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排序方式: 共有283条查询结果,搜索用时 31 毫秒
101.
Suppression of IgE responses by passive antigen inhalation: dissociation of local (mucosal) and systemic immunity 总被引:1,自引:0,他引:1
Animals from high- and low-IgE-responder rat strains were preexposed to antigen-containing aerosols of different droplet sizes, prior to parenteral antigenic challenge. Depending upon the type of aerosol employed, systemic immunological tolerance developed in high-IgE-responder animals in the IgE antibody class either with or without concomitant production of salivary IgA, indicating that the two antibody isotypes were under independent control, and further that IgA-mediated immune exclusion was not central to the development of tolerance in the IgE class. Low-IgE-responder rats exhibited biphasic salivary IgA responses during exposure, which could not be recalled by subsequent parenteral challenge, suggesting that secretory immunity in the respiratory tract may also be down regulated by repeated exposure to airborne antigens. 相似文献
102.
103.
Gregory L. Britten Michael Dowd Cóilín Minto Francesco Ferretti Ferdinando Boero Heike K. Lotze 《Ecology letters》2014,17(12):1518-1525
Fisheries exploitation has caused widespread declines in marine predators. Theory predicts that predator depletion will destabilise lower trophic levels, making natural communities more vulnerable to environmental perturbations. However, empirical evidence has been limited. Using a community matrix model, we empirically assessed trends in the stability of a multispecies coastal fish community over the course of predator depletion. Three indices of community stability (resistance, resilience and reactivity) revealed significantly decreasing stability concurrent with declining predator abundance. The trophically downgraded community exhibited weaker top‐down control, leading to predator‐release processes in lower trophic levels and increased susceptibility to perturbation. At the community level, our results suggest that high predator abundance acts as a stabilising force to the naturally stochastic and highly autocorrelated dynamics in low trophic species. These findings have important implications for the conservation and management of predators in marine ecosystems and provide empirical support for the theory of predatory control. 相似文献
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105.
B R Hough-Evans B J Wold S G Ernst R J Britten E H Davidson 《Developmental biology》1977,60(1):258-277
106.
A. Mander C. Gouttefangeas C. Ottensmeier M. J. P. Welters L. Low S. H. van der Burg C. M. Britten 《Cancer immunology, immunotherapy : CII》2010,59(4):619-627
The Cancer Immunotherapy Immunoguiding Program has conducted an IFN-γ ELISPOT proficiency panel to examine the influence of
serum supplementation of test media on assay performance. Sixteen European laboratories analyzed the same PBMC samples using
different locally established protocols. Participants generated two simultaneous data sets—one using medium supplemented with
serum and one without serum. Performances of the two test conditions were compared by quantifying: (1) the number of viable
cells, (2) background spot formation induced in the medium only control and (3) the ability to detect antigen-specific T cell
responses. The study demonstrated that the number of viable cells recovered and the overall background spot production were
not significantly different between the two conditions. Furthermore, overall laboratory performance was equivalent for the
two test conditions; 11 out of 16 laboratories reported equal or greater detection rates using serum-free medium, while 5
laboratories reported decreased detections rates under serum-free conditions. These results show that good performance of
the IFN-γ ELISPOT assay can be achieved under serum-free conditions. Optimization of the protocol for serum-free conditions
should result in excellent detection rates and eliminate the requirement of serum batch and stability testing, allowing further
harmonization of the assay. 相似文献
107.
Forbidden synonymous substitutions in coding regions 总被引:2,自引:0,他引:2
In the evolution of highly conserved genes, a few "synonymous"
substitutions at third bases that would not alter the protein sequence are
forbidden or very rare, presumably as a result of functional requirements
of the gene or the messenger RNA. Another 10% or 20% of codons are
significantly less variable by synonymous substitution than are the
majority of codons. The changes that occur at the majority of third bases
are subject to codon usage restrictions. These usage restrictions control
sequence similarities between very distant genes. For example, 70% of third
bases are identical in calmodulin genes of man and trypanosome. Third-base
similarities of distant genes for conserved proteins are mathematically
predicted, on the basis of the G+C composition of third bases. These
observations indicate the need for reexamination of methods used to
calculate synonymous substitutions.
相似文献
108.
Monoclonal antibodies against chicken type V collagen: production, specificity, and use for immunocytochemical localization in embryonic cornea and other organs 总被引:23,自引:17,他引:6
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TF Linsenmayer JM Fitch TM Schmid Zak NB E Gibney RD Sanderson R Mayne 《The Journal of cell biology》1983,96(1):124-132
Two monoclonal antibodies have been produced against chick type V collagen and shown to be highly specific for separate, conformational dependent determinants within this molecule. When used for immunocytochemical tissue localization, these antibodies show that a major site for the in situ deposition of type V is within the extracellular matrices of many dense connective tissues. In these, however, it is largely in a form unavailable to the antibodies, thus requiring a specific “unmasking” treatment to obtain successful immunocytochemical staining. The specificity of these two IgG antibodies was determined by inhibition ELISA, in which only type V and no other known collagen shows inhibition. In ELISA, mixtures of the two antibodies give an additive binding reaction to the collagen, suggesting that each is against a different antigenic determinant. That both antigenic determinants are conformational dependent, being either in, or closely associated with, the collagen helix is demonstrated by the loss of antibody binding to molecules that have been thermally denatured. The temperature at which this occurs, as assayed by inhibition ELISA, is very similar to that at which the collagen helix melts, as determined by optical rotation. This gives strong additional evidence that the antibodies are directed against the collagen. The antibodies were used for indirect immunofluorescence analyses of cryostat sections of corneas and other organs from 17 to 18-day-old chick embryos. Of all tissues examined only Bowman’s membrane gave a strong staining reaction with cryostat sections of unfixed material. Staining in other areas of the cornea and in other tissues was very light or nonexistent. When, however, sections were pretreated with pepsin dissolved in dilute HAc or, surprisingly, with the dilute HAc itself dramatic new staining by the antibodies was observed in most tissues examined. The staining, which was specific for the anti-type V collagen antibodies, was largely confined to extracellular matrices of dense connective tissues. Experiments using protease inhibitors suggested that the “unmasking” did not involve proteolysis. We do not yet know the mechanism of this unmasking; however, one possibility is that the dilute acid causes swelling or conformational changes in a type-V collagen-containing supramolecular structure. Further studies should allow us to determine whether this is the case. 相似文献
109.
110.