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   5004篇
  免费   239篇
  国内免费   704篇
  2023年   73篇
  2022年   92篇
  2021年   127篇
  2020年   132篇
  2019年   159篇
  2018年   182篇
  2017年   139篇
  2016年   139篇
  2015年   158篇
  2014年   228篇
  2013年   365篇
  2012年   214篇
  2011年   182篇
  2010年   181篇
  2009年   223篇
  2008年   248篇
  2007年   202篇
  2006年   163篇
  2005年   172篇
  2004年   180篇
  2003年   129篇
  2002年   185篇
  2001年   169篇
  2000年   182篇
  1999年   139篇
  1998年   116篇
  1997年   114篇
  1996年   88篇
  1995年   82篇
  1994年   92篇
  1993年   106篇
  1992年   94篇
  1991年   84篇
  1990年   63篇
  1989年   36篇
  1988年   40篇
  1987年   43篇
  1986年   32篇
  1985年   65篇
  1984年   60篇
  1983年   43篇
  1982年   77篇
  1981年   59篇
  1980年   52篇
  1979年   43篇
  1978年   42篇
  1977年   43篇
  1976年   42篇
  1975年   24篇
  1973年   16篇
排序方式: 共有5947条查询结果,搜索用时 15 毫秒
101.
Thirty-two Borrelia isolates were obtained from the adult stage of ixodid ticks, Ixodes ovatus, collected in various localities in Japan. Borrelial isolates were cultivated and analyzed by polyacrylamide gel electrophoresis, with monoclonal antibodies, by pulsed field gel electrophoresis, and by genomic Southern hybridization. All borrelial isolates showed similar protein profiles and monoclonal antibody reactivities, while plasmid profiles were rather diverse. Genomic hybridization using rRNA gene probes demonstrated the genetic similarities of those isolates. We found no significant differences among the borrelial isolates tested, and the restriction fragment length polymorphism patterns of I. ovatus isolates were quite distinct from those of borrelial strains associated with Lyme disease. Therefore, the isolates of Borrelia obtained from I. ovatus were thought to fall into different genospecies.  相似文献   
102.
103.
Abstract: There are three major breeding populations of southern elephant seals centered on Macquarie Island, Kerguelen-Heard Islands and South Georgia-Antarctic Peninsula. The composition of the diet differs between these populations based on published data from Signy Island and data presented here from Macquarie and Heard Islands. These differences in diet appear to be linked to the location at which seals were sampled ranging from the least Antarctic (Macquarie Island) to the most Antarctic (Signy Island). The major food remains consisted of cephalopod beaks and fish eye lenses. More benthic material was found at Heard Island than at Macquarie Island. The diet at Macquarie Island differed between summer and winter and between young animals and adults. The difficulty in collecting dietary samples of southern elephant seals near their main foraging areas makes the study of the feeding ecology of this species extremely difficult in comparison with other Southern Ocean species.  相似文献   
104.
The continental coasts and remote islands in the high-latitude Southern Hemisphere, including the subantarctic region, are characterized by many endemic species, high abundance of taxa, and intermediate levels of biodiversity. The macroalgal flora of these locations has received relatively little attention. Filamentous green algae are prolific in the intertidal of southern islands, but the taxonomy, distribution, and evolutionary history of these taxa are yet to be fully explored, mostly due to the difficulty of access to some of these locations. In this study, we examined specimens of the order Cladophorales from various locations in the high-latitude Southern Hemisphere including the subantarctic (the Auckland Islands, Bounty Islands, Campbell Island, Macquarie Island, and Kerguelen Islands), as well as mainland New Zealand, the Chatham Islands, Chile, and Tasmania. The analyses of the rDNA sequences of the samples revealed the existence of two new clades in a phylogeny of the Cladophoraceae. One of these clades is described as the novel genus Vandenhoekia gen. nov., which contains three species that are branched or unbranched. The amended genus Rama is reinstated to accommodate the other clade, and contains four species, including the Northern Hemisphere “Cladophora rupestris.” In Rama both branched and unbranched morphologies are found. It is remarkable that gross morphology is not a predictor for generic affiliations in these algae. This study illustrates that much can still be learned about diversity in the Cladophorales and highlights the importance of new collections, especially in novel locations.  相似文献   
105.
2021年8月,在安徽省合肥市庐江县牛王寨采集到东亚腹链蛇属(Hebius)蛇类标本1号。经形态比较发现,该蛇明显不同于大别山地区已有的东亚腹链蛇属物种——棕黑腹链蛇(H. sauteri)和绣链腹链蛇(H. craspedogaster)。分子系统学分析显示,该标本与东亚腹链蛇(H. vibakari)遗传关系最近,且形态上符合东亚腹链蛇特征,提示该标本应为东亚腹链蛇。东亚腹链蛇是安徽省和大别山地区爬行动物分布新记录种,这也是该物种在中国东北地区之外首次被报道。该分布新记录扩大了对东亚腹链蛇的分布范围的认知,对东亚腹链蛇的种群分化和生物地理学研究具有重要意义。  相似文献   
106.
云开脊蛇(Achalinus yunkaiensis)之前仅在广东和广西有分布报道。本文基于形态比较及线粒体COI基因序列分子系统关系分析结果,确定采集于湖南省新宁县的1号雌性脊蛇标本(CIB 119041)为云开脊蛇,为湖南省新记录种。该标本鼻间鳞沟约等于前额鳞沟,上颔齿24枚;背鳞通身23行,腹鳞150枚,尾下鳞55枚;尾长与体长之比为0.203。至此共有4种脊蛇分布于湖南省。此外,本文还报道了棕脊蛇(A. rufescens)1号雄性地模标本(CIB 119042),该标本鼻间鳞沟长于前额鳞沟;背鳞通身23行,腹鳞153枚,尾下鳞62枚;尾长与体长之比0.201。分子系统发育结果显示,棕脊蛇种组各支系的系统地位还需进一步研究厘定。  相似文献   
107.
2021年7月在四川省宜宾市筠连县大雪山风景区乌岭沟东北(27°53′N,104°45′E,海拔1 380 m)采集到2号角蟾科(Megophryidae)布角蟾属(Boulenophrys)物种标本(标本号:WG202107005和WG202107006)。通过形态学比较并基于线粒体16S rRNA和细胞色素氧化酶亚基I(COI)基因序列构建的最大似然树显示,2号标本是黔北角蟾(B. qianbeiensis)。目前,已知黔北角蟾分布于贵州省桐梓县黄连自然保护区和贵州省宽阔水国家级自然保护区,此次在四川宜宾发现黔北角蟾确定为四川省两栖类分布新记录种。  相似文献   
108.
2022年8月,于湖南省郴州市永兴县湘阴渡镇(113°01′18′′E,26°11′87′′N,海拔174 m)采集到两头蛇活体标本1号,通过形态测量比较,发现所采集标本与中国广东省分布的岭南两头蛇(Calamariaarcana)形态特征基本一致;后基于线粒体Cytb基因片段进行分子系统发育分析,结果显示该标本与岭南两头蛇形成高支持率单系群(后验概率PP为1.00,自举值BS为100),所采集标本与岭南两头蛇的遗传距离为1%。综合形态学和分子生物学证据,最终确定该标本为两头蛇科(Calamariidae)两头蛇属的岭南两头蛇,系湖南省蛇类分布新记录种。  相似文献   
109.
A coracoid of an enantiornithine bird from Upper Cretaceous (probably late Campanian) fluvial sediments at Castigno (Villespassans, Hérault, southern France) is described. It differs from all hitherto reported enantiornithine coracoids and is referred a new genus and species, Castignovolucris sebei. This bone is large and robust, indicating a bird that was among the largest known enantiornithines, possibly the size of a Canada Goose (Branta canadensis). The new taxon is an addition to the short list of Late Cretaceous birds from France and confirms that enantiornithines were an important component of European avifaunas until late in the Cretaceous.  相似文献   
110.
横脊叶蝉科一新记录属及一新种:(同翅目:叶蝉总科)   总被引:1,自引:1,他引:0  
本文记述分布在贵州的横脊叶蝉科1新记录属及1新种。模式标本保存在贵州农学院。 弯头叶蝉属Vangama Distant 1907中国新记录属 本属最显著的特征是头冠部向前极度延长突出,其长度约与后足胫节等长,端部向上弯曲,中央有1明显纵脊;颜面长大于宽,适度隆起,中央有1显著的纵脊;单眼位于头冠侧缘,着生在复眼前域。前胸背板宽大于长,中城隆起,向两侧斜倾,前缘弧圆突出,后缘微凹;小盾片宽三角形,微短于前胸背板;前翅狭长,爪片宽大,具4个端室。  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