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   5055篇
  免费   466篇
  国内免费   11篇
  2023年   25篇
  2022年   55篇
  2021年   124篇
  2020年   65篇
  2019年   82篇
  2018年   129篇
  2017年   110篇
  2016年   146篇
  2015年   247篇
  2014年   259篇
  2013年   342篇
  2012年   359篇
  2011年   351篇
  2010年   235篇
  2009年   168篇
  2008年   242篇
  2007年   228篇
  2006年   213篇
  2005年   177篇
  2004年   214篇
  2003年   147篇
  2002年   168篇
  2001年   126篇
  2000年   125篇
  1999年   92篇
  1998年   41篇
  1997年   34篇
  1996年   23篇
  1995年   32篇
  1994年   36篇
  1993年   29篇
  1992年   63篇
  1991年   58篇
  1990年   56篇
  1989年   44篇
  1988年   44篇
  1987年   34篇
  1986年   49篇
  1985年   35篇
  1984年   41篇
  1983年   31篇
  1979年   32篇
  1977年   26篇
  1976年   21篇
  1972年   26篇
  1970年   29篇
  1969年   32篇
  1968年   28篇
  1967年   23篇
  1965年   22篇
排序方式: 共有5532条查询结果,搜索用时 46 毫秒
151.
152.
BackgroundWe compared protection of mycophenolate mofetil (MMF) and azathioprine (AZA) against acute cellular rejection (ACR) and chronic allograft nephropathy (CAN) in kidney transplant recipients on steroid-free, low-dose cyclosporine (CsA) microemulsion maintenance immunosuppression.Methods and findingsATHENA, a pragmatic, prospective, multicenter trial conducted by 6 Italian transplant centers, compared the outcomes of 233 consenting recipients of a first deceased donor kidney transplant induced with low-dose thymoglobulin and basiliximab and randomized to MMF (750 mg twice/day, n = 119) or AZA (75 to 125 mg/day, n = 114) added-on maintenance low-dose CsA microemulsion and 1-week steroid. In patients without acute clinical or subclinical rejections, CsA dose was progressively halved. Primary endpoint was biopsy-proven CAN. Analysis was by intention to treat.Participants were included between June 2007 and July 2012 and followed up to August 2016. Between-group donor and recipient characteristics, donor/recipient mismatches, and follow-up CsA blood levels were similar. During a median (interquartile range (IQR)) follow-up of 47.7 (44.2 to 48.9) months, 29 of 87 biopsied patients on MMF (33.3%) versus 31 of 88 on AZA (35.2%) developed CAN (hazard ratio (HR) [95% confidence interval (CI)]: 1.147 (0.691 to 1.904, p = 0.595). Twenty and 21 patients on MMF versus 34 and 14 on AZA had clinical [HR (95% CI): 0.58 (0.34 to 1.02); p = 0.057) or biopsy-proven subclinical [HR (95% CI): 1.49 (0.76 to 2.92); p = 0.249] ACR, respectively. Combined events [HR (95% CI): 0.85 (0.56 to 1.29); p = 0.438], patient and graft survival, delayed graft function (DGF), 3-year glomerular filtration rate (GFR) [53.8 (40.6;65.7) versus 49.8 (36.8;62.5) mL/min/1.73 m2, p = 0.50], and adverse events (AEs) were not significantly different between groups.Chronicity scores other than CAN predict long-term graft outcome. Study limitations include small sample size and unblinded design.ConclusionsIn this study, we found that in deceased donor kidney transplant recipients on low-dose CsA and no steroids, MMF had no significant benefits over AZA. This finding suggests that AZA, due to its lower costs, could safely replace MMF in combination with minimized immunosuppression.Trial registrationClinicalTrials.gov NCT00494741; EUDRACT 2006-005604-14.

Piero Ruggenenti and co-workers study maintenance immunosuppression in deceased-donor kidney transplantation.  相似文献   
153.
The noise filter hypothesis predicts that species using higher sound frequencies should be more tolerant of noise pollution, because anthropogenic noise is more intense at low frequencies. Recent work analysed continental‐scale data on anthropogenic noise across the USA and found that passerine species inhabiting more noise‐polluted areas do not have higher peak song frequency but have more complex songs. However, this metric of song complexity is of ambiguous interpretation, because it can indicate either diverse syllables or a larger frequency bandwidth. In the latter case, the finding would support the noise filter hypothesis, because larger frequency bandwidths mean that more sound energy spreads to frequencies that are less masked by anthropogenic noise. We reanalysed how passerine song predicts exposure to noise using a more thorough dataset of acoustic song measurements, and showed that it is large frequency bandwidths, rather than diverse syllables, that predict the exposure of species to noise pollution. Given that larger bandwidths often encompass higher maximum frequencies, which are less masked by anthropogenic noise, our result suggests that tolerance to noise pollution might depend mostly on having the high‐frequency parts of song little masked by noise, thus preventing acoustic communication from going entirely unnoticed at long distances.  相似文献   
154.
In Arabidopsis, stamen elongation, which ensures male fertility, is controlled by the auxin response factor ARF8, which regulates the expression of the auxin repressor IAA19. Here, we uncover a role for light in controlling stamen elongation. By an extensive genetic and molecular analysis we show that the repressor of light signaling COP1, through its targets HY5 and HYH, controls stamen elongation, and that HY5 – oppositely to ARF8 – directly represses the expression of IAA19 in stamens. In addition, we show that in closed flower buds, when light is shielded by sepals and petals, the blue light receptors CRY1/CRY2 repress stamen elongation. Coherently, at flower disclosure and in subsequent stages, stamen elongation is repressed by the red and far‐red light receptors PHYA/PHYB. In conclusion, different light qualities – sequentially perceived by specific photoreceptors – and the downstream COP1–HY5/HYH module finely tune auxin‐induced stamen elongation and thus male fertility.  相似文献   
155.
156.
157.
158.
159.

In 1976, the Genetics Society of America (GSA) published a document entitled “Resolution of Genetics, Race, and Intelligence.” This document laid out the Society’s position in the IQ controversy, particularly that on scientific and ethical questions involving the genetics of intellectual differences between human populations. Since the GSA was the largest scientific society of geneticists in the world, many expected the document to be of central importance in settling the controversy. Unfortunately, the Resolution had surprisingly little influence on the discussion. In 1979, William Provine analyzed the possible factors that decreased the impact of the Resolution, among them scientists’ limited understanding of the relationship between science and ethics. Through the analysis of unpublished versions of the Resolution and exchanges between GSA members, I will suggest that the limited impact of the statement likely depended on a shift in the aims of the GSA due to the controversies that surrounded the preparation of the document. Indeed, the demands of the membership made it progressively more impartial in both scientific and political terms, decreasing its potential significance for a wider audience. Notably, the troubled history of the Resolution raises the question of what can make effective or ineffective the communication between scientists and the public—a question with resonance in past and present discussions on topics of social importance.

  相似文献   
160.
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