首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   304篇
  免费   20篇
  2023年   1篇
  2022年   5篇
  2021年   10篇
  2020年   8篇
  2019年   13篇
  2018年   17篇
  2017年   5篇
  2016年   14篇
  2015年   10篇
  2014年   17篇
  2013年   24篇
  2012年   32篇
  2011年   27篇
  2010年   7篇
  2009年   10篇
  2008年   11篇
  2007年   7篇
  2006年   10篇
  2005年   6篇
  2004年   10篇
  2003年   9篇
  2002年   8篇
  2001年   7篇
  2000年   2篇
  1999年   2篇
  1998年   2篇
  1997年   1篇
  1996年   2篇
  1994年   1篇
  1993年   4篇
  1992年   4篇
  1991年   5篇
  1990年   5篇
  1989年   1篇
  1988年   4篇
  1987年   2篇
  1986年   6篇
  1985年   1篇
  1984年   4篇
  1983年   3篇
  1982年   1篇
  1981年   2篇
  1977年   1篇
  1971年   2篇
  1969年   1篇
排序方式: 共有324条查询结果,搜索用时 31 毫秒
61.
62.
Coloninae is a tiny and distinctive subfamily of the highly diverse family Leiodidae (round fungus and small carrion beetles). Although only one leiodid fossil is known from the Mesozoic, its taxonomic position and classification are doubtful. We describe the first definitive Coloninae fossil, Colon burmiticum Yamamoto sp. nov., from Upper Cretaceous amber of Myanmar. Our finding sheds light on the origin and early evolutionary history of this peculiar genus and its subfamily.  相似文献   
63.
64.
Cellular metabolic changes, especially to lipid metabolism, have recently been recognized as a hallmark of various cancer cells. However, little is known about the significance of cellular lipid metabolism in the regulation of biological activity of glioma stem cells (GSCs). In this study, we examined the expression and role of fatty acid synthase (FASN), a key lipogenic enzyme, in GSCs. In the de novo lipid synthesis assay, GSCs exhibited higher lipogenesis than differentiated non-GSCs. Western blot and immunocytochemical analyses revealed that FASN is strongly expressed in multiple lines of patient-derived GSCs (G144 and Y10), but its expression was markedly reduced upon differentiation. When GSCs were treated with 20 μM cerulenin, a pharmacological inhibitor of FASN, their proliferation and migration were significantly suppressed and de novo lipogenesis decreased. Furthermore, following cerulenin treatment, expression of the GSC markers nestin, Sox2 and fatty acid binding protein (FABP7), markers of GCSs, decreased while that of glial fibrillary acidic protein (GFAP) expression increased. Taken together, our results indicate that FASN plays a pivotal role in the maintenance of GSC stemness, and FASN-mediated de novo lipid biosynthesis is closely associated with tumor growth and invasion in glioblastoma.  相似文献   
65.
Nitric oxide (NO) synthase (EC 1.14.23) has been purified to apparent homogeneity from rat macrophages. The purification procedure involves affinity chromatography with adenosine 2',5'-diphosphate-agarose and gel filtration chromatography on a Superose 12 HR 10/30 column. The apparent molecular weight is 300,000 by gel filtration. On polyacrylamide gel electrophoresis in sodium dodecyl sulfate, the enzyme migrates as a single protein band with Mr = 150,000. The purified enzyme is colorless, and an absorption maximum is observed at 280 nm. The half-life of the enzyme activity is 6 h at pH 7.4 and 4 degrees C. The enzyme activity required the presence of NADPH, (6R)-5,6,7,8-tetrahydro-L-biopterin, and dithiothreitol. Although the cerebellar and endothelial enzyme require Ca2+ and calmodulin, these are not required by the macrophage enzyme. The macrophage nitric oxide synthase (an inducible enzyme) seems to be different from the cerebellar and endothelial enzyme (a constitutive enzyme).  相似文献   
66.
The resistance or susceptibility of Biomphalaria glabrata strains to strains of Schistosoma mansoni, the human blood fluke, are evidenced by the responses of snail hemocytes to sporocysts of the schistosome, both in vivo and in vitro. It is now reported that living sporocysts of the PR1 strain of S. mansoni agglutinate in the plasma of all tested strains of B. glabrata, in contrast to fixed sporocysts which agglutinate only in plasma from resistant snail strains. The agglutinating activity in resistant plasmas is not divalent cation dependent, and was not inhibited by the 26 carbohydrates and four amino acids tested. In addition, the observation that gelatinous deposits develop on transforming miracidia-sporocysts in B. glabrata plasmas is also reported. Both the agglutination and gel-formation phenomena may facilitate recognition of, and attacks on, sporocysts, thereby contributing to susceptibility and resistance in this host-parasite system.  相似文献   
67.
Eye tracking has been used to investigate gaze behaviours in individuals with autism spectrum disorder (ASD). However, traditional analysis has yet to find behavioural characteristics shared by both children and adults with ASD. To distinguish core ASD gaze behaviours from those that change with development, we examined temporo-spatial gaze patterns in children and adults with and without ASD while they viewed video clips. We summarized the gaze patterns of 104 participants using multidimensional scaling so that participants with similar gaze patterns would cluster together in a two-dimensional plane. Control participants clustered in the centre, reflecting a standard gaze behaviour, whereas participants with ASD were distributed around the periphery. Moreover, children and adults were separated on the plane, thereby showing a clear effect of development on gaze behaviours. Post hoc frame-by-frame analyses revealed the following findings: (i) both ASD groups shifted their gaze away from a speaker earlier than the control groups; (ii) both ASD groups showed a particular preference for letters; and (iii) typical infants preferred to watch the mouth rather than the eyes during speech, a preference that reversed with development. These results highlight the importance of taking the effect of development into account when addressing gaze behaviours characteristic of ASD.  相似文献   
68.
Two linear plasmid-like DNA elements, designated pLP01 and pLP02, have been isolated from a strain of Pleurotus ostreatus, an edible basidiomycete. pLP01 (10.0 kb) and pLP02 (9.4 kb) were found in mitochondrial preparations of the fungus and appear to have 5' ends blocked by association of a protein. Proteinase K cleavability of the 5'-terminal protein of pLP01 was higher than that of pLP02, indicating that the terminal proteins of both plasmid-like elements are distinct from one another. pLP01 and pLP02 were estimated to be present to the extent of 1-2 copies each per mitochondrial genome equivalent. The two plasmid-like elements had no homology between them and also were not homologous with the mitochondrial and nuclear genomic DNAs of the fungus.  相似文献   
69.
The photocatalytic activity of titanium dioxide is widely utilized in science and technology. In the biological field, titanium dioxide is believed to be a disinfectant because it produces reactive oxygen species (ROS). However, there are multiple types of ROS such as hydroxyl radicals, superoxide anions, singlet oxygen, and hydrogen peroxide. In this study, we attempted to characterize the various mechanisms and roles of ROS in disinfection. Surprisingly, we found that titanium dioxide protected yeast cells from ultraviolet irradiation. We characterized the ROS produced under these conditions. The production of hydroxyl radicals and superoxide anions was confirmed; however, glucose in the yeast medium scavenged hydroxyl radicals. The photocatalytic activity of titanium dioxide produced oxidative products and reductive products, as oxidation and reduction occurred simultaneously. Once hydroxyl radicals are scavenged, the photocatalytic activity of titanium dioxide produces a reductive environment for fermenting yeast cells and protects them from oxidative stress by ultraviolet irradiation.  相似文献   
70.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号