全文获取类型
收费全文 | 2313篇 |
免费 | 200篇 |
国内免费 | 109篇 |
出版年
2024年 | 5篇 |
2023年 | 59篇 |
2022年 | 60篇 |
2021年 | 111篇 |
2020年 | 114篇 |
2019年 | 106篇 |
2018年 | 118篇 |
2017年 | 76篇 |
2016年 | 78篇 |
2015年 | 82篇 |
2014年 | 202篇 |
2013年 | 245篇 |
2012年 | 175篇 |
2011年 | 128篇 |
2010年 | 82篇 |
2009年 | 107篇 |
2008年 | 146篇 |
2007年 | 122篇 |
2006年 | 92篇 |
2005年 | 90篇 |
2004年 | 64篇 |
2003年 | 52篇 |
2002年 | 37篇 |
2001年 | 30篇 |
2000年 | 27篇 |
1999年 | 25篇 |
1998年 | 17篇 |
1997年 | 19篇 |
1996年 | 15篇 |
1995年 | 14篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 34篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有2622条查询结果,搜索用时 15 毫秒
51.
52.
Elizabeth A. DiGangi Jonathan D. Bethard 《American journal of physical anthropology》2021,175(2):422-436
Since the professionalization of US-based forensic anthropology in the 1970s, ancestry estimation has been included as a standard part of the biological profile, because practitioners have assumed it necessary to achieve identifications in medicolegal contexts. Simultaneously, forensic anthropologists have not fully considered the racist context of the criminal justice system in the United States related to the treatment of Black, Indigenous, and People of Color; nor have we considered that ancestry estimation might actually hinder identification efforts because of entrenched racial biases. Despite ongoing criticisms from mainstream biological anthropology that ancestry estimation perpetuates race science, forensic anthropologists have continued the practice. Recent years have seen the prolific development of retooled typological approaches with 21st century statistical prowess to include methods for estimating ancestry from cranial morphoscopic traits, despite no evidence that these traits reflect microevolutionary processes or are suitable genetic proxies for population structure; and such approaches have failed to critically evaluate the societal consequences for perpetuating the biological race concept. Around the country, these methods are enculturated in every aspect of the discipline ranging from university classrooms, to the board-certification examination marking the culmination of training, to standard operating procedures adopted by forensic anthropology laboratories. Here, we use critical race theory to interrogate the approaches utilized to estimate ancestry to include a critique of the continued use of morphoscopic traits, and we assert that the practice of ancestry estimation contributes to white supremacy. Based on the lack of scientific support that these traits reflect evolutionary history, and the inability to disentangle skeletal-based ancestry estimates from supporting the biological validity of race, we urge all forensic anthropologists to abolish the practice of ancestry estimation. 相似文献
53.
54.
Carlos Bustamante Ana M. García-Cegarra Carolina Vargas-Caro 《Journal of fish biology》2021,98(3):870-873
The presence of four sharks was documented in coastal waters of Antofagasta (Chile) using an unmanned aerial video camera. Fishers took advantage of this aggregation to catch and sold three adult broadnose sevengill sharks Notorynchus cepedianus. Species identity was determined by using the cox1 gene. One additional video was later recorded 3000 km south of Antofagasta, and shows a large female interacting with a salmon farming facility. Shallow water records of N. cepedianus were previously undocumented in Chilean waters, yet historically have provided an opportunistic event to fishers in Chile. 相似文献
55.
Natasha D. Phillips Amy Garbett Daniel Wise Sophie L. Loca Olivia Daly Lawrence E. Eagling Jonathan D. R. Houghton Peter Verhoog James Thorburn Patrick C. Collins 《Journal of fish biology》2021,99(4):1492-1496
Essential fish habitats (EFHs) are critical for fish life-history events, including spawning, breeding, feeding or growth. This study provides evidence of EFHs for the critically endangered flapper skate (Dipturus intermedius) in the waters around the Orkney Isles, Scotland, based on citizen-science observation data. The habitats of potential egg-laying sites were parametrised as >20 m depth, with boulders or exposed bedrock, in moderate current flow (0.3–2.8 knots) with low sedimentation. This information provides a significant contribution to the understanding of EFHs for flapper skate. 相似文献
56.
大尺度陆地生态系统动态变化与空间变异的过程模型及模拟系统 总被引:1,自引:0,他引:1
当代生态系统科学研究更加关注区域生态环境及生态系统状态变化的监测、评估、预测、预警及生态环境可持续管理。在深入理解陆地生态系统的要素、过程、功能、格局及其相互作用机理基础上,发展生态系统定量化描述方法和数值模拟技术,集成构建大陆尺度的“多过程耦合-多技术集成-多目标应用”的陆地生态系统数值模拟器已成为生态系统与全球变化及其资源、环境和灾害效应科学研究的重要科技任务。本研究围绕宏观生态系统模拟分析方法问题,在回顾陆地生态系统模型研究现状和发展趋势的基础上,深入讨论开发大尺度陆地生态系统动态变化和空间变异及其资源环境效应模拟系统的理念,以及模拟系统的功能定位、结构设计等基本问题,为构造中国陆地生态系统数值模拟器提供参考。 相似文献
57.
Mohamed G. Nasser Eslam M. Hosni Mohamed A. Kenawy Sulaiman A. Alharbi Hesham S. Almoallim Magda H. Rady Bouthaina A. Merdan Adrian C. Pont Sara A. Al-Ashaal 《Saudi Journal of Biological Sciences》2021,28(4):2056-2066
The family Calliphoridae is a group of heterogenous calyptrate flies with a worldwide distribution including species of ecological, veterinary, medical, and forensic importance. Notorious for their parasitic habits, the larvae of many blowflies are characterised – like some other dipteran larvae – by their ability to develop in animal flesh. When parasitism affects a living host, it is termed “myiasis”. This has led the Calliphoridae to be considered as a pivotal family in its relationship with a man. Nevertheless, even after more than 50 years of research, the phylogenetic relationships among calliphorid subfamilies together with the evolutionary origin of myiasis remain unclear. In order to elucidate these problems, we constructed three phylogenetic trees by using nucleotide sequence data from cytochrome oxidase subunit one (COI), representing a mitochondrial conservative gene, and nuclear 28S subunit of ribosomal RNA gene (28S rRNA) in order to interpret the evolutionary profile of myiasis in the family Calliphoridae. The sequenced data represented species associated with ectoparasitic life-styles, either saprophagy or facultative and obligate parasitism. A total number of 50 accessions were collected for 28S rRNA, 56 for COI, and 38 for combined sequences phylogeny. Molecular Evolutionary Genetics Analysis (MEGA) software was used to align 2197 nucleotide positions of 28S rRNA and 1500 nucleotide positions of COI with a gap opening penalties and gap extension penalties equalling 20 and 0.1 respectively. The results reveal the non-monophyly of the family Calliphoridae despite the stable monophyletic status of the Chrysomyinae, Luciliinae, and Auchmeromyiinae. Also, our findings recommend ranking the Toxotarsinae as a separate family. Furthermore, comparative analysis of the phylogenetic trees shows that the habit of obligatory myiasis originated independently more than five times. This strengthens our hypothesis that the origin of eating fresh meat is a case of convergent evolution that has taken place after speciation events millions of years ago. Finally, estimating the divergence dates between lineages from molecular sequences provides a better chance of understanding their evolutionary biology. 相似文献
58.
Elizabeth A. Sinclair Craig D. H. Sherman John Statton Craig Copeland Andrew Matthews Michelle Waycott Kor‐Jent van Dijk Adriana Vergs Lana Kajlich Ian M. McLeod Gary A. Kendrick 《Ecological Management & Restoration》2021,22(1):10-21
Three case studies involving two temperate Australian seagrass species – Pondweed (Ruppia tuberosa) and Ribbon Weed (Posidonia australis) – highlight different approaches to their restoration. Seeds and rhizomes were used in three collaborative programmes to promote new approaches to scale up restoration outcomes. 相似文献
59.
CRISPR/Cas9是新兴的基因编辑技术,在生命科学研究中发挥着重要的作用。将它引入本科生的实验教学,使本科生了解这项前沿科研技术很有意义。我们创建了一个基于CRISPR/ Cas9技术的本科教学实验体系。该实验体系侧重CRISPR/Cas9技术在哺乳动物细胞中的应用,选用一株基因组上被插入mCherry基因的小鼠胚胎成纤维细胞为实验材料,命名为STO-82。首先设计靶向mCherry的sgRNA,构建CRISPR-Cas9/sgRNA共表达质粒。经测序验证无误后,转染到STO-82细胞。采用流式细胞仪分析检测mCherry阴性和阳性两群细胞,分选出阴性单细胞并扩大培养。最后用测序检验单克隆细胞中靶标DNA序列的编辑情况。结果显示,靶位点有插入或缺失突变,说明体系创建成功。该实验体系将sgRNA设计、CRISPR-Cas9/sgRNA共表达质粒的构建、细胞转染、单细胞分选、单克隆细胞培养、测序序列分析等内容融合为一个综合实验,用于高年级本科生的实验教学。根据实际情况,将教学实践内容分解分块教学,也可以做完整性项目教学。本教学实践采用10人左右的小班分块教学,2人一组,经过3个班(共13组)的实践,绝大部分学生都能完成实验,得到预期结果。通过这个实验,学生加深了对CRISPR/Cas9技术的原理和实验流程的理解,锻炼了实验操作能力和严谨的科研思维,也使学生对该技术的医疗应用风险有了一些认识。 相似文献
60.
Paul H. Gobster Ingrid E. Schneider Kristin M. Floress Anna L. Haines Arne Arnberger Michael J. Dockry Claire Benton 《Restoration Ecology》2021,29(1)
Pine barrens are open‐canopy ecological communities once prevalent on sandy soils across the northern Great Lakes Region of the United States and Canada, though fire suppression and plantation forestry have now reduced them to a few isolated areas. Efforts to restore pine barrens are underway on some public lands, but lack of knowledge on the social and ecological issues and challenges that affect these projects impedes fuller progress. As a precursor to designing a public preference survey for pine barrens restoration, we sought input from those with expert knowledge about pine barrens. Using a three‐round modified Delphi survey, forest land managers and researchers identified the key characteristics of pine barrens and important current and future management challenges. Key characteristics were related to fire, landscape structure, plant and animal species, soils, and social themes. Current and future challenges were related to landscape, invasive species, social, economic, climate change, and science themes. Four social issues (education, fire acceptance, fire risk, aesthetics) were rated among the top current challenges but none of them maintained prominence as future challenges. Potential explanations for this shift are that the experts felt these social concerns would be resolved in time or that other issues, such as development pressures and budgets for carrying out restoration, would become greater future challenges. Our approach can be used by managers and researchers to better understand the ecosystems they seek to restore and to communicate with public stakeholders about restoration efforts. 相似文献