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   199篇
  免费   20篇
  国内免费   2篇
  2024年   1篇
  2023年   5篇
  2022年   4篇
  2021年   8篇
  2020年   18篇
  2019年   9篇
  2018年   11篇
  2017年   9篇
  2016年   7篇
  2015年   7篇
  2014年   6篇
  2013年   14篇
  2012年   14篇
  2011年   12篇
  2010年   6篇
  2009年   5篇
  2008年   5篇
  2007年   5篇
  2006年   6篇
  2005年   11篇
  2004年   1篇
  2003年   11篇
  2002年   2篇
  2001年   4篇
  2000年   3篇
  1999年   3篇
  1998年   3篇
  1997年   3篇
  1996年   4篇
  1995年   4篇
  1994年   5篇
  1993年   1篇
  1992年   4篇
  1991年   2篇
  1989年   1篇
  1985年   1篇
  1983年   1篇
  1982年   3篇
  1976年   1篇
  1975年   1篇
排序方式: 共有221条查询结果,搜索用时 15 毫秒
101.
Museum collections, species distributions, and rarefaction   总被引:3,自引:0,他引:3  
Biological specimens in museums and herbaria are sometimes used to compare the geographical distribution of different species. In doing so, it is necessary to account for differences in the numbers of specimens. We show how rarefaction can be used for this purpose. Rarefaction is a simple mathematical method originally designed to compare species richness in communities that differed in the number of sampled individuals. We present an example involving two Phragmipedium orchid species. In this case, rarefaction suggests that the apparent difference in range can be explained by the difference in the numbers of specimens.  相似文献   
102.
103.
Estimating species richness through extrapolation is becomingincreasingly important for conservation decision making. We present the resultsof a first test of four abundance-based estimation procedures, ACE, Chao1, Lognormal and Poisson lognormal based on single-sample museum collection data consisting of more than 150000specimens of 47 families of Danish Diptera. All four estimators considerablyunderestimate true species richness as assessed by species distributions, expertopinions, and a species–area curve. In our samples 3326 species wererepresented. The different estimators predicted the Danish fauna to consist of3490–3805 species, although at least 4361 are already known from theliterature. Expert opinion and the species–area curve indicate that theDanish fauna likely contains 5400–5800 species. The Poisson lognormalmethod displays a rather erratic behavior, but nonetheless performs slightlybetter than the other estimators. We discuss the inherent problems concerningthe use of collection data in this context as well as the influence of patchydistributions and sample size on estimator performance. We conclude thatabundance-based estimators should preferably be applied to almost completesamples of randomly distributed organisms.  相似文献   
104.
Population‐scale molecular studies of endangered and cryptic species are often limited by access to high‐quality samples. The use of noninvasively collected samples or museum‐preserved specimens reduces the pressure on modern populations by removing the need to capture and handle live animals. However, endogenous DNA content in such samples is low, making shotgun sequencing a financially prohibitive approach. Here, we apply a target enrichment method to retrieve mitochondrial genomes from 65 museum specimens and 56 noninvasively collected faecal samples of two endangered great ape species, Grauer's gorilla and the eastern chimpanzee. We show that the applied method is suitable for a wide range of sample types that differ in endogenous DNA content, increasing the proportion of target reads to over 300‐fold. By systematically evaluating biases introduced during target enrichment of pooled museum samples, we show that capture is less efficient for fragments shorter or longer than the baits, that the proportion of human contaminating reads increases postcapture although capture efficiency is lower for human compared to gorilla fragments with a gorilla‐generated bait, and that the rate of jumping PCR is considerable, but can be controlled for with a double‐barcoding approach. We succeed in capturing complete mitochondrial genomes from faecal samples, but observe reduced capture efficiency as sequence divergence increases between the bait and target species. As previously shown for museum specimens, we demonstrate here that mitochondrial genome capture from field‐collected faecal samples is a robust and reliable approach for population‐wide studies of nonmodel organisms.  相似文献   
105.
106.
黄宏文  廖景平 《生物多样性》2022,30(6):22220-468
植物园诞生的原初是“皇家”或“国家”意志的产物, 植物园的概念从公元前2,800年我国的“神农本草园”起源, 至今已历经沧桑巨变, 而西方文艺复兴后演替出了现代植物园。科研、保护、教育与示范四大功能始终是植物园的主线。植物园作为专门从事野生植物收集、科学研究、引种驯化和保护利用的专业研究机构, 始终肩负着国家的重要使命。本文系统综述了植物园的起源与演变, 并对世界各国的国家植物园与国家植物园体系进行了系统梳理和分析。在对我国植物园历史与发展概况总结的基础上, 论述了我国国家植物园体系建设的定位与目标、区域布局、科学研究、人才队伍、基础设施等五个方面的思考, 以任务带学科构建我国国家植物园迁地保护综合体系。  相似文献   
107.
根据已发表的麦族植物体Psy基因序列的保守区设计引物PsyO2,克隆小麦Psy基因(片段)。结果表明,PsyO2引物的扩增产物出现2种带型:196bp和233bp,序列分析表明两条特异条带涵盖了小麦Psy基因第2外显子全部序列,相差的37bp为Psy基因第2内含子中的一段插入序列,可反映不同黄色素含量(YPC),属小麦风,,基因的等位变异。验证试验表明,248份小麦微核心种质中有153份材料(占样品数的65.7%)扩增出196bp条带,群体内YPC均值7.314mg kg^-1,属高YPC范畴;另有95份材料(占样品总数的38.3%)扩增出233bp条带,群体内YPE均值为5.207mg kg^-1,属低YPC范畴,方差分析表明二者YPC差异达1%极显著水平差异,说明上述37bp的插入序列是导致小麦品种间YPC产生差异的原因之一,因此该引物扩增的Psy基因对小麦YPC具有显著影响,引物PsyO2是对小麦YPC进行分子鉴定的重要标记。  相似文献   
108.
Ongoing climate change affects various aspects of an animal's life, with important effects on distribution range and phenology. The relationship between global warming and body size changes in mammals and birds has been widely studied, with most findings indicating a decline in body size over time. Nevertheless, little data exist on similar size change patterns of invertebrates in general and insects in particular, and it is unclear whether insects should decrease in size or not with climate warming. We measured over 4000 beetle specimens, belonging to 29 beetle species in 8 families, collected in Israel during the last 100 years. The sampled species are all herbivorous. We examined whether beetle body size had changed over the years, while also investigating the relationships between body size and annual temperature, precipitation, net primary productivity (NPP) at the collection site and collection month. None of the environmental variables, including the collection year, was correlated with the size of most of the studied beetle species, while there were strong interactions of all variables with species. Our results, though mostly negative, suggest that the effect of climate change on insect body size is species‐specific and by no means a general macro‐ecological rule. They also suggest that the intrapopulation variance in body size of insects collected as adults in the field is large enough to conceal intersite environmental effects on body size, such as the effect of temperature and NPP.  相似文献   
109.
110.
David G. Furth 《ZooKeys》2013,(332):1-32
This is a preliminary study of the diversity of the Flea Beetles (Alticinae) of the Mexican state of Oaxaca based on fieldwork by the author in 1991, 1997, and 2010, the literature, and specimens in several institutional collections. The number of genera and species for Mexico as well as for Oaxaca increased significantly from previous studies. There are now 625 species in 90 genera recorded from Mexico with 275 species in 68 genera recorded from Oaxaca. There are 113 species known only from the state of Oaxaca and another 38 species known only from Oaxaca and the surrounding states. Oaxaca has a relatively high diversity as well as a high percentage of endemism. This study also demonstrates the effects of how even a small amount of fieldwork together with extracting specimen data from institutional collections can significantly increase the total faunistic and diversity knowledge of an area. A complete list of the genera and species known from Oaxaca is included.  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