites in the South China block and other areas: controls on their growth and distribution 总被引:9,自引:0,他引:9
Steve Kershaw Yue Li Sylvie Crasquin-Soleau Qinglai Feng Xinan Mu Pierre-Yves Collin Alan Reynolds Li Guo 《Facies》2007,53(3):409-425
Earliest Triassic microbialites (ETMs) and inorganic carbonate crystal fans formed after the end-Permian mass extinction (ca.
251.4 Ma) within the basal Triassic Hindeodus parvus conodont zone. ETMs are distinguished from rarer, and more regional, subsequent Triassic microbialites. Large differences
in ETMs between northern and southern areas of the South China block suggest geographic provinces, and ETMs are most abundant
throughout the equatorial Tethys Ocean with further geographic variation. ETMs occur in shallow-marine shelves in a superanoxic
stratified ocean and form the only widespread Phanerozoic microbialites with structures similar to those of the Cambro-Ordovician,
and briefly after the latest Ordovician, Late Silurian and Late Devonian extinctions. ETMs disappeared long before the mid-Triassic
biotic recovery, but it is not clear why, if they are interpreted as disaster taxa. In general, ETM occurrence suggests that
microbially mediated calcification occurred where upwelled carbonate-rich anoxic waters mixed with warm aerated surface waters,
forming regional dysoxia, so that extreme carbonate supersaturation and dysoxic conditions were both required for their growth.
Long-term oceanic and atmospheric changes may have contributed to a trigger for ETM formation. In equatorial western Pangea,
the earliest microbialites are late Early Triassic, but it is possible that ETMs could exist in western Pangea, if well-preserved
earliest Triassic facies are discovered in future work. 相似文献
103.
Susan M. Theiss Thomas J. Lisney Shaun P. Collin Nathan S. Hart 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2007,193(1):67-79
Relatively little is known about the physical structure and ecological adaptations of elasmobranch sensory systems. In particular,
elasmobranch vision has been poorly studied compared to the other senses. Virtually nothing is known about whether elasmobranchs
possess multiple cone types, and therefore the potential for colour vision, or how the spectral tuning of their visual pigments
is adapted to their different lifestyles. In this study, we measured the spectral absorption of the rod and cone visual pigments
of the blue-spotted maskray, Dasyatis kuhlii, using microspectrophotometry. D. kuhlii possesses a rod visual pigment with a wavelength of maximum absorbance (λmax) at 497 nm and three spectrally distinct cone types with λmax values at 476, 498 and 552 nm. Measurements of the spectral transmittance of the ocular media reveal that wavelengths below
380 nm do not reach the retina, indicating that D. kuhlii is relatively insensitive to ultraviolet radiation. Topographic analysis of retinal ganglion cell distribution reveals an
area of increased neuronal density in the dorsal retina. Based on peak cell densities and using measurements of lens focal length
made using laser ray tracing and sections of frozen eyes, the estimated spatial resolving power of D. kuhlii is 4.10 cycles per degree. 相似文献
104.
Amyloid formation reactions exhibit two classes of polymorphisms: the metastable intermediates commonly observed during amyloid formation and the range of conformationally distinct mature fibrils often seen at the reaction endpoint. Although recent data suggest that spherical oligomers and protofibrils in most cases are not obligate intermediates of amyloid assembly, oligomeric states might sometimes serve as on-pathway intermediates. Mature amyloid polymorphs self-propagate as a result of the normally very high fidelity of amyloid elongation, giving rise to strain behavior and species barriers in prion phenomena. Oligomers, protofibrils and various polymorphic forms of mature amyloid fibrils seem to be distinguished by differences in atomic structure that give rise to differences in observed morphologies. 相似文献
105.
Question: Chronic stress events are defined as disturbance events that exceed the lifespan of the dominant plant species, fluctuate in intensity and lack abruptness or physical destruction of biomass. Can the effects of chronic stress events be measured on vegetation communities? Did two chronic stress events, the removal of a tide gate and a four year drought, cause a temporary or permanent shift in the vegetation communities of a tidal marsh? Location: Tidal marsh in southeastern United States. Methods: Change in species composition and dominance and community change on a landscape level salinity gradient were measured between time periods ranging from four months to seven years to construct a statistical baseline reference community at freshwater, oligohaline, and mesohaline sections of a tidal marsh. Statistical shifts in the plant community were defined as changes in the plant community that fell outside of the defined baseline reference community. Results: Plant community changes outside of the reference community occurred in 13 out of 378 community comparisons. Removal of the tide gate had a greater effect on interstitial salinity levels than the drought and was most intense in the oligohaline marsh, where between 20 to 45% of the freshwa‐ter/oligohaline community types permanently converted to oligohaline community types. However, community shifts in the freshwater and oligohaline marsh induced by the drought were temporary, lasting from 1 to 3+ years. Neither chronic stress event permanently altered the mesohaline plant communities. Conclusion: The effects of chronic stress events could be detected; an extended historical record of vegetation change (18 years) was necessary to identify community shifts outside of a reference condition of the community and to determine if those shifts were permanent or temporary. 相似文献
106.
DC homeostasis in hematopoietic stem cell transplantation 总被引:1,自引:0,他引:1
Hematopoietic stem cell transplantation is an important experimental tool and therapeutic modality. Its efficacy and toxicity are both linked to a GvH reaction that is initiated by donor T cells recognizing recipient APC, of which DC are the most potent. In most tissues recipient DC are replaced after transplantation because they turnover rapidly from BM-derived precursors. However, in a number of sites, notably the skin, recipient DC may persist and even self-renew for many months after transplantation. Understanding the homeostasis of different APC populations and how they are related to the induction of alloreactivity may help to improve the therapeutic benefit of transplantation. 相似文献
107.
Helena J Bailes Wayne L Davies Ann EO Trezise Shaun P Collin 《BMC evolutionary biology》2007,7(1):200
Background
One of the greatest challenges facing the early land vertebrates was the need to effectively interpret a terrestrial environment. Interpretation was based on ocular adaptations evolved for an aquatic environment millions of years earlier. The Australian lungfish Neoceratodus forsteri is thought to be the closest living relative to the first terrestrial vertebrate, and yet nothing is known about the visual pigments present in lungfish or the early tetrapods. 相似文献108.
Bett Nolan N. Hinch Scott G. Bass Arthur L. Braun Douglas C. Burnett Nicholas J. Casselman Matthew T. Cooke Steven J. Drenner S. Matthew Gelchu Ahmed Harrower William L. Ledoux Roxx Lotto Andrew G. Middleton Collin T. Minke-Martin Vanessa Patterson David A. Zhang Wenming Zhu David Z. 《Hydrobiologia》2022,849(2):385-405
Hydrobiologia - Many of the world’s rivers are dammed, altering the physiology, behaviour, ecology and survival of fish. Integrative research has the potential to improve our understanding of... 相似文献
109.
110.
The lipoprotein PulS is a dedicated chaperone that is required to target the secretin PulD to the outer membrane in Klebsiella or Escherichia coli, and to protect it from proteolysis. Here, we present indirect evidence that PulD protomers do not assemble into the secretin dodecamer before they reach the outer membrane, and that PulS reaches the outer membrane in a soluble heterodimer with the general lipoprotein chaperone LolA. However, we could not find any direct evidence for PulD protomer association with the PulS-LolA heterodimer. Instead, in cells producing PulD and a permanently locked PulS-LolA dimer (in which LolA carries an R43L substitution that prevents lipoprotein transfer to LolB in the outer membrane), LolAR43L was found in the inner membrane, probably still associated with PulS bound to PulD that had been incorrectly targeted because of the LolAR43L substitution. It is speculated that PulD protomers normally cross the periplasm together with PulS bound to LolA but when the latter cannot be separated (due to the mutation in lolA), the PulD protomers form dodecamers that insert into the inner membrane. 相似文献