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   702篇
  免费   90篇
  2021年   14篇
  2020年   16篇
  2019年   5篇
  2018年   13篇
  2017年   8篇
  2016年   18篇
  2015年   32篇
  2014年   32篇
  2013年   41篇
  2012年   54篇
  2011年   33篇
  2010年   31篇
  2009年   18篇
  2008年   35篇
  2007年   25篇
  2006年   24篇
  2005年   27篇
  2004年   30篇
  2003年   30篇
  2002年   28篇
  2001年   17篇
  2000年   16篇
  1999年   17篇
  1998年   7篇
  1997年   5篇
  1996年   11篇
  1995年   7篇
  1994年   5篇
  1993年   7篇
  1992年   10篇
  1991年   9篇
  1990年   5篇
  1989年   6篇
  1987年   11篇
  1986年   11篇
  1984年   9篇
  1983年   6篇
  1982年   11篇
  1981年   7篇
  1979年   7篇
  1978年   9篇
  1977年   7篇
  1976年   7篇
  1975年   5篇
  1974年   9篇
  1973年   6篇
  1972年   7篇
  1971年   5篇
  1969年   7篇
  1937年   4篇
排序方式: 共有792条查询结果,搜索用时 15 毫秒
21.
We have previously shown that the insulin-like growth factor-2 (IGF-2) gene is partially coexpressed with the IGF-1 and -2 receptor genes in proliferative cytotrophoblasts of the human extraembryonic tissue. Here we show that high levels of IGF-2 gene expression are not restricted to the embryonic tissue but can also be found in the decidua compacta. The IGF-2 gene is thus expressed at high levels in the mesenchymal stroma of the decidua to establish potentially short-range communication with primarily IGF-1 receptor-positive mesenchymal stroma cells. Conversely, the glandular and surface epithelia coexpress the IGF-1 receptor and IGF-1 genes, while the IGF-2 gene is not detected above background levels. The potential control mechanisms of these cell-cell signalling pathways were investigated by the analysis of the spatial distribution of active IGF binding proteins (IGFBP) genes. The IGFBP-3 gene is coexpressed with the IGF-2 gene in proliferative cytotrophoblasts of the embryonic placenta. While active IGFBP-1 and -2 genes in our hands cannot be detected in the embryonic placenta, all three IGFBP genes are expressed in complex and overlapping patterns in the decidua compacta. The results are discussed in terms of how the various IGFBP genes may operate in different cell types to restrict IGF local stimulatory pathways.  相似文献   
22.
Human granulocyte elastase is inhibited by the urinary trypsin inhibitor   总被引:1,自引:0,他引:1  
Two forms of urinary trypsin inhibitor, A and B, were purified from the urine of pregnant women. Form A was the only inhibitor present in fresh urine and inhibitor B arose from degradation of A upon storage of urine. The molecular masses of A and B were about 44 and 20 kDa, respectively, as judged from dodecyl-sulfate polyacrylamide gel electrophoresis, but about 60 kDa and 30 kDa, respectively, as judged from gel filtration analysis. The discrepancy can perhaps be explained by the carbohydrate content amounting to about 10% of each inhibitor. After reduction with mercaptoethanol, inhibitor A and inhibitor B had identical apparent molecular masses of about 20 kDa on dodecyl-sulfate gel electrophoresis. These results and the results of amino acid analysis suggest that one molecule of inhibitor A yields two molecules of inhibitor B. On agarose gel electrophoresis inhibitor A migrated as a rather broad band in the prealbumin region and inhibitor B as 3 well defined bands in the beta-region. Specific antisera were raised against inhibitor A and B. The two inhibitors showed the immunologic reaction of identity with each other and with the plasma inter-alpha-trypsin inhibitor, when using either antiserum. The inhibitors both gave quantitative inhibition of bovine trypsin, the results indicating a 4/1 trypsin/inhibitor molar ratio for A and a 2/1 ratio for B. The two substances also effectively inhibited granulocyte elastase. No inhibition of porcine pancreatic elastase was demonstrable.  相似文献   
23.
Using two cytological methods based on nuclear morphology, quinacrine dihydrochloride (QDH) staining and premature chromosome condensation (PCC), it has been possible to identify cell cyle positions within G1 of growing and arrested 3T3 cells. The fluorescent intensity of QDH-stained interphase cells appears to decrease as the cells pass from mitosis to S phase. Likewise, the length and thickness of prematurely condensed chromatids can be related to the cells' position within the G1 period. Data are presented that deal with three interrelated topics: (1) We determined by fluorometric measurements of nuclei from 3T3 cells that the visual observation of the decrease in QDH fluorescence during G1 reflects an actual decrease in total fluorescence and not a dispersion of the fluorescent chromatin in a larger nuclear area. (2) We correlated the results obtained by QDH staining with those of PCC on the same cell samples blocked in G1 by different conditions. Serum-starved and contact-inhibited cell nuclei had the highest intensity, hydroxyurea-treated ones had the lowest intensity, while that of isoleucine-deprived cells was in between. The same relative order of G1 positions was obtained based on PCC morphology. Thus, both methods monitor the state of chromatin condensation and can be used to identify cell cycle position within G1.(3) We showed with both methods that the states of chromatin resulting from the various G1 blocking conditions differ from each other.  相似文献   
24.
The activation of canine anionic and cationic trypsinogen by enterokinase, trypsin, thrombin, plasmin and extracts from canine granulocytes were studied in vitro. Enterokinase activates both trypsinogens about 1000 times faster than trypsin. The enterokinase-catalyzed activation is not inhibited by the main serum protease inhibitors, alpha-macroglobulin and alpha 1-antitrypsin. alpha-Macroglobulin cannot inhibit the activation of the trypsinogens by trypsin but this reaction is completely inhibited by alpha 1-antitrypsin. The results are discussed in relation to the pathogenesis of acute pancreatitis.  相似文献   
25.
Summary Localization of chromosome breaks in human chromosomes was analyzed in 264 peripheral lymphocyte cultures. Three hundred and sixty-nine chromosome breaks could be exactly localized to a chromosome band or region of the Paris Conference nomenclature. The distribution of breaks in the chromosome regions was found to be nonrandom. Chromosome 3 alone had 23% of the breaks and region 3p2 had 13% of the total breaks. Some other chromosome regions, such as 5p1, 9q1, 14q2, and 16q2 also displayed clustering of breaks. Sex chromosomes had less breaks than expected. Spontaneous chromosome breaks were almost exclusively located in the lightly stained G bands.Supported by grants from the Foundation for Pediatric Research and Research Foundation of Orion Corporation Ltd.  相似文献   
26.
27.
28.
Ecological processes in food webs depend on species interactions. By identifying broad‐scaled interaction patterns, important information on species' ecological roles may be revealed. Here, we use the group model to examine how spatial resolution and proximity influence group structure. We examine a data set from the Barents Sea, with food webs described for both the whole region and 25 subregions. We test how the group structure in the networks differ comparing (1) the regional metaweb to subregions and (2) subregion to subregion. We find that more than half the species in the metaweb change groups when compared to subregions. Between subregions, networks with similar group structure are spatially related. Interestingly, although species overlap is important for similarity in group structure, there are notable exceptions. Our results highlight that species ecological roles vary depending on fine‐scaled differences in the patterns of interactions, and that local network characteristics are important to consider.  相似文献   
29.
Journal of Physiology and Biochemistry - The cardioprotective activity of rosuvastatin (R) is yet to be known. The objective of this study was to research whether R perfusion before global ischemia...  相似文献   
30.
The CYP1A1 gene encoding for an enzyme involved in the metabolic activation of important tobacco carcinogens could be implicated in smoking-induced lung cancer. Given the strong association between tobacco smoking and lung cancer, the effect of tobacco smoke exposure has to be taken into account when studying the potential association between lung cancer and CYP1A1 genotypes. The effect of two CYP1A1 genetic polymorphisms (Mspl and IIe-Val) on lung cancer risk were evaluated using peripheral blood DNA from 150 lung cancer patients and 171 controls. The Mspl sitepresent allele was found among 19.3% of both cases and controls and the variant allele Val among 6.7% of cases and 8.8% of controls. Lung cancer risks associated with the Mspl site-present allele (OR= 0.9; 95%Cl: 0.5-1.8) or with the Val allele (OR= 0.8; 95%Cl: 0.3-1.9) were not increased after adjustment for tobacco and asbestos exposures. These results persisted when analyses were stratified on smoking status, daily consumption of tobacco or duration of smoking. Similar findings were obtained when squamous cell or small cell carcinomas were studied separately. This study thus suggests a minor role for the known CYP1A1 gene polymorphisms in predisposition to lung cancer among Caucasian populations.  相似文献   
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