全文获取类型
收费全文 | 489篇 |
免费 | 37篇 |
专业分类
526篇 |
出版年
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 16篇 |
2020年 | 13篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 10篇 |
2015年 | 17篇 |
2014年 | 30篇 |
2013年 | 30篇 |
2012年 | 39篇 |
2011年 | 41篇 |
2010年 | 14篇 |
2009年 | 23篇 |
2008年 | 29篇 |
2007年 | 21篇 |
2006年 | 31篇 |
2005年 | 16篇 |
2004年 | 18篇 |
2003年 | 21篇 |
2002年 | 19篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1978年 | 5篇 |
1976年 | 1篇 |
1969年 | 1篇 |
1968年 | 8篇 |
1965年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有526条查询结果,搜索用时 15 毫秒
91.
Silene latifolia is dioecious, yet rare hermaphrodites have been found, and such natural mutants can provide valuable insight into genetic
mechanisms. Here, we describe a hermaphrodite-inducing mutation that is almost certainly localized to the gynoecium-suppression
region of the Y chromosome in S. latifolia. The mutant Y chromosome was passed through the megaspore, and the presence of two X chromosomes was not necessary for seed
development in the parent. This result supports a lack of degeneration of the Y chromosome in S. latifolia, consistent with the relatively recent formation of the sex chromosomes in this species. When crossed to wild-type plants,
hermaphrodites performed poorly as females, producing low seed numbers. When hermaphrodites were pollen donors, the sex ratio
of offspring they produced through crosses was biased towards females. This suggests that hermaphroditic S. latifolia would fail to thrive and potentially explains the rarity of hermaphrodites in natural populations of S. latifolia. These results indicate that the Y chromosome in Silene latifolia remains very similar to the X, perhaps mostly differing in the primary sex determination regions. 相似文献
92.
The primary immunoglobulin (Ig) repertoire in the mouse develops during fetal life in the liver. The first Ig gene rearrangement--the joining of a DH to a JH gene segment--contributes largely to the diversity found in CDR3, as well as potentially encoding the D mu protein which is believed to function in the development of a B cell. In this report, the number of DJH joins in two mouse strains, C57BL/6 and BALB/c, were enumerated from days 12 to 16 of fetal development. It was found that the number of DJH structures increased from less than 300 per liver on day 12 to greater than 700,000 (C57BL/6) and 300,000 (BALB/c) on day 16. Each JH gene segment was used approximately equally on each day examined. When the DJH structures were examined by cloning and sequencing it was found that the DJH reading frame (RF) usage (with respect to JH) was not random--RF1 was used 70% of the time. Moreover, a single D gene segment, DFL16.1, was used in greater than 50% of all joins reinforcing the notion that the fetal repertoire is restricted in its antigen binding potential. 相似文献
93.
Molecular cloning of the cDNA encoding a murine sialic acid-specific 9-O-acetylesterase and RNA expression in cells of hematopoietic and non-hematopoietic origin. 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We describe the isolation of a cDNA encoding a murine sialic acid-specific 9-O-acetylesterase as well as its expression pattern in cells of both hematopoietic and non-hematopoietic origin. This enzyme catalyzes the removal of O-acetyl ester groups from position 9 of the parent sialic acid N-acetylneuraminic acid. The cDNA is 2105 nt in length and encodes a protein of 541 amino acids with a predicted molecular weight of 61 kDa, not including oligosaccharides linked to eight potential N-glycosylation sites. The cDNA encoding the acetylesterase displays a widespread distribution in various cell lines and tissues. Expression studies of B lineage cell lines and primary fetal liver cells revealed a developmentally regulated expression pattern in cells of hematopoietic origin. Given the importance of 9-O-acetylation of sialic acids, the cloning of the cDNA encoding a sialic acid-specific 9-O-acetylesterase will be helpful in understanding further the regulation of this post-translational modification and the biological consequences thereof. 相似文献
94.
Ig gene rearrangements on individual alleles of Abelson murine leukemia cell lines from (C57BL/6 x BALB/c) F1 fetal livers 总被引:4,自引:0,他引:4
M J Atkinson D A Michnick C J Paige G E Wu 《Journal of immunology (Baltimore, Md. : 1950)》1991,146(8):2805-2812
We have previously shown that selection of Ig H chain V region genes used by colonies obtained from splenic B cells and fetal liver pre-B cells was dependent on strain-specific factors. Moreover, by examining the V gene usage in strains congenic at the Igh locus, we also determined that the strain-specific factor was encoded by sequences lying outside of the Igh locus. We decided to examine whether there are differences in Vh gene rearrangement between alleles in an F1 strain. To do this analysis we chose to examine the relative Ig H chain V region gene usage of pre-B cell lines derived from (C57BL/6 x BALB/c)F1 fetal liver cells by Southern blot analysis. We found a high frequency of Vh-gene rearrangements (77% of the alleles had VDJ rearrangements) and these rearrangements occurred to Vh-genes throughout the Vh locus and were not confined to the D-proximal Vh-genes as has been previously observed with lines from other mouse strains. The Vh-gene usage pattern is similar on both alleles indicating that at least one of the determinants of which Vh-gene is used is trans-acting and acts similarly on each allele. Furthermore, one allele, Ighb (donated by the C57BL/6 parent), rearranged Vh-genes more frequently than the other allele, Igha (donated by the BALB/c parent) suggesting that one of the determinants of Vh-gene rearrangement may be acting in an allele-specific manner. 相似文献
95.
Several proteins of viral and cellular origins are myristoylated on an amino-terminal glycine residue during biosynthesis. The enzyme responsible for this modification, myristoyl CoA:protein N-myristoyltransferase (NMT), can be measured in cell-free systems by following the transfer of [3H]myristate from [3H]myristoyl CoA to a synthetic peptide substrate. We report here a procedure for the analysis of NMT activity using ion-exchange chromatography on CM-Sepharose to separate [3H]myristoyl peptide from radiolabeled reactants. This technique provides a convenient method for assaying multiple samples that is much more rapid and sensitive than procedures that rely on reversed-phase HPLC for the separation of reaction components. Characterization of this assay indicates that it is suitable for the kinetic analysis of NMT activity and for the rapid analysis of column fractions generated during the purification of NMT. 相似文献
96.
97.
98.
Fang Y Banner D Kelvin AA Huang SS Paige CJ Corfe SA Kane KP Bleackley RC Rowe T Leon AJ Kelvin DJ 《Journal of virology》2012,86(4):2229-2238
During the 2009 H1N1 influenza virus pandemic (pdmH1N1) outbreak, it was found that most individuals lacked antibodies against the new pdmH1N1 virus, and only the elderly showed anti-hemagglutinin (anti-HA) antibodies that were cross-reactive with the new strains. Different studies have demonstrated that prior contact with the virus can confer protection against strains with some degree of dissimilarity; however, this has not been sufficiently explored within the context of a pdmH1N1 virus infection. In this study, we have found that a first infection with the A/Brisbane/59/2007 virus strain confers heterologous protection in ferrets and mice against a subsequent pdmH1N1 (A/Mexico/4108/2009) virus infection through a cross-reactive but non-neutralizing antibody mechanism. Heterologous immunity is abrogated in B cell-deficient mice but maintained in CD8(-/-) and perforin-1(-/-) mice. We identified cross-reactive antibodies from A/Brisbane/59/2007 sera that recognize non-HA epitopes in pdmH1N1 virus. Passive serum transfer showed that cross-reactive sH1N1-induced antibodies conferred protection in naive recipient mice during pdmH1N1 virus challenge. The presence or absence of anti-HA antibodies, therefore, is not the sole indicator of the effectiveness of protective cross-reactive antibody immunity. Measurement of additional antibody repertoires targeting the non-HA antigens of influenza virus should be taken into consideration in assessing protection and immunization strategies. We propose that preexisting cross-protective non-HA antibody immunity may have had an overall protective effect during the 2009 pdmH1N1 outbreak, thereby reducing disease severity in human infections. 相似文献
99.
Lamb FS Hook JS Hilkin BM Huber JN Volk AP Moreland JG 《The Journal of biological chemistry》2012,287(15):12395-12404
NADPH oxidase 2 (Nox2)-generated reactive oxygen species (ROS) are critical for neutrophil (polymorphonuclear leukocyte (PMN)) microbicidal function. Nox2 also plays a role in intracellular signaling, but the site of oxidase assembly is unknown. It has been proposed to occur on secondary granules. We previously demonstrated that intracellular NADPH oxidase-derived ROS production is required for endotoxin priming. We hypothesized that endotoxin drives Nox2 assembly on endosomes. Endotoxin induced ROS generation within an endosomal compartment as quantified by flow cytometry (dihydrorhodamine 123 and Oxyburst Green). Inhibition of endocytosis by the dynamin-II inhibitor Dynasore blocked endocytosis of dextran, intracellular generation of ROS, and priming of PMN by endotoxin. Confocal microscopy demonstrated a ROS-containing endosomal compartment that co-labeled with gp91(phox), p40(phox), p67(phox), and Rab5, but not with the secondary granule marker CD66b. To further characterize this compartment, PMNs were fractionated by nitrogen cavitation and differential centrifugation, followed by free flow electrophoresis. Specific subfractions made superoxide in the presence of NADPH by cell-free assay (cytochrome c). Subfraction content of membrane and cytosolic subunits of Nox2 correlated with ROS production. Following priming, there was a shift in the light membrane subfractions where ROS production was highest. CD66b was not mobilized from the secondary granule compartment. These data demonstrate a novel, nonphagosomal intracellular site for Nox2 assembly. This compartment is endocytic in origin and is required for PMN priming by endotoxin. 相似文献
100.
Gao Y Ravert HT Valentine H Scheffel U Finley P Wong DF Dannals RF Horti AG 《Bioorganic & medicinal chemistry》2012,20(12):3698-3702
The radiosynthesis and in vivo evaluation of 5-(5-(6-[(11)C]methyl-3,6-diazabicyclo[3.2.0]heptan-3-yl)pyridin-2-yl)-1H-indole [(11)C]rac-(1), a potential PET tracer for α7 nicotinic acetylcholine receptors (α7-nAChR), are described. Syntheses of the nonradioactive standard rac-1 and corresponding desmethyl precursor 7 were achieved in several reaction steps. Radiomethylation of 7 with [(11)C]CH(3)I afforded [(11)C]rac-1 in an average radiochemical yield of 30 ± 5% (n=5) with high radiochemical purity and an average specific radioactivity of 444 ± 74 GBq/μmol (n=5). The total synthesis time was 30 min from end-of-bombardment. Biodistribution studies in mice showed that [(11)C]rac-1 penetrates the blood-brain barrier and specifically labels neuronal α7-nAChRs. 相似文献