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   1849篇
  免费   127篇
  2023年   5篇
  2022年   26篇
  2021年   37篇
  2020年   20篇
  2019年   43篇
  2018年   39篇
  2017年   30篇
  2016年   60篇
  2015年   94篇
  2014年   96篇
  2013年   122篇
  2012年   139篇
  2011年   146篇
  2010年   75篇
  2009年   87篇
  2008年   107篇
  2007年   117篇
  2006年   84篇
  2005年   74篇
  2004年   91篇
  2003年   96篇
  2002年   83篇
  2001年   26篇
  2000年   19篇
  1999年   21篇
  1998年   24篇
  1997年   16篇
  1996年   12篇
  1995年   10篇
  1994年   12篇
  1993年   10篇
  1992年   15篇
  1991年   15篇
  1990年   8篇
  1989年   8篇
  1988年   6篇
  1987年   9篇
  1986年   7篇
  1985年   7篇
  1984年   5篇
  1983年   6篇
  1982年   6篇
  1980年   6篇
  1977年   4篇
  1976年   4篇
  1974年   8篇
  1971年   4篇
  1970年   5篇
  1968年   4篇
  1966年   8篇
排序方式: 共有1976条查询结果,搜索用时 187 毫秒
61.
Cell-based therapies using adipose-derived mesenchymal stromal cells (ADMSCs) have shown promising results for the treatment of osteoarthritis (OA). In fact, ADMSCs are now indicated as one of the most powerful cell sources through their immunomodulatory and anti-inflammatory activities. Recently, an innovative one-step closed device was developed to obtain microfragmented adipose tissue (MF) to avoid the need for good manufacturing practices for ADMSCs expansion while maintaining their regenerative potential. The aim of this study was to assess the mechanisms of action of MF and ADMSCs from MF (MF-ADMSCs) on an inflammatory cell model of OA synoviocytes. We found that MF produced low levels of inflammatory factors such as interleukin 6 (IL-6), CC-chemokine ligand 5/receptor-activated normal T-cell expressed and secreted (CCL5/RANTES), CC-chemokine ligand 2/monocyte chemoattractant protein-1 (CCL2/MCP-1), and CC-chemokine ligand 3/macrophage inflammatory protein-1α (CCL3/MIP-1α), and a higher level only of CXC-chemokine ligand 8/interleukin 8 compared with MF-ADMSCs. Matrix metalloproteinase 9 (MMP-9) degradative factor but released a lower level of its inhibitor tissue inhibitor of the metalloproteinase (TIMP-1). MF in coculture with synoviocytes significantly induced both the metabolic activity and the release of IL-6. In contrast, MF, not MF-ADMSCs, partially decreased CCL5/RANTES. Moreover, MF reduced the release of both macrophage-specific chemokines (CCL2/MCP-1 and CCL3/MIP-1α) and degradative marker MMP-9. Interestingly, MF increased TIMP-1 (the MMP-9 inhibitor) and down-modulated toll-like receptor (TLR4) receptor and key molecules of NFκB pathways. These data evidenced different effects of MF versus MF-ADMSCs on inflamed synoviocytes. MF reduced typical macrophages markers and its potentiality by switching off macrophages activity was strictly dependent on TLR4 and NFκB signaling.  相似文献   
62.
The plasma membrane-associated sialidase NEU3 is known to play important roles in different physiological and pathophysiological processes such as proliferation, cellular differentiation and tumorigenesis. Up-regulation of NEU3 has been associated to several tumors and recently it was demonstrated that its down-modulation in glioblastoma cells promotes cell invasiveness. To date, no information concerning the possible role played by NEU3 in relation to tumor radioresistance is available. Here we show that overexpression of NEU3 in glioblastoma U87MG cells activates PI3K/Akt signaling pathway resulting in an increased radioresistance capacity and in an improved efficiency of double strand DNA-repair mechanisms after irradiation. Our results demonstrate for the first time that NEU3 contributes to the radioresistance features of U87MG cells, bringing to evidence a novel rand peculiar role of the enzyme in cancer biology.  相似文献   
63.
We focus on a case study along an English canal comparing environmental DNA (eDNA) metabarcoding with two types of electrofishing techniques (wade-and-reach and boom-boat). In addition to corroborating data obtained by electrofishing, eDNA provided a wider snapshot of fish assemblages. Given the semi-lotic nature of canals, we encourage the use of eDNA as a fast and cost-effective tool to detect and monitor whole fish communities.  相似文献   
64.
Brain metastases, the most common metastases in adults, will develop in up to 40% of cancer patients, accounting for more than one-half of all intracranial tumors. They are most associated with breast and lung cancer, melanoma and, less frequently, colorectal and kidney carcinoma.Magnetic resonance imaging (MRI) is the gold standard for diagnosis. For the treatment plan, computed tomography (CT ) images are co-registered and fused with a gadolinium-enhanced T1-weighted MRI where tumor volume and organs at risk are contoured. Alternatively, plain and contrast-enhanced CT scans are co-registered. Single-fraction stereotactic radiotherapy (SRT ) is used to treat patients with good performance status and up to 4 lesions with a diameter of 30 mm or less that are distant from crucial brain function areas. Fractionated SRT (2–5 fractions) is used for larger lesions, in eloquent areas or in proximity to crucial or surgically inaccessible areas and to reduce treatment-related neurotoxicity. The single-fraction SRT dose, which depends on tumor diameter, impacts local control. Fractionated SRT may encompass different schedules. No randomized trial data compared the safety and efficacy of single and multiple fractions. Both single-fraction and fractionated SRT provide satisfactory local control rates, tolerance, a low risk of transient acute adverse events and of radiation necrosis the incidence of which correlated with the irradiated brain volume.  相似文献   
65.
We have recently described in cord blood T cells (CBTC) a novel pathway linking CD38 and CD73, two signal transducers with ecto-enzyme activity. The aim of this study was 2-fold: first, to characterize the mechanisms by which CD38 regulates CD73 expression; and second, to determine whether surface-induced CD73 modulates CBTC responses. A marked increase in CD73 expression was observed in CD38+ cells after incubation with the appropriate CD38 mAbs. The induction of CD73 was blocked by wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase (PI3-K). CD38 stimulation induced tyrosine phosphorylation of the p85 regulatory subunit of PI3-K and its association with other tyrosine-phosphorylated proteins. Surface-induced CD73 was as efficient in delivering activatory signals as the CD73 constitutively expressed on adult T cells. Highly CBTC, totally unresponsive to mitogenic concentrations of plastic-immobilized CD3 mAb, proliferated vigorously when exposed to the combination of plastic-immobilized CD3 and CD73 mAbs. The reactivity to allogeneic irradiated PBMC was also significantly enhanced by CD38 stimulation and was dependent on CD73 expression. Thus, CD38 stimulation lowers the activation threshold of CBTC by the CD3/TCR complex and enhances their reactivity to allogeneic cells via activation of the PI3-kinase pathway and CD73 expression.  相似文献   
66.
Both enantiomers of "para-hydroxymexiletine" (PHM), one of the main metabolites of mexiletine, were synthesized and fully characterized. Properties of (R)- and (S)-PHM, in terms of blocking potency and stereoselectivity on frog skeletal muscle Na(+) channels, were evaluated. The presence of a hydroxy group on the aryloxy moiety in the 4-position, as in PHM, reduced potency with respect to mexiletine in reducing I(Na max). However, PHM showed clear use-dependent behavior similar to that of mexiletine and, in contrast with what is observed with the parent compound, maintained its stereoselectivity during the use-dependent block. Chirality 16:72-78, 2004.  相似文献   
67.
The class III pistil-specific extensin-like proteins (PELPIII) of Nicotiana tabacum accumulate in the intercellular matrix (IM) of the style transmitting tissue (TT). After pollination, the 110–140 kDa PELPIII is translocated from the IM into the pollen tube walls. PELPIII-like sequences have been found in several solanaceous species. These sequences are expressed in mature non-pollinated styles at both RNA and protein level. Of the genus Nicotiana, the species N. alata, N. x sanderae and N. sylvestris (section Alatae), and N. tomentosiformis and N. otophora (section Tomentosae) showed an expression level of PELPIII homologues similar to that in mature styles of N. tabacum. PELPIII genes were absent in the most ancient species studied, namely N. trigonophylla (section Trigonophyllae). To study the species dependence of the translocation of PELPIII into the pollen tube wall in tobacco, interspecific pollinations on N. tabacum pistils were carried out with pollen from the incongruous species N. rustica, N. trigonophylla and Petunia hybrida, where PELPIII homologues are absent in the style. Immunocytological tests showed that the N. tabacum PELPIII is translocated into the pollen tube walls of all three species. Thus, the pollen tube walls of these species do not form a barrier for IM compounds such as the 110–140 kDa PELPIII and the absence of any possible effect of PELPIII on pollen tube growth cannot be due to failure of PELPIII transport through the wall. The importance of these findings is discussed with respect to the evolutionary origin of PELPIII, the pollen pistil interaction, the function of style TT-specific proteins and the physical properties of pollen tube walls.  相似文献   
68.
The present study was carried out in order to investigate if there was really a failure of PCR in identifying parasitologically positive tsetse flies in the field. Tsetse flies (Glossina palpalis gambiensis and Glossina morsitans morsitans) were therefore experimentally infected with two different species of Trypanosoma (Trypanosoma brucei gambiense or Trypanosoma congolense). A total of 152 tsetse flies were dissected, and organs of each fly (midgut, proboscis or salivary glands) were examined. The positive organs were then analysed using PCR. Results showed that, regardless of the trypanosome species, PCR failed to amplify 40% of the parasitologically positive midguts. This failure, which does not occur with diluted samples, is likely to be caused by an inhibition of the amplification reaction. This finding has important implications for the detection and the identification of trypanosome species in wild tsetse flies.  相似文献   
69.
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