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   382篇
  免费   19篇
  2023年   4篇
  2021年   5篇
  2020年   6篇
  2019年   6篇
  2018年   4篇
  2017年   8篇
  2016年   6篇
  2015年   12篇
  2014年   9篇
  2013年   14篇
  2012年   15篇
  2011年   12篇
  2010年   13篇
  2009年   12篇
  2008年   12篇
  2007年   11篇
  2006年   11篇
  2005年   10篇
  2004年   13篇
  2003年   8篇
  2002年   10篇
  2001年   6篇
  2000年   4篇
  1999年   38篇
  1998年   51篇
  1997年   41篇
  1996年   2篇
  1995年   3篇
  1992年   3篇
  1991年   3篇
  1990年   2篇
  1989年   2篇
  1988年   10篇
  1987年   4篇
  1985年   3篇
  1984年   2篇
  1983年   2篇
  1982年   2篇
  1980年   2篇
  1977年   3篇
  1975年   1篇
  1974年   1篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
  1967年   1篇
  1966年   2篇
  1965年   1篇
  1964年   1篇
  1950年   1篇
排序方式: 共有401条查询结果,搜索用时 46 毫秒
41.
The liver flukes, Fasciola hepatica and Fasciola gigantica, are considered to be sister species and between them present a major threat worldwide to livestock production. In this study sequence data have been employed from informative regions of the nuclear and mitochondrial genomes of over 200 morphologically F. hepatica-like or F. gigantica-like flukes from Europe, sub-Saharan Africa and South Asia to assess genetic diversity. Evidence is presented for the existence of four well-separated clades: African gigantica-like flukes, Indian gigantica-like flukes, European hepatica-like flukes and African high-altitude hepatica-like flukes. Application of the Biological Species Concept to trematodes is problematic; however, the degree of separation between these groups was sufficient for them to be considered as distinct species using the four times rule for speciation.  相似文献   
42.
The dynamic nature of coral reefs offers a rare opportunity to examine the response of ecosystems to disruption due to climate change. In 1998, the Great Barrier Reef experienced widespread coral bleaching and mortality. As a result, cryptobenthic fish assemblages underwent a dramatic phase-shift. Thirteen years, and up to 96 fish generations later, the cryptobenthic fish assemblage has not returned to its pre-bleach configuration. This is despite coral abundances returning to, or exceeding, pre-bleach values. The post-bleach fish assemblage exhibits no evidence of recovery. If these short-lived fish species are a model for their longer-lived counterparts, they suggest that (1) the full effects of the 1998 bleaching event on long-lived fish populations have yet to be seen, (2) it may take decades, or more, before recovery or regeneration of these long-lived species will begin, and (3) fish assemblages may not recover to their previous composition despite the return of corals.  相似文献   
43.
The majority of authors consider Festuca jubata Lowe as an endemic species common to Madeira and the Azores. Saint-Yves proposed that F. jubata was an Azorean endemic and described a geovicarious taxon in Madeira: F. filiformis C. Sm. ex Link in Buch ssp. mandonii St.-Yves. We undertook a complete bibliographical revision of the taxonomy, nomenclature, and chorology of F. jubata s.l. , and contrasted it with morphological and anatomical studies performed on samples from the Azores and Madeira. Azorean plants usually identified as F. jubata had a character combination distinct from that of those with a Madeiran provenance. Saint-Yves' proposal of two independent taxa was correct, but he erroneously considered F. jubata as an Azorean endemic because the name F. jubata was based on Madeiran plants. Consequently, F. jubata auct. pl. from the Azores belongs to a new species.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 493–499.  相似文献   
44.
Different Spanish unifloral honeys (eucalyptus, sunflower, rosemary, thyme, lavender, citrus, anise, quercus, and lemon blossom) and one multifloral honey were studied by Free-Choice Profiling (FCP) analysis. Generalized Procrustes Analysis (GPA) applied to the FCP data allowed discrimination between samples and provided information on the attributes responsible for the differences observed. The honeys had significantly different sensory characteristics. Textural attributes were the predominant factor in discriminating between samples, and appearance (color included) was also correlated with GPA dimensions to a lesser extent.  相似文献   
45.
In the southern Iberian Peninsula, Rhododendron ponticum occurs in restricted and vulnerable populations as a Tertiary relict. Population structure and the main phases of the reproductive process were examined in order to shed light on recruitment patterns and limitations. Rhododendron ponticum flowers are self-compatible and attract a diverse array of insects, which are responsible for a considerable number of seeds set in the populations. Nevertheless, only adults form populations, whilst seedlings are scarce and saplings virtually absent (only two juveniles out of 2489 adults sampled). Non-specialized vegetative multiplication by layering was observed. Recruitment failure seems to depend on the scarcity of safe microsites, which are free from drought, for seedling establishment. The observations contrast with R. ponticum 's reputation as an aggressive invader in temperate Atlantic areas. It is proposed that the species shows a variable balance between sexual reproduction and vegetative multiplication depending on environmental conditions. At present, only the latter seems to be prevailing in relict populations in the Iberian Peninsula. This flexible reproductive strategy is also discussed as a mechanism allowing persistence during geological climatic oscillations.  © The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 140 , 297–311.  相似文献   
46.
Homeobox proteins as sequence-specific transcription factors   总被引:48,自引:0,他引:48  
M Levine  T Hoey 《Cell》1988,55(4):537-540
  相似文献   
47.
Avian influenza     
J Hoey 《CMAJ》1998,158(3):369
  相似文献   
48.
49.
Editor's preface     
J. Hoey 《CMAJ》1997,157(5):497
  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