全文获取类型
收费全文 | 5943篇 |
免费 | 630篇 |
国内免费 | 536篇 |
专业分类
7109篇 |
出版年
2024年 | 28篇 |
2023年 | 249篇 |
2022年 | 189篇 |
2021年 | 269篇 |
2020年 | 291篇 |
2019年 | 372篇 |
2018年 | 292篇 |
2017年 | 286篇 |
2016年 | 270篇 |
2015年 | 258篇 |
2014年 | 317篇 |
2013年 | 406篇 |
2012年 | 281篇 |
2011年 | 249篇 |
2010年 | 201篇 |
2009年 | 261篇 |
2008年 | 267篇 |
2007年 | 298篇 |
2006年 | 250篇 |
2005年 | 234篇 |
2004年 | 214篇 |
2003年 | 196篇 |
2002年 | 180篇 |
2001年 | 149篇 |
2000年 | 141篇 |
1999年 | 111篇 |
1998年 | 73篇 |
1997年 | 68篇 |
1996年 | 47篇 |
1995年 | 49篇 |
1994年 | 51篇 |
1993年 | 48篇 |
1992年 | 47篇 |
1991年 | 44篇 |
1990年 | 31篇 |
1989年 | 26篇 |
1988年 | 40篇 |
1987年 | 54篇 |
1986年 | 22篇 |
1985年 | 32篇 |
1984年 | 20篇 |
1983年 | 33篇 |
1982年 | 26篇 |
1981年 | 29篇 |
1980年 | 24篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1974年 | 8篇 |
排序方式: 共有7109条查询结果,搜索用时 15 毫秒
991.
992.
基于表型数据的辣椒核心种质构建研究 总被引:1,自引:0,他引:1
以收集保存的603份辣椒种质为材料,根据果形指数大小将其分成5组。基于28个性状的表型数据,采用简单比例、平方根比例、对数比例及遗传多样性指数比例法计算各组内取样份数,比较4种组内取样比例法、6种总体取样规模和2种取样方法在构建辣椒核心种质中的作用和效果。结果表明:(1)简单比例、平方根比例、对数比例、遗传多样性指数比例法入选的材料份数占预选核心种质份数依次为24.2%、22.2%、21.1%、17.8%,说明遗传多样性指数比例法对各组取样数量的修正能力最强,使取样更加均衡。(2)当总体取样规模为15%时,遗传多样性指数比例法构建的预选核心种质遗传多样性指数(I)达到最大,表型保留比例(RPR)超过98%;当总体取样规模超过20%时,RPR值、变异系数(CV)和极差符合率(CR)虽然平缓增加,但I值反而减小;说明15%为合适的总体取样规模。(3)利用对数比例法和多样性比例法,在15%的总体取样规模下,聚类取样构建的核心种质I值、RPR值、CV值及CR值均高于随机取样。(4)该研究根据所获得的优化方案最终在表型水平建立了包含91份种质的辣椒核心种质。 相似文献
993.
994.
Building strong relationships between conservation genetics and primary industry leads to mutually beneficial genomic advances 下载免费PDF全文
Stephanie J. Galla Thomas R. Buckley Rob Elshire Marie L. Hale Michael Knapp John McCallum Roger Moraga Anna W. Santure Phillip Wilcox Tammy E. Steeves 《Molecular ecology》2016,25(21):5267-5281
Several reviews in the past decade have heralded the benefits of embracing high‐throughput sequencing technologies to inform conservation policy and the management of threatened species, but few have offered practical advice on how to expedite the transition from conservation genetics to conservation genomics. Here, we argue that an effective and efficient way to navigate this transition is to capitalize on emerging synergies between conservation genetics and primary industry (e.g., agriculture, fisheries, forestry and horticulture). Here, we demonstrate how building strong relationships between conservation geneticists and primary industry scientists is leading to mutually‐beneficial outcomes for both disciplines. Based on our collective experience as collaborative New Zealand‐based scientists, we also provide insight for forging these cross‐sector relationships. 相似文献
995.
北京地区油松潜在重要害虫松阴吉丁的形态和生物学特性观察 总被引:2,自引:0,他引:2
【目的】调查松阴吉丁Phaenops yin KubáňBíly(鞘翅目:几丁甲科)对北京地区油松Pinus tabuliformis Carrière的危害情况,了解该害虫的生物学特性;分析其偶然性暴发成灾的原因及规律,探讨该害虫的综合治理措施。【方法】本研究通过林间采集、解剖受害木段以及实验室罩笼饲养等方法,调查了松阴吉丁的发生现状,包括油松的受害情况和受害症状、天敌生物等,并结合历史文献和北京地区近20年的气象资料分析了该虫偶然暴发的原因。【结果】松树死亡率约为30%,受害株率约为60%,发现两种主要寄生性天敌始刻柄茧蜂Atanycolus initiator(Fabricius)和赤腹深沟茧蜂Iphiaulax impostor(Scopoli)。【结论】该虫在我国北方地区偶然性暴发的主要原因可能与持续高温干旱和降雨量减少导致的油松长势衰弱有关。建议结合气象变化及时预测预报松阴吉丁的发生,通过补水降温、清理枯枝、保护天敌、合理用药等综合治理措施调控该害虫的种群动态。 相似文献
996.
Stefan Pauliuk Guillaume Majeau‐Bettez Daniel B. Müller Edgar G. Hertwich 《Journal of Industrial Ecology》2016,20(6):1260-1272
The complexity of data and methods in industrial ecology (IE) keeps growing, and the demand for comprehensive and interdisciplinary assessments increases. To keep up with this development, the field needs a data infrastructure that allows researchers to annotate, store, retrieve, combine, and exchange data at low cost, without loss of information, and across disciplines and model frameworks. A consensus‐building debate about how to describe the common object of study, socioeconomic metabolism (SEM), is necessary for the development of practical data structures and databases. We review the definitions of basic concepts to describe SEM in IE and related fields such as integrated assessment modeling. We find that many definitions are not compatible, are implicit, and are sometimes lacking. To resolve the conflicts and inconsistencies within the current definitions, we propose a hierarchical system of terms and definitions, a practical ontology, for describing objects, their properties, and events in SEM. We propose a typology of object properties and use sets to group objects into a hierarchical, mutually exclusive, and collectively exhaustive (H‐MECE) classification. This grouping leads to a general definition of stocks. We show that a MECE representation of events necessarily requires two complementary concepts: processes and flows, for which we propose general definitions based on sets. Using these definitions, we show that the system structure of any interdisciplinary model of SEM can be formulated as a directed graph. We propose guidelines for semantic data annotation and database design, which can help to turn the vision of a powerful data infrastructure for SEM research into reality. 相似文献
997.
Eric W.M. Stienen Peter Desmet Bart Aelterman Wouter Courtens Simon Feys Nicolas Vanermen Hilbran Verstraete Marc Van de Walle Klaas Deneudt Francisco Hernandez Robin Houthoofdt Bart Vanhoorne Willem Bouten Roland-Jan Buijs Marwa M. Kavelaars Wendt Müller David Herman Hans Matheve Alejandro Sotillo Luc Lens 《ZooKeys》2016,(555):115-124
In this data paper, Bird tracking - GPS tracking of Lesser Black-backed Gulls and Herring Gulls breeding at the southern North Sea coast is described, a species occurrence dataset published by the Research Institute for Nature and Forest (INBO). The dataset (version 5.5) contains close to 2.5 million occurrences, recorded by 101 GPS trackers mounted on 75 Lesser Black-backed Gulls and 26 Herring Gulls breeding at the Belgian and Dutch coast. The trackers were developed by the University of Amsterdam Bird Tracking System (UvA-BiTS, http://www.uva-bits.nl). These automatically record and transmit bird movements, which allows us and others to study their habitat use and migration behaviour in great detail. Our bird tracking network is operational since 2013. It is funded for LifeWatch by the Hercules Foundation and maintained in collaboration with UvA-BiTS and the Flanders Marine Institute (VLIZ). The recorded data are periodically released in bulk as open data (http://dataset.inbo.be/bird-tracking-gull-occurrences), and are also accessible through CartoDB and the Global Biodiversity Information Facility (GBIF). 相似文献
998.
S. Martellos 《Plant biosystems》2016,150(4):616-621
Primary biodiversity data are often organised in federated databases in the framework of big international projects and initiatives. Other data are normally organised into isolated resources: ecological, morphological and morpho-anatomic databases, checklists, archives of digital identification tools, etc. These data, which do not refer specifically to one specimen or observation, but to a taxon, can be addressed to as “taxon-related data”. In the framework of the Italian Biodiversity Network, taxon-related data have been aggregated by using a federated approach, with the creation of a network of data providers, which required the development of a communication protocol, the species-related data (SRD) protocol and of a simple data format (the SRD format). The SRD federated database aggregates currently ca. 70,000 taxon pages for several groups of organisms: vascular plants, lichens, mosses, algae, freshwater fishes and butterflies. All these resources can be queried by using one simple interface in the web portal of the Italian Biodiversity Network (http://www.naturaitalia.it/nnb/). 相似文献
999.
The effectiveness and credibility of environmental decisions depend on the information provided by scientific assessments. However, the conflicting assessments provided by government agencies, industries, and environmental advocacy groups suggest that biases occur during assessment processes. Sources of bias include personal bias, regulatory capture, advocacy, reliance on volunteer assessors, biased stakeholder and peer review processes, literature searches, standardization of data, inappropriate standards of proof, misinterpretation, and ambiguity. Assessors can adopt practices to increase objectivity, transparency, and clarity. Decision-makers, managers of assessors, and institutions that commission assessments can adopt other practices that reduce pressures on assessors and reduce opportunities for expression of the personal biases of assessors. Environmental assessment should be recognized as a discipline with its own technical and ethical best practices. 相似文献
1000.
George E. Halkos Nickolaos G. Tzeremes Stavros A. Kourtzidis 《Journal of Industrial Ecology》2016,20(5):1159-1175
In this article, we apply an additive two‐stage data envelopment analysis estimator on a panel of 20 countries with advanced economies for the time period 1990–2011 in order to create a composite sustainability efficiency index. We use a window‐based approach in order to study the countries over the years. The sustainability efficiency index is decomposed into production efficiency and eco‐efficiency indicators. The results reveal inequalities among the examined countries between the two stages. The eco‐efficiency stage is characterized by large inequalities among countries and significantly lower efficiency scores than the overall sustainability efficiency and the production efficiency. Finally, it is reported that a country's high production efficiency level does not ensure a high eco‐efficiency performance. 相似文献