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   392篇
  免费   16篇
  国内免费   7篇
  2023年   3篇
  2020年   8篇
  2019年   10篇
  2018年   4篇
  2017年   6篇
  2016年   6篇
  2015年   9篇
  2014年   13篇
  2013年   32篇
  2012年   12篇
  2011年   10篇
  2010年   7篇
  2009年   17篇
  2008年   16篇
  2007年   8篇
  2006年   23篇
  2005年   9篇
  2004年   17篇
  2003年   16篇
  2002年   17篇
  2001年   9篇
  2000年   5篇
  1999年   7篇
  1998年   6篇
  1997年   8篇
  1996年   9篇
  1995年   14篇
  1994年   7篇
  1993年   6篇
  1992年   6篇
  1991年   9篇
  1990年   8篇
  1989年   8篇
  1988年   9篇
  1987年   4篇
  1986年   2篇
  1985年   7篇
  1984年   3篇
  1983年   4篇
  1982年   2篇
  1981年   4篇
  1980年   7篇
  1979年   9篇
  1978年   2篇
  1977年   5篇
  1976年   2篇
  1975年   2篇
  1973年   3篇
  1972年   1篇
  1971年   2篇
排序方式: 共有415条查询结果,搜索用时 15 毫秒
71.
对最近分离到的一株能合成维生素C前体 - 2 -酮基 -L -古龙酸 (2 -KGA)的新产酸菌V6生物学和分子生物学特性进行了初步研究。该菌株为革兰氏阴性菌 ,细胞为短杆状 ,菌体大小为 0 .8- 1.0× 0 .4 - 0 .6 μm ,菌落为淡黄色 ,好氧 ,最适生长温度为 2 8~ 30℃ ,最适pH为 7.0~ 7.8,GCmol%含量为 5 3.1% ,不含质粒 ,能氧化葡萄糖、山梨醇和山梨糖合成 2 -KGA。 16SrDNA同源性分析发现 ,该产酸菌与以前报道的能合成 2 -KGA的三个属Ketogulonigenium属、Gluconobacter属和Acetobacter属的同源性分别是 98.9~ 99.3%、82~ 83%和 81~ 82 %。基于以上特性分析 ,该产酸菌在分类发育学上宜归为Ketogulonigenium属。  相似文献   
72.
73.
74.
Two novel brackish water urostyloid ciliates, Anteholosticha paramanca sp. n. and Antiokeronopsis flava gen. n., sp. n., isolated from the Shenzhen Mangrove Nature Protection Area on the coast of the South China Sea, were investigated using live observation and protargol impregnation techniques. Anteholosticha paramanca sp. n. is characterized by its spherical yellowish cortical granules arranged in lines, shortened midventral complex and three transverse cirri. Morphogenesis is similar to that in Anteholosticha manca. The new genus Antiokeronopsis is diagnosed by having a continuous adoral zone of membranelles, frontal cirri arranged in a bicorona, midventral complex composed of midventral pairs only, one marginal cirral row on each side, the presence of frontoterminal and transverse cirri, and the lack of buccal and caudal cirri. The type species A. flava sp. n. is characterized by its elongated body shape, brown to yellowish body color and two types of cortical granules. Small subunit ribosomal RNA gene sequence data justify the classification of both species. Phylogenetic analyses indicate that A. paramanca clusters with Bakuella subtropica within a clade that includes two other Anteholosticha species, while Antiokeronopsis groups within the core urostylids and is most closely related to the well‐known genera Pseudokeronopsis and Uroleptopsis.  相似文献   
75.
Fossil testudinids are known in Europe since the Eocene, with several taxa of medium size (from more than 0.3 m to less than 0.7 m) recognized in the Palaeogene record, most of them being poorly known. The size of several European Neogene taxa was larger (between 1 and 2 m). These large testudinids were relatively abundant and diverse, ranging from the early Miocene to the Pleistocene. However, there is a nomenclatural gap at the generic level for the Neogene forms, as their generally used assignment to the more primitive Eocene Cheirogaster cannot be sustained. This is because relatively little material has been assigned to the described species, and also because of the absence of a detailed study comparing all of the European taxa. Here, the European Cenozoic taxa are incorporated for the first time in a data matrix, so that a hypothesis on their phylogenetic relationships is justified. This study identified the large testudinids from the Neogene of Europe as belonging to a monophyletic clade, assigned to the new genus T itanochelon . The hitherto poorly understood ‘Testudobolivari, proposed nearly a century ago but lacking diagnosis, is analysed in detail. It is recognized as the best‐represented large testudinid from the European record, and is identified as the type species of T itanochelon gen. nov. Its comparison with the other Neogene species allowed a detailed study of the new genus and an analysis of its phylogenetic relationships with the other European taxa. © 2014 The Linnean Society of London  相似文献   
76.
长穗颈双低温敏核不育水稻的选育   总被引:22,自引:4,他引:18  
双低温敏核不育水稻 (96- 5- 2 S)干种子通过 350 Gy60 Coγ-射线直接辐射 ,处理后的 M1代在育性转换敏感期让其感受自然低温而自交繁殖 .M2 代单本或双本密插 (1 0× 1 3.33cm) ,从 M2 代 2 5万株群体中 ,筛选出 7株长穗颈双低温敏核不育株 .它的成功选育 ,解决了我国两系杂交水稻的制种中不育系育性易出现反复和九二 Ο施用量大的两大技术难题  相似文献   
77.
Summary A new species and genus of mousebird (Coliiformes: Coliidae) from the Oligocene (Rupelian) of Frauenweiler near Wiesloch (Baden-Württemberg, Germany) is described.Oligocolius brevitarsus n. gen. n. sp. is the first Oligocene mousebird and one of the most complete skeletons of early Tertiary Coliidae to have come to light so far. The new taxon has a more strongly developed wing and a much shorter tarsometatarsus than recent mousebirds and was probably adapted to a more sustained flight.
Ein neuer Mausvogel (Coliiformes: Coliidae) aus dem Oligozän Deutschlands
Zusammenfassung Eine neue Gattung und Art der Mausvögel (Coliiformes: Coliidae) wird aus dem Oligozän (Rupel) von Frauenweiler bei Wiesloch (Baden-Württemberg, Deutschland) beschrieben.Oligocolius brevitarsus n. gen. n. sp. ist der erste oligozäne Mausvogel und eines der vollständigsten Skelette frühtertiärer Coliidae, das bisher gefunden wurde. Das neue Taxon hat einen kräftiger entwickelten Flügel und einen viel kürzeren Tarsometatarsus als rezente Mausvögel und war wahrscheinlich an einen Flug angepaßt, der ausdauernder als bei rezenten Arten war.
  相似文献   
78.
A new genus and new species of the family Cletopsyllidae Huys & Willems, 1989 from deep-sea sediment in the Gulf of Mexico, are reported and fully described and illustrated. The new genus Pentacletopsyllus (type species: P. montagni sp. n.) can be distinguished from the four known genera of the family by antennule segmentation, length ratio of first and second endopodal segments of P1, and armature pattern on P5 exopod. It also differs from its sister genera by the rostrum being bifid at the tip, third segment of the female antennule having a smooth posterior margin, the baseoendopod of P5 with biarticulate outer setophore bearing basal seta, and female caudal rami without lobate expansion. A revised key to species of the family Cletopsyllidae Huys & Willems, 1989 is provided.  相似文献   
79.
80.
In this paper a new taxon of Kuehneotheriidae is described and diagnosed, mainly by comparison with the genus Kuehneotherium . By its greater age and its more primitive evolutionary state, Woutersia mirabilis gen. et sp. nov. is a particularly interesting element of the fauna and enlarges the concept of the Kuehneotheriidae.
Dans cet article est dAecrit et défini un nouveau taxon de Kuehneotheriidés, Woutersia mirabilis gen. et sp. nov., par comparaison avec Kuehneotherium . Son âge plus ancien et son stade évolution considéré comme plus primitif en font un élément particuliérement intéressant, qui élargit en outre le concept des Kuehneotheriidés.  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