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   60180篇
  免费   4476篇
  国内免费   13篇
  2023年   404篇
  2022年   641篇
  2021年   1425篇
  2020年   1009篇
  2019年   1305篇
  2018年   1842篇
  2017年   1630篇
  2016年   2303篇
  2015年   2938篇
  2014年   3197篇
  2013年   4250篇
  2012年   5070篇
  2011年   4948篇
  2010年   3062篇
  2009年   2530篇
  2008年   3493篇
  2007年   3289篇
  2006年   3127篇
  2005年   2654篇
  2004年   2566篇
  2003年   2405篇
  2002年   2106篇
  2001年   964篇
  2000年   1014篇
  1999年   759篇
  1998年   525篇
  1997年   397篇
  1996年   363篇
  1995年   338篇
  1994年   282篇
  1993年   284篇
  1992年   315篇
  1991年   286篇
  1990年   252篇
  1989年   206篇
  1988年   190篇
  1987年   194篇
  1986年   173篇
  1985年   176篇
  1984年   177篇
  1983年   144篇
  1982年   140篇
  1981年   121篇
  1980年   98篇
  1979年   112篇
  1978年   95篇
  1977年   78篇
  1975年   68篇
  1974年   84篇
  1973年   69篇
排序方式: 共有10000条查询结果,搜索用时 241 毫秒
51.
Carcinoma tissue consists of not only tumor cells but also fibroblasts, endothelial cells or vascular structures, and inflammatory cells forming the supportive tumor stroma. Therefore, the spatial distribution of proteins that promote growth and proliferation in these complex functional units is of high interest. Matrix-assisted laser desorption/ionization imaging mass spectrometry is a newly developed technique that generates spatially resolved profiles of protein signals directly from thin tissue sections. Surface-enhanced laser desorption/ionization mass spectrometry (MS)combined with tissue microdissection allows analysis of defined parts of the tissue with a higher sensitivity and a broader mass range. Nevertheless, both MS-based techniques have a limited spatial resolution. IHC is a technique that allows a resolution down to the subcellular level. However, the detection and measurement of a specific protein expression level is possible only by semiquantitative methods. Moreover, prior knowledge about the identity of the proteins of interest is necessary. In this study, we combined all three techniques to gain highest spatial resolution, sensitivity, and quantitative information. We used frozen tissue from head and neck tumors and chose two exemplary proteins (HNP1–3 and S100A8) to highlight the advantages and disadvantages of each technique. It could be shown that the combination of these three techniques results in congruent but also synergetic data. (J Histochem Cytochem 58:929–937, 2010)  相似文献   
52.
53.
Evidence that the learning gains of preschool fade as children transition into elementary school has led to increased efforts to sustain preschool advantages during this key transitional period. This study explores whether the observed benefits of sustainability practices for a range of child outcomes are explained and/or moderated by family and school mechanisms selecting children into experiencing these practices. Analyses of the Early Childhood Longitudinal Study-Birth Cohort revealed that both family and school factors predicted children’s exposure to several PK-3 sustainability practices. PK-3 sustainability practices were associated with reading (but not math) gains and better interpersonal skills (but not fewer externalizing behaviors) following the transition into kindergarten. These links were not conditioned by the selection mechanisms. The findings highlight who is more likely to seek out (at the family level) or offer (at the school level) sustainability practices and how relevant they are to fighting preschool fadeout.  相似文献   
54.
55.
56.
Hela cells were impregnated with silver according to Paweletz et al. (1967). In cells in mitosis not only the nucleolar organizer regions (NORs) are strongly impregnated but also part of the nucleolar material, which accumulates in and around the chromosomes. The treatment with adenosine, which in interphase cells spreads the nucleolar material within the nucleus, also distributes the argentophilic material in and around the chromosomes. During the reconstruction phase this material reassembles around the NORs to form parts of the new nucleolus. The silver impregnation technique clearly demonstrates that two main components are responsible for the argentophily of the nucleolus. This is in agreement with the results obtained by Lischwe et al. (1979).  相似文献   
57.
Further studies on theisfA mutation responsible for anti-SOS and antimutagenic activities inEscherichia coli are described. We have previously shown that theisfA mutation inhibits mutagenesis and other SOS-dependent phenomena, possibly by interfering with RecA coprotease activity. TheisfA mutation has now been demonstrated also to suppress mutator activity inE. coli recA730 andrecA730 lexA51(Def) strains that constitutively express RecA coprotease activity. We further show that the antimutator activity of theisfA mutation is related to inhibition of RecA coprotease-dependent processing of UmuD. Expression of UmuD' from plasmid pGW2122 efficiently restores UV-induced mutagenesis in therecA730 isfA strain and partially restores its mutator activity. On the other hand, overproduction of UmuD'C proteins from pGW2123 plasmid markedly enhances UV sensitivity with no restoration of mutability.  相似文献   
58.
A new assay procedure for phenol sulfotransferase which employs [35S]-3'-phosphoadenosine-5'-phosphosulfate as a sulfate donor and a variety of phenols as sulfate acceptors was developed. The appearance of the 35S-sulfated products or the disappearance of the [35S]-3'-phosphoadenosine-5'-phosphosulfate are determined simultaneously by chromatography of the assay incubation mixtures on Ecteola-cellulose columns, eluting with an NH4HCO3 step gradient. Various acidic, neutral, and basic phenols can be employed as substrates for phenol sulfotransferase using this procedure.  相似文献   
59.
60.
Death certification should be able to provide accurate data on the number of deaths due to AIDS as a basis for predicting future deaths from the syndrome. Trends in deaths from other causes may identify conditions that have not been recognised to be associated with HIV infection. Mortality statistics with reference to AIDS in England and Wales were completed from death certificates. Increases in deaths from selected causes likely to be associated with AIDS or HIV infection suggested that in some patients with HIV infection, AIDS was not stated on the death certificate or subsequently notified by the doctor who signed the certificate. From calculations of excess deaths between the beginning of 1985 and the end of April 1987, compared with 1984 at least 495 deaths possibly associated with HIV infection were estimated to have occurred among men aged 15-54 during that period. In 261 AIDS or HIV infection was stated on the original or amended death entry as the cause of death, and of these 198 were included in the estimated number of excess deaths.Accurate notification of the underlying cause of death and associated diseases is required for the precise monitoring of trends in mortality from AIDS and possible identification of unrecognised conditions associated with HIV infection.  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