全文获取类型
收费全文 | 222篇 |
免费 | 20篇 |
出版年
2023年 | 2篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2014年 | 7篇 |
2013年 | 9篇 |
2012年 | 19篇 |
2011年 | 13篇 |
2010年 | 4篇 |
2009年 | 11篇 |
2008年 | 14篇 |
2007年 | 7篇 |
2006年 | 9篇 |
2005年 | 15篇 |
2004年 | 3篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 2篇 |
1966年 | 4篇 |
1955年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有242条查询结果,搜索用时 31 毫秒
1.
J A Hoxie D M Matthews K J Callahan D L Cassel R A Cooper 《Journal of immunology (Baltimore, Md. : 1950)》1986,137(4):1194-1201
Phorbol esters are known to alter the expression of surface antigens and receptors on a variety of mammalian cell types. On T lymphoblastoid cell lines and peripheral blood T cells, phorbol esters have been shown to selectively reduce the expression of the T4 antigen. To more fully characterize this process, we have examined the metabolic requirements for this phorbol ester effect, and have evaluated the relationship between phorbol ester-induced T4 loss and the expression of receptors for phorbol-12,13-dibutyrate (PDB) on purified peripheral blood T4 cells. We observed that the loss of T4 on peripheral blood lymphocytes (PBL) occurred at PDB concentrations at which 10 to 15% of phorbol ester binding sites were occupied. The loss of T4 was inhibited at 4 degrees C, and by azide, methylamine, and sodium fluoride, but not by inhibitors of DNA synthesis. When cells were exposed to phorbol esters for greater than 2 days, the T4 antigen was again expressed on the cell surface despite the continued presence of phorbol esters. Cells which had recovered T4 were resistant to the effects of freshly added PDB on this antigen, and this resistance correlated with a 55% reduction in phorbol ester binding sites. Studies on fixed PBL T4 cells and MOLT-4 cells by immunofluorescence microscopy demonstrated that the decreased expression of T4 from the cell surface correlated with a bright clustering of T4 within the cytoplasm, indicating that PDB had induced an internalization of this antigen. These observations demonstrate that the binding of phorbol esters to specific receptors on lymphocytes initiates metabolically dependent events which result in the internalization of the T4 antigen. These findings may be relevant to mechanisms by which T4 functions as a signal-transducing molecule in vivo. 相似文献
2.
Nitrate reductase: an improved assay method for phytoplankton 总被引:1,自引:0,他引:1
Hochman Ayala; Nissany Aliza; Wynne David; Kaplan Bina; Berman Thomas 《Journal of plankton research》1986,8(2):385-392
A new assay for measuring the activity of nitrate reductasein phytoplankton, based upon the permeability of cells treatedwith toluene to substrates and products, is described. The methodis simple and, since the reaction is carried out directly ona glass fiber filter, can be easily performed in the field oron shipboard. In comparison with previous methods, this techniquegave higher absolute amounts of NO2 formed per unit tuneand higher enzymatic activities per sample volume when testedwith axenic algal cultures and with natural phytoplankton populationsfrom Lake Kinneret, the River Jordan and the Eastern Mediterranean. 相似文献
3.
Gordon S. A. B. Stewart Sharon Lubinsky-Mink Clive G. Jackson Aliza Cassel Jonathan Kuhn 《Plasmid》1986,15(3):172-181
During the construction of the Messing pUC plasmid series, the rop(rom) gene of pBR322 which mediates the activity of RNAI was deleted. This has resulted in an elevated copy number for the pUC plasmids which makes the expression of beta-galactosidase activity constitutive in a host containing the Iqtss lac repressor. We describe the construction of a new series of vectors which retain the pUC multiple cloning site (MCS) but in which copy number control has been recovered. In addition, the lac alpha/lac promoter expression region has been inserted into a HpaI cassette. This facilitates the movement of recombinant DNA clones within the MCS. It also increases the complementation activity of the lac alpha peptide by an order of magnitude, allowing selection of recombinants by their Lac- phenotype on MacConkey agar. 相似文献
4.
Mammal Research - Foraging animals must contend with fluctuating environmental variables that affect foraging success, including conditions like wind noise, which could diminish the usefulness of... 相似文献
5.
Sympathetic Sprouting: Time Course of Changes of Noradrenergic, Cholinergic, and Serotonergic Markers in the Denervated Rat Hippocampus 总被引:1,自引:1,他引:0
R. Jackisch B. Neufang G. Hertting H. Jeltsch C. Kelche B. Will J. C. Cassel 《Journal of neurochemistry》1995,65(1):329-337
Abstract: As a first step for experiments investigating the presynaptic characteristics of sympathetic fibers grown into the denervated hippocampus, we studied the time course of changes of neurochemical markers in the rat hippocampus, subsequent to aspiration lesions of the fimbria-fornix and the overlying callosal and cortical structures. At various postsurgical delays (1, 2, 8, 24, and 40 weeks), the activity of choline acetyltransferase, the high-affinity synaptosomal uptake of choline and noradrenaline, and the concentrations of noradrenaline, serotonin, and 5-hydroxyindoleacetic acid were measured in a dorsal, an intermediate, and a ventral part of the hippocampus. Levels of all markers were significantly reduced shortly (1–2 weeks) after the lesions. However, whereas the cholinergic (choline uptake and choline acetyltransferase activity) and the serotonergic (concentrations of serotonin and 5-hydroxyindoleacetic acid) markers remained significantly reduced for up to 40 weeks, both noradrenergic markers recovered to near-normal (noradrenaline uptake) or even supranormal (noradrenaline concentration) levels, although with clear-cut differences in the time course and the regional characteristics. The noradrenaline content reached control levels already 8 weeks after lesion surgery and was about two to three times higher 40 weeks later, with the most dramatic effects in the ventral hippocampus. In contrast, high-affinity noradrenaline uptake reached control values only 24 weeks after lesion and exceeded them only in the ventral hippocampus 40 weeks after surgery. It is concluded (a) that hippocampal noradrenaline concentration is a more sensitive marker for sympathetic sprouting than high-affinity noradrenaline uptake and (b) that functional in vitro studies on hippocampal sympathetic ingrowth appear to fit optimal conditions in the ventral hippocampus at a delay of at least 40 weeks after surgery. 相似文献
6.
Chloe Robins Yue Liu Wen Fan Duc M. Duong Jacob Meigs Nadia V. Harerimana Ekaterina S. Gerasimov Eric B. Dammer David J. Cutler Thomas G. Beach Eric M. Reiman Philip L. De Jager David A. Bennett James J. Lah Aliza P. Wingo Allan I. Levey Nicholas T. Seyfried Thomas S. Wingo 《American journal of human genetics》2021,108(3):400-410
7.
Eliana Buenaventura Krzysztof Szpila Brian K. Cassel Brian M. Wiegmann Thomas Pape 《Systematic Entomology》2020,45(2):281-301
Sarcophagidae is one of the most species-rich families within the superfamily Oestroidea. This diversity is usually represented by three lineages: Miltogramminae, Paramacronychiinae and Sarcophaginae. Historically, the phylogenetic relationships among these lineages have been elusive, due to poorly supported hypotheses or small taxon sets, or both. This study provides a dramatic increase in molecular data, more balanced sampling of all three lineages from all biogeographical regions and a reassessment of morphological characters using scanning electron microscopy in the most comprehensive assessment of subfamily-level phylogeny in Sarcophagidae to date. This analysis of the largest molecular dataset ever produced for a phylogenetic analysis of a fly lineage, with 950 loci from anchored hybrid enrichment comprising 435 930 bp from 101 species, revealed Paramacronychiinae as sister to Miltogramminae, not to Sarcophaginae, as suggested by adult morphology. Maximum likelihood analysis produced a well-supported topology, with 91% of the nodes receiving strong bootstrap proportions (> 97%). In contrast to the molecular data, three out of nine morphological characters studied point to a sister-group relationship of (Sarcophaginae + Paramacronychiinae) and the remaining six characters are either silent on subfamily relationships or in need of further study. Re-examination of morphological structures provides new insights into the evolution of male genitalic traits within Sarcophagidae and highlights their convergence producing conflicting phylogenetic signal. Our phylogeny reconciles older and widely used systems of classification with tree-based thinking and sets up a classification of flesh flies that is more aligned with their evolutionary history. 相似文献
8.
9.
Michelle R. Kaufman Marina Smelyanskaya Lynn M. Van Lith Elizabeth C. Mallalieu Aliza Waxman Karin Hatzhold Arik V. Marcell Susan Kasedde Gissenge Lija Nina Hasen Gertrude Ncube Julia L. Samuelson Collen Bonnecwe Kim Seifert-Ahanda Emmanuel Njeuhmeli Aaron A. R. Tobian 《PloS one》2016,11(3)
Background
Voluntary medical male circumcision (VMMC) is a critical HIV prevention tool. Since 2007, sub-Saharan African countries with the highest prevalence of HIV have been mobilizing resources to make VMMC available. While implementers initially targeted adult men, demand has been highest for boys under age 18. It is important to understand how male adolescents can best be served by quality VMMC services.Methods and Findings
A systematic literature review was performed to synthesize the evidence on best practices in adolescent health service delivery specific to males in sub-Saharan Africa. PubMed, Scopus, and JSTOR databases were searched for literature published between January 1990 and March 2014. The review revealed a general absence of health services addressing the specific needs of male adolescents, resulting in knowledge gaps that could diminish the benefits of VMMC programming for this population. Articles focused specifically on VMMC contained little information on the adolescent subgroup. The review revealed barriers to and gaps in sexual and reproductive health and VMMC service provision to adolescents, including structural factors, imposed feelings of shame, endorsement of traditional gender roles, negative interactions with providers, violations of privacy, fear of pain associated with the VMMC procedure, and a desire for elements of traditional non-medical circumcision methods to be integrated into medical procedures. Factors linked to effective adolescent-focused services included the engagement of parents and the community, an adolescent-friendly service environment, and VMMC counseling messages sufficiently understood by young males.Conclusions
VMMC presents an opportune time for early involvement of male adolescents in HIV prevention and sexual and reproductive health programming. However, more research is needed to determine how to align VMMC services with the unique needs of this population. 相似文献10.