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   666篇
  免费   2篇
  国内免费   6篇
系统科学   5篇
丛书文集   1篇
教育与普及   3篇
理论与方法论   27篇
现状及发展   216篇
研究方法   79篇
综合类   321篇
自然研究   22篇
  2018年   5篇
  2017年   8篇
  2016年   9篇
  2015年   4篇
  2014年   5篇
  2013年   7篇
  2012年   32篇
  2011年   49篇
  2010年   17篇
  2009年   5篇
  2008年   15篇
  2007年   20篇
  2006年   28篇
  2005年   14篇
  2004年   35篇
  2003年   30篇
  2002年   19篇
  2001年   23篇
  2000年   24篇
  1999年   19篇
  1996年   4篇
  1995年   3篇
  1992年   10篇
  1991年   6篇
  1990年   8篇
  1989年   10篇
  1988年   10篇
  1987年   7篇
  1986年   8篇
  1985年   12篇
  1984年   10篇
  1983年   8篇
  1982年   8篇
  1981年   3篇
  1980年   13篇
  1979年   14篇
  1978年   12篇
  1977年   14篇
  1976年   6篇
  1975年   13篇
  1974年   22篇
  1973年   12篇
  1972年   9篇
  1971年   6篇
  1970年   13篇
  1969年   10篇
  1968年   12篇
  1967年   9篇
  1966年   12篇
  1965年   7篇
排序方式: 共有674条查询结果,搜索用时 171 毫秒
101.
Absolute configuration of the prostaglandins   总被引:4,自引:0,他引:4  
  相似文献   
102.
Correlation of cell shape and function in the visual cortex of the cat   总被引:1,自引:0,他引:1  
D Van Essen  J Kelly 《Nature》1973,241(5389):403-405
  相似文献   
103.
104.
105.
106.
All cancers carry somatic mutations in their genomes. A subset, known as driver mutations, confer clonal selective advantage on cancer cells and are causally implicated in oncogenesis, and the remainder are passenger mutations. The driver mutations and mutational processes operative in breast cancer have not yet been comprehensively explored. Here we examine the genomes of 100 tumours for somatic copy number changes and mutations in the coding exons of protein-coding genes. The number of somatic mutations varied markedly between individual tumours. We found strong correlations between mutation number, age at which cancer was diagnosed and cancer histological grade, and observed multiple mutational signatures, including one present in about ten per cent of tumours characterized by numerous mutations of cytosine at TpC dinucleotides. Driver mutations were identified in several new cancer genes including AKT2, ARID1B, CASP8, CDKN1B, MAP3K1, MAP3K13, NCOR1, SMARCD1 and TBX3. Among the 100 tumours, we found driver mutations in at least 40 cancer genes and 73 different combinations of mutated cancer genes. The results highlight the substantial genetic diversity underlying this common disease.  相似文献   
107.
Medulloblastoma, the most common malignant paediatric brain tumour, arises in the cerebellum and disseminates through the cerebrospinal fluid in the leptomeningeal space to coat the brain and spinal cord. Dissemination, a marker of poor prognosis, is found in up to 40% of children at diagnosis and in most children at the time of recurrence. Affected children therefore are treated with radiation to the entire developing brain and spinal cord, followed by high-dose chemotherapy, with the ensuing deleterious effects on the developing nervous system. The mechanisms of dissemination through the cerebrospinal fluid are poorly studied, and medulloblastoma metastases have been assumed to be biologically similar to the primary tumour. Here we show that in both mouse and human medulloblastoma, the metastases from an individual are extremely similar to each other but are divergent from the matched primary tumour. Clonal genetic events in the metastases can be demonstrated in a restricted subclone of the primary tumour, suggesting that only rare cells within the primary tumour have the ability to metastasize. Failure to account for the bicompartmental nature of metastatic medulloblastoma could be a major barrier to the development of effective targeted therapies.  相似文献   
108.
Van Noorden R 《Nature》2012,483(7388):134-135
  相似文献   
109.
Van Noorden R 《Nature》2012,483(7389):S32-S33
  相似文献   
110.
The vortex state, characterized by a curling magnetization, is one of the equilibrium configurations of soft magnetic materials and occurs in thin ferromagnetic square and disk-shaped elements of micrometre size and below. The interplay between the magnetostatic and the exchange energy favours an in-plane, closed flux domain structure. This curling magnetization turns out of the plane at the centre of the vortex structure, in an area with a radius of about 10 nanometres--the vortex core. The vortex state has a specific excitation mode: the in-plane gyration of the vortex structure about its equilibrium position. The sense of gyration is determined by the vortex core polarization. Here we report on the controlled manipulation of the vortex core polarization by excitation with small bursts of an alternating magnetic field. The vortex motion was imaged by time-resolved scanning transmission X-ray microscopy. We demonstrate that the sense of gyration of the vortex structure can be reversed by applying short bursts of the sinusoidal excitation field with amplitude of about 1.5 mT. This reversal unambiguously indicates a switching of the out-of-plane core polarization. The observed switching mechanism, which can be understood in the framework of micromagnetic theory, gives insights into basic magnetization dynamics and their possible application in data storage.  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