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   1055篇
  免费   101篇
  国内免费   70篇
  2024年   3篇
  2023年   21篇
  2022年   33篇
  2021年   52篇
  2020年   28篇
  2019年   46篇
  2018年   38篇
  2017年   36篇
  2016年   33篇
  2015年   25篇
  2014年   79篇
  2013年   95篇
  2012年   67篇
  2011年   43篇
  2010年   34篇
  2009年   45篇
  2008年   50篇
  2007年   50篇
  2006年   60篇
  2005年   75篇
  2004年   65篇
  2003年   34篇
  2002年   42篇
  2001年   30篇
  2000年   27篇
  1999年   16篇
  1998年   20篇
  1997年   15篇
  1996年   10篇
  1995年   11篇
  1994年   15篇
  1993年   12篇
  1992年   6篇
  1991年   2篇
  1990年   3篇
  1989年   2篇
  1988年   1篇
  1985年   1篇
  1974年   1篇
排序方式: 共有1226条查询结果,搜索用时 15 毫秒
991.
Aim To improve our understanding of species range limits by studying how height growth, a trait related to plant survival, varies throughout the geographic range of Fagus sylvatica L. in France. Location The geographic range of beech in France, representing the western area of its European distribution, within which this species exhibits range distribution limits in both plains and mountainous areas. Methods A generalized linear regression model was used to link beech growth performance to environmental variables using data from 819 plots of the French National Forest Inventory (IFN) database. This model was applied to predict potential growth on 97,281 IFN plots covering the geographic range of beech in France. A kriging technique was used to interpolate estimated growth potential. Finally, the performance of plot‐based predictions of potential growth from the map (i.e. map quality) was evaluated against an independent data set. Results The beech growth performance model highlighted the major impact of climate on potential tree growth at a broad spatial scale. The relevant climatic factors were related mainly to spring cold, summer heat, and winter temperatures and rainfall. The study also revealed the predictive power of soil parameters, which explained a large proportion of the variation in potential beech growth (c. 30%). Analyses of height growth patterns near the boundary of the species range in France showed that the limit only partly coincides with the growth decline caused by climatic and soil factors. Along parts of the range limit, the predicted potential for growth was high, suggesting that in these areas the limit of the range could be explained by other factors, such as competition or constraints on reproduction. Main conclusions The spatial variation in the potential height growth of Fagus sylvatica can be explained by environmental factors and is partly correlated with its regional range limits. By identifying areas where growth potential constrains the geographic range of species, environmental growth models can help to improve our knowledge of the spatial drivers of species geographic range limits and shed light on their response to future environmental changes.  相似文献   
992.
海洋生物多样性甚高, 但却饱受人为的破坏及干扰。目前全球最大的含点位数据的在线开放性数据库是海洋生物地理信息系统(OBIS), 共约12万种3,700万笔资料; 另一个较大的数据库世界海洋生物物种登录(WoRMS)已收集全球22万种海洋生物之物种分类信息。除此之外, 以海洋生物为主的单一类群的数据库只有鱼库(FishBase)、藻库(AlgaeBase)及世界六放珊瑚(Hexacorallians of the World)3个。跨类群及跨陆海域的全球性物种数据库则甚多, 如网络生命大百科(EOL)、全球生物物种名录(CoL)、整合分类信息系统(ITIS)、维基物种(Wikispecies)、ETI生物信息(ETI Bioinformatics)、生命条形码(BOL)、基因库(GenBank)、生物多样性历史文献图书馆(BHL)、海洋生物库(SeaLifeBase); 海洋物种鉴定入口网(Marine Species Identification Portal)、FAO渔业及水产养殖概要(FAO Fisheries and Aquaculture Fact Sheets)等可查询以分类或物种解说为主的数据库。全球生物多样性信息网络(GBIF)、发现生命(Discover Life)、水生物图库(AquaMaps)等则是以生态分布数据为主, 且可作地理分布图并提供下载功能, 甚至于可以改变水温、盐度等环境因子的参数值, 利用既定的模式作参数改变后之物种分布预测。谷歌地球(Google Earth)及国家地理(National Geographic)网站中的海洋子网页, 以及珊瑚礁库(ReefBase)等官方机构或非政府组织之网站, 则大多以海洋保育的教育倡导为主, 所提供的信息及素材可谓包罗万象, 令人目不暇给。更令用户感到方便的是上述许多网站或数据库彼此间均已可交互链接及查询。另外, 属于搜索引擎的谷歌图片(Google Images)与谷歌学术(Google Scholar)透过海洋生物数据库所提供的直接链接, 在充实物种生态图片与学术论文上亦发挥极大帮助, 让用户获得丰富多样的信息。为了保育之目的, 生物多样性数据库除了整合与公开分享外, 还应鼓励并推荐大家来使用。本文乃举Rainer Froese在巴黎演讲之内容为例, 介绍如何使用海洋生物多样性之数据来预测气候变迁对鱼类分布的影响。最后就中国大陆与台湾目前海洋生物多样性数据库的现况、两岸的合作及如何与国际接轨作介绍。  相似文献   
993.
Proteomic analysis of bovine conceptus fluid proteins during early pregnancy has the potential to expose protein species indicative of both the overall health of the fetal-maternal environment and fetal developmental status. In this study, we examined the differential abundance of bovine conceptus fluid proteins (5-50 kDa fraction) from naturally conceived, in vitro fertilisation (IVF) and somatic cell nuclear transfer (SCNT)-derived pregnancies at days 45 and 90 of gestation. In day 45 allantoic fluid (AllF) samples, an atypical cluster of low molecular weight ( approximately 14-16 kDa), low pI (between 3.0 and 4.5 pH units) protein species was increased in three of four IVF samples (30-100-fold increase in protein spot volumes compared to normal). These proteins were identified as paralogs of the bovine cathelicidin antimicrobial protein (CAMP) by MALDI-TOF MS peptide mass fingerprint and MALDI-TOF MS/MS peptide sequence analysis. Peptidoglycan recognition protein and serine (or cysteine) proteinase inhibitor clade B1, were also significantly increased in the corresponding IVF samples. In two of four SCNT AllF samples, a 2-10-fold increase in CAMP protein spot volumes were detected. No aberrant abundance levels of individual protein species were observed in amniotic fluid samples, or in day 90 IVF AllF samples. Identification of unique protein species present in the normal bovine AllF proteome at day 45 is also reported.  相似文献   
994.
Metabolism of halophilic archaea   总被引:1,自引:0,他引:1  
In spite of their common hypersaline environment, halophilic archaea are surprisingly different in their nutritional demands and metabolic pathways. The metabolic diversity of halophilic archaea was investigated at the genomic level through systematic metabolic reconstruction and comparative analysis of four completely sequenced species: Halobacterium salinarum, Haloarcula marismortui, Haloquadratum walsbyi, and the haloalkaliphile Natronomonas pharaonis. The comparative study reveals different sets of enzyme genes amongst halophilic archaea, e.g. in glycerol degradation, pentose metabolism, and folate synthesis. The carefully assessed metabolic data represent a reliable resource for future system biology approaches as it also links to current experimental data on (halo)archaea from the literature. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   
995.
The present study is a report of data of planktonic dinoflagellates which includes a list of 252 species, with 10 985 entries in the southern Gulf of Mexico along with information concerning their occurrence. Material for the present study consists of water and net samples obtained during 11 cruises collected at 608 sites between June 1979 and December 2002. Ceratium (47 spp.), Protoperidinium (28 spp.), Dinophysis (26 spp.), Oxytoxum (19 spp.) and Prorocentrum (15 spp.) were the most diverse genera. The most common species found are Ceratium breve, Ceratium contortum, Ceratium furca, Ceratium furca var. eugranum, Ceratium fusus. Ceratium fusus var. seta, Ceratium kofoidii, Ceratium macroceros, Ceratium massiliense, Ceratium pentagonum, Ceratium teres, Ceratium trichoceros, Ceratium tripos, Dinophysis caudata, Ornithocercus magnificus, Podolampas palmipes, Prorocentrum com‐pressum, Prorocentrum gracile, Prorocentrum micans, Protoperidinium divergens and Pyrophacus steinii. Thirteen species are potential toxin producers, among which Karenia brevis was responsible for fish mass mortalities. Other toxic species such as Amphidinium carterae, Dinophysis acuta, Dinophysis caudata, Dinophysis fortii, Dinophysis mitra, Dinophysis rotundata, Dinophysis tripos, Prorocentrum mexicanum, Prorocentrum micans and Prorocentrum minimum were present mostly in net samples. The non‐toxic species Ceratium furca, Pyrodinium bahamense var. bahamense, Scripp‐siella trochoidea and Gonyaulax polygram ma were found in blooms during the summer. Qualitative data show that dinoflagellates occurred mostly during July and August, associated with hydrographic conditions. A checklist of the species and their occurrence are given.  相似文献   
996.
随着后基因组时代的到来,非编码区的研究已经成为科学家面临的挑战,对基因非编码区的一个主要研究方向就是对调控元件的研究。识别转录调控元件是理解基因转录机制和表达模式的关键。较全面地介绍了基因非编码区以及调控元件,包括功能和作用,常用识别算法,并对常用数据库进行介绍,提出可能的研究方法和发展方向。  相似文献   
997.
Mitochondria are crucial for normal cell metabolism and maintenance. Mitochondrial dysfunction has been implicated in a spectrum of human diseases, ranging from rare monogenic to common multifactorial disorders. Important for the understanding of organelle function is the assignment of its constituents, and although over 1,500 proteins are predicted to be involved in mammalian mitochondrial function, so far only about 900 are assigned to mitochondria with reasonable certainty. Continuing efforts are being taken to obtain a complete inventory of the mitochondrial proteome by single protein studies and high-throughput approaches. To be of best value for the scientific community this data needs to be structured, explored, and customized. For this purpose, the MitoP2 database () was established and is maintained in order to incorporate such data. The central database contains manually evaluated yeast, mouse, and human reference proteins, which show convincing evidence of a mitochondrial location. In addition, entries from genome-wide approaches that suggest protein localization are integrated and serve to compile a combined score for each candidate, which provides a best estimate of mitochondrial localization. Furthermore, it integrates information on the orthology between species, including Saccharomyces cerevisiae, mouse, human, Arabidopsis thaliana, and Neurospora crassa, thus mutually enhancing evidence across species. In contrast to other known databases, MitoP2 takes into account the reliability by which the protein is estimated as being mitochondrially located, as described herein. Multiple search functions, as well as information on disease causing genes and available mouse models, makes MitoP2 a valuable tool for the genetic investigation of human mitochondrial pathology.  相似文献   
998.
Genome downsizing in polyploid plants   总被引:18,自引:0,他引:18  
All else being equal, polyploids are expected to have larger C-values (amount of DNA in the unreplicated gametic nucleus) than their diploid progenitors, increasing in direct proportion with ploidy. This expectation is observed in some polyploid series, especially those newly formed, but there are examples suggesting that C-values in particular polyploids are less than expected. The availability of the Angiosperm DNA C-values database ( http://www.rbgkew.org.uk/cval/homepage.html ) has allowed this question to be addressed across a broad range of angiosperms and has revealed striking results deviating from expectation: (i) mean 1C DNA amount did not increase in direct proportion with ploidy, and (ii) mean DNA amount per basic genome (calculated by dividing the 2C value by ploidy) tended to decrease with increasing ploidy. These results suggest that loss of DNA following polyploid formation, or genome downsizing, may be a widespread phenomenon of considerable biological significance. Recent advances in our understanding of the molecular events that take place following polyploid formation together with new data on how DNA amounts can both increase and decrease provide some insights into how genome downsizing may take place. The nature of the evolutionary forces that may be driving DNA loss are also discussed.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 651–663.  相似文献   
999.
庄永龙  周敏  李衍达  沈岩 《遗传》2004,26(4):514-518
随着人类基因组序列草图的完成,基因组突变的研究显得日益重要,而越来越多的突变信息的积累,使得各种突变数据库相继诞生。本文根据各种数据库的功能,对目前的人类突变相关数据库资源进行了分类总结,分类为突变数据库、单核苷酸多态信息数据库、与疾病相关的突变数据库、突变对蛋白质的影响、突变图谱以及特定基因的突变信息,分析该如何合理使用这些遗传突变数据资源,以及目前的突变数据库所存在的问题。Abstract:Researches on genome mutation are becoming more and more important with the finish of human genome DNA draft. This review is to classify the existing human mutation databases, including mutation database, SNP(single nucleotide polymorphisms) databases, mutation databases about disease, mutation databases about proteins, mutation databases about map and mutation information about specific gene. We also give advice on how to utilize these mutation databases, and discuss problems of existing databases.  相似文献   
1000.
The KEGG pathway maps are widely used as a reference data set for inferring high-level functions of the organism or the ecosystem from its genome or metagenome sequence data. The KEGG modules, which are tighter functional units often corresponding to subpathways in the KEGG pathway maps, are designed for better automation of genome interpretation. Each KEGG module is represented by a simple Boolean expression of KEGG Orthology (KO) identifiers (K numbers), enabling automatic evaluation of the completeness of genes in the genome. Here we focus on metabolic functions and introduce reaction modules for improving annotation and signature modules for inferring metabolic capacity. We also describe how genome annotation is performed in KEGG using the manually created KO database and the computationally generated SSDB database. The resulting KEGG GENES database with KO (K number) annotation is a reference sequence database to be compared for automated annotation and interpretation of newly determined genomes.  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