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   43765篇
  免费   2303篇
  国内免费   548篇
  2023年   177篇
  2022年   243篇
  2021年   862篇
  2020年   544篇
  2019年   652篇
  2018年   1414篇
  2017年   1242篇
  2016年   1789篇
  2015年   3072篇
  2014年   3412篇
  2013年   3013篇
  2012年   2811篇
  2011年   2842篇
  2010年   2324篇
  2009年   1844篇
  2008年   2053篇
  2007年   1874篇
  2006年   1805篇
  2005年   1749篇
  2004年   1804篇
  2003年   1341篇
  2002年   1163篇
  2001年   812篇
  2000年   706篇
  1999年   592篇
  1998年   426篇
  1997年   400篇
  1996年   318篇
  1995年   304篇
  1994年   198篇
  1993年   496篇
  1992年   506篇
  1991年   382篇
  1990年   291篇
  1989年   308篇
  1988年   271篇
  1987年   234篇
  1986年   211篇
  1985年   255篇
  1984年   149篇
  1983年   94篇
  1982年   88篇
  1981年   92篇
  1980年   95篇
  1979年   112篇
  1978年   95篇
  1977年   78篇
  1976年   77篇
  1974年   72篇
  1973年   75篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
41.
42.
Severe aortic valve stenosis (AVS) and mitral valve regurgitation (MVR) often coexist. Although a fully percutaneous treatment for the two conditions, by means of transcatheter aortic valve implantation (TAVI) followed by MitraClip, can be appealing in selected high-risk candidates, critical and strategical reasoning should be applied. In a 3-year period we have developed a single-centre experience of 14 patients who were managed with a staged percutaneous approach to treat severe AVS and MVR. The average interval from TAVI to MitraClip repair was 101 ± 12 days. Success for TAVI was 100% and 92.9% (13/14) for MitraClip. At late follow-up, 3 patients developed MVR 3+. Estimated 1?year survival was 66.5%. Freedom from 1?year endpoint (death, stroke, major bleeding, myocardial infarction, and cardiac re-hospitalisation) was 57.9%.In our view, a fully transcatheter approach for mitro-aortic pathology is feasible and should be performed only as a staged procedure in those patients that remain symptomatic, in spite of successful TAVI. It should be emphasised that although the periprocedural success rate is satisfactory, follow-up mortality and re-hospitalisation rates remain high, even at mid-term follow-up. This most probably results from the advanced clinical picture at time of referral for treatment.  相似文献   
43.
44.
45.
46.
Media, and particularly TV media, have a great impact on the general public. In recent years, spatial patterns of information and the relevance of intangible geographies have become increasingly important. Gatekeeping plays a critical role in the selection of information that is transformed into media. Therefore, gatekeeping, through national media, also co-forms the generation of mental maps. In this paper, correspondence analysis (a statistical method) combined with cloud lines (a new visual analytics technique) is used to analyze how individual major regional events in one of the post-communist countries, the Czech Republic, penetrate into the media on a national scale. Although national news should minimize distortions about regions, this assumption has not been verified by our research. Impressions presented by the media of selected regions that were markedly influenced by one or several events in those regions demonstrate that gatekeepers, especially news reporters, functioned as a filter by selecting only a few specific, and in many cases, unusual events for dissemination.  相似文献   
47.
48.
Reviewed are works concerning the mechanisms of collagen (type I) fibril packing and the influence of macromolecular structure and physicochemical parameters of the medium on the process.  相似文献   
49.
Cytokinesis must be initiated only after chromosomes have been segregated in anaphase and must be terminated once cleavage is completed. We show that the fission yeast protein Etd1 plays a central role in both of these processes. Etd1 activates the guanosine triphosphatase (GTPase) Spg1 to trigger signaling through the septum initiation network (SIN) pathway and onset of cytokinesis. Spg1 is activated in late anaphase when spindle elongation brings spindle pole body (SPB)–localized Spg1 into proximity with its activator Etd1 at cell tips, ensuring that cytokinesis is only initiated when the spindle is fully elongated. Spg1 is active at just one of the two SPBs during cytokinesis. When the actomyosin ring finishes constriction, the SIN triggers disappearance of Etd1 from the half of the cell with active Spg1, which then triggers Spg1 inactivation. Asymmetric activation of Spg1 is crucial for timely inactivation of the SIN. Together, these results suggest a mechanism whereby cell asymmetry is used to monitor cytoplasmic partitioning to turn off cytokinesis signaling.  相似文献   
50.
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