全文获取类型
收费全文 | 418篇 |
免费 | 59篇 |
专业分类
477篇 |
出版年
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 10篇 |
2013年 | 15篇 |
2012年 | 18篇 |
2011年 | 16篇 |
2010年 | 10篇 |
2009年 | 10篇 |
2008年 | 11篇 |
2007年 | 10篇 |
2005年 | 14篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 16篇 |
2001年 | 11篇 |
2000年 | 18篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1993年 | 8篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1983年 | 8篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1974年 | 9篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1969年 | 4篇 |
1967年 | 7篇 |
1965年 | 4篇 |
1959年 | 5篇 |
1957年 | 5篇 |
1954年 | 4篇 |
1952年 | 3篇 |
1951年 | 3篇 |
排序方式: 共有477条查询结果,搜索用时 15 毫秒
1.
2.
Patterns of immunoenhancement and suppression induced by Chlamydia trachomatis in vivo and in vitro 总被引:1,自引:0,他引:1
We investigated the cycle of immune enhancement and suppression seen in mice infected with Chlamydia trachomatis by using in vivo and in vitro model systems. BALB/c mice injected intravenously with chlamydia reveal a three- to seven-fold increase in numbers of plaque-forming cells producing antibodies against sheep red blood cells (SRBC), when immunized with SRBC 0 to 5 days after chlamydia infection. When mice are injected with SRBC 10 to 15 days after initial chlamydia infection, the specific anti-SRBC plaque-forming cell response is suppressed two- to three-fold. In vitro, low numbers (2 to 5 X 10(6) bacteria/ml) of chlamydia stimulate potent proliferative responses by B lymphocytes while high numbers (25 X 10(6) bacteria/ml) of bacteria generate strong, general T suppressor activity. This model has important implications for regulation of immune responses that arise at different times during chlamydial infections, as well as for the potential effectiveness of chlamydial vaccines. 相似文献
3.
Promotion of Stomatal Opening by Indoleacetic Acid and Ethrel in Epidermal Strips of Vicia faba L 总被引:4,自引:2,他引:2
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Indole-3-acetic acid (IAA), at concentrations of 0.01 to 1.0 millimolar, and ethephon (0.3% v/v Ethrel) promote stomatal opening when applied to epidermal peels of Vicia faba L. in light or dark. The effect of ethylene is seen by 30 minutes and maximal opening (over two times that of untreated controls) occurs after only 60 to 90 minutes in the light. Stomatal opening by IAA and Ethrel in both light and dark is prevented by 0.14 millimolar AgCl. It is suggested that the effect of added IAA, but not that of light, is linked to ethylene production. The possible role of ethylene in stomatal opening during fungal infection is discussed. The stomates of Vicia faba provide a new system to study the effects of ethylene on certain membrane-regulated processes. 相似文献
4.
As a model system for analysing interactions between chlamydiae and myeloid cells and their precursors, we have studied binding, ingestion and destruction of Chlamydia trachomatis (L2 serovar) by the human promyelocytic cell line HL-60. HL-60 cells were induced by phorbol myristate acetate (PMA) and dimethyl sulphoxide (DMSO) to differentiate along either the macrophage or the granulocyte pathway, respectively. Using an immunofluorescence assay and electron microscopy, we have shown that induced (differentiated) HL-60 cells, but not uninduced (undifferentiated) HL-60 or other cell lines treated with PMA or DMSO, exhibit increased binding, ingestion and elimination of C. trachomatis; these activities are associated with specific histochemical and antigenic markers of myeloid differentiation. These results suggest that myeloid cells acquire the ability to interact with and kill chlamydiae during cell development. 相似文献
5.
Cytotoxic and cytolytic activity of nonadecafluoro-n-decanoic acid on Acholeplasma laidlawii.
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We studied the interactions between the perfluorinated fatty acid nonadecafluoro-n-decanoic acid (NDFDA) and the cell wall-less procaryote Acholeplasma laidlawii, which were cultured in an identical medium base but with different serum supplements. When grown in mycoplasma media supplemented with PPLO serum fraction (Difco Laboratories, Detroit, Mich.), A. laidlawii was rapidly killed by low concentrations of toxicant (less than 1.0 mM). At higher concentrations (greater than 10 mM), NDFDA treatment appeared to lyse cells. A. laidlawii cells grown in horse serum-supplemented mycoplasma media were both killed and lysed at the same NDFDA concentration (greater than 10 mM). These data suggest that this perfluorinated fatty acid can be cytotoxic and cytolytic to mycoplasmas. Changes in active concentrations occurred in parallel with changes in growth medium serum supplementation, which is known to alter mycoplasma membrane composition. We propose that NDFDA interacts with the membranes of A. laidlawii cells, resulting in cell death or cell lysis or both. 相似文献
6.
7.
V B Hatcher N Fadl-Allah M A Levitt A Brown S S Margossian P B Gordon 《Journal of cellular physiology》1986,128(3):353-361
Human endothelial cells release components into the growth medium that stimulate cell-substratum adhesion. Several macromolecular components were isolated by ultracentrifugation of the endothelial cell conditioned medium. The components were heterogeneous, consisting of several sizes when examined by sedimentation velocity and gel filtration. When the extracellular components were evaluated by electron microscopy, structurally discrete particles were observed. The extracellular components and the complexes mediated cell-substratum adhesion to both human umbilical and arterial endothelial cells. The majority of the extracellular components that promote endothelial cell adhesion were pelleted by ultracentrifugation. Although the complexes contained fibronectin, antibodies to fibronectin did not inhibit cell adhesion to the complexes. Significant inhibition of endothelial cell adhesion was observed in the presence of heparin and heparan sulfate. The supernatant fraction following ultracentrifugation of the growth medium contained a component that suppressed endothelial cell adhesion to culture dishes coated with fibronectin, type I collagen, and endothelial cell complexes. SDS-polyacrylamide gel electrophoresis indicated that the complexes contained several components, and the majority of the large-molecular-weight components were pelleted by ultracentrifugation. The conditioned medium from human endothelial cells contains specific complexes that promote cell-substratum adhesion and components that suppress cell-substratum adhesion. 相似文献
8.
Both species of chlamydia and two biovars of Chlamydia trachomatis stimulate mouse B lymphocytes 总被引:4,自引:0,他引:4
We have investigated the ability of both species of chlamydiae (C. trachomatis and C. psittaci), two major biovars of C. trachomatis (lymphogranuloma venereum and trachoma), and the two developmental forms of chlamydia (reticulate and elementary bodies) to stimulate murine spleen lymphocytes. All of these forms of the bacteria induce potent proliferation and differentiation to plaque-forming cells by B lymphocytes in vitro. Chlamydiae induce a broad antibody response, suggesting that stimulation is polyclonal in nature. Although all chlamydiae possess a lipopolysaccharide (LPS) genus-specific molecule similar to LPS found on Re mutant enterobacteria, polyclonal B cell stimulation is likely caused by molecules other than LPS, since i) polymyxin B failed to inhibit chlamydia-induced immunostimulation and ii) C3H/HeJ mice (LPS nonresponders) produced normal numbers of PFC after culture with chlamydia (but not LPS). Thus, a cross-species moiety that is not LPS is responsible for polyclonal stimulation by chlamydia. Because these bacteria can exist in latent forms in an animal, and all forms are immunostimulatory, the question of whether these bacteria can alter immune responses if released during other infections or immunizations has been raised. 相似文献
9.
Strong electrolyte continuum theory solution for equilibrium profiles, diffusion limitation, and conductance in charged ion channels. 总被引:4,自引:3,他引:1
下载免费PDF全文
![点击此处可从《Biophysical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
D G Levitt 《Biophysical journal》1985,48(1):19-31
The solution for the ion flux through a membrane channel that incorporates the electrolyte nature of the aqueous solution is a difficult theoretical problem that, until now, has not been properly formulated. The difficulty arises from the complicated electrostatic problem presented by a high dielectric aqueous channel piercing a low dielectric lipid membrane. The problem is greatly simplified by assuming that the ratio of the dielectric constant of the water to that of the lipid is infinite. It is shown that this is a good approximation for most channels of biological interest. This assumption allows one to derive simple analytical expressions for the Born image potential and the potential from a fixed charge in the channel, and it leads to a differential equation for the potential from the background electrolyte. This leads to a rigorous solution for the ion flux or the equilibrium potential based on a combination of the Nernst-Planck equation and strong electrolyte theory (i.e., Gouy-Chapman or Debye-Huckel). This approach is illustrated by solving the system of equations for the specific case of a large channel containing fixed negative charges. The following characteristics of this channels are discussed: anion and mono- and divalent cation conductance, saturation of current with increasing concentration, current-voltage relationship, influence of location and valence of fixed charge, and interaction between ions. The qualitative behavior of this channel is similar to that of the acetylcholine receptor channel. 相似文献
10.
Hardies SC; Martin SL; Voliva CF; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1986,3(2):109-125