全文获取类型
收费全文 | 955篇 |
免费 | 67篇 |
国内免费 | 4篇 |
专业分类
林业 | 102篇 |
农学 | 27篇 |
基础科学 | 6篇 |
211篇 | |
综合类 | 111篇 |
农作物 | 37篇 |
水产渔业 | 137篇 |
畜牧兽医 | 301篇 |
园艺 | 17篇 |
植物保护 | 77篇 |
出版年
2023年 | 9篇 |
2022年 | 7篇 |
2021年 | 21篇 |
2020年 | 27篇 |
2019年 | 24篇 |
2018年 | 30篇 |
2017年 | 22篇 |
2016年 | 43篇 |
2015年 | 32篇 |
2014年 | 44篇 |
2013年 | 54篇 |
2012年 | 59篇 |
2011年 | 74篇 |
2010年 | 53篇 |
2009年 | 39篇 |
2008年 | 63篇 |
2007年 | 76篇 |
2006年 | 65篇 |
2005年 | 55篇 |
2004年 | 41篇 |
2003年 | 34篇 |
2002年 | 38篇 |
2001年 | 20篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 10篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1971年 | 4篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1956年 | 4篇 |
排序方式: 共有1026条查询结果,搜索用时 20 毫秒
1.
Ahmed Faraj Ali Al-Zankana Lisa S. Smallwood Tom Matheson David M. Harper 《水产资源保护:海洋与淡水生态系统》2021,31(10):2697-2713
- Many river rehabilitation projects have been criticized for failing to meet their goals or for being insufficiently monitored. There is, therefore, an urgent need to develop robust approaches for assessing treatment efficacy and thus guide the increasing investment in rehabilitation.
- Instream biotopes (formerly called ‘functional habitats’ or ‘mesohabitats’ by different authors) and their macroinvertebrate assemblages were used to assess the effectiveness of entire-channel hydromorphological rehabilitation of a 1.8-km stretch of a lowland stream through the town of Market Harborough, Leicestershire, UK.
- The project successfully enhanced the physical diversity, measured in the rehabilitated reach as the coefficients of variability for channel water depth and width, wet surface area, number of instream biotopes, and biotope diversity.
- The project also enhanced the biodiversity conservation value, measured as macroinvertebrate total density, total biomass, richness, diversity, Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness, EPT diversity, EPT count%, and EPT biomass%, all of which significantly increased following rehabilitation. Chironomidae count% and biomass% significantly decreased following rehabilitation. Rehabilitation was also successful in significantly increasing macroinvertebrate shredder, scraper, and filter-feeder group density.
- Changes in the macroinvertebrate community metrics in the rehabilitated reach were related significantly to changes in the percentages of cover of instream biotopes and increases in biotope diversity in the rehabilitated reach.
- Macroinvertebrate structural and functional metrics can provide quantitative data for assessing reach-level rehabilitation outcomes, if samples are collected in a pre-defined sampling protocol stratified at the instream biotope level.
- The practical implications of this work are that the design of rehabilitation projects, if based upon the recreation of biotope heterogeneity, will succeed in improving biological value and restoring the area to near naturalness if a suitable upstream source of macroinvertebrates for natural recolonization is available. The study shows that the concept of biotopes has an important role to play in river conservation management.
2.
3.
Shah Mujahid Ali Saito Taiju Šindelka Radek Iegorova Viktoriia Rodina Marek Baloch Abdul Rasheed Franěk Roman Tichopád Tomáš Pšenička Martin 《Fisheries Science》2021,87(1):71-83
Fisheries Science - The cleavage pattern of a vertebrate’s embryo is either holoblastic (complete) or meroblastic (partial). Sturgeon and other basal bony fishes represent a transition of the... 相似文献
4.
Wheat stem rust, caused by the fungus Puccinia graminis f. sp. tritici (Pgt), is a notoriously damaging disease of wheat and barley. Pgt requires two hosts to complete its lifecycle; undergoing asexual reproduction on cereal crops and completing sexual reproduction on Berberis spp. The latter stage of its lifecycle is of particular importance in temperate regions such as western Europe, where asexual urediniospores are unable to survive cold winter weather. In the past, the crucial role of Berberis in the lifecycle of stem rust led to intensive eradication campaigns, initially carried out by farmers in the face of hostile scientific opinion. In the United Kingdom, common barberry (Berberis vulgaris) is today a relatively rare plant. Stem rust is, however, currently experiencing a resurgence; at the same time, there has been a general increase in the prevalence of barberry and an upsurge in its planting which, in the United Kingdom, is associated with attempts to encourage the endangered barberry carpet moth (Pareulype berberata). This article situates current developments within a broader chronological framework, examining changing attitudes towards barberry and rust in England in the past and the history of the plant's use and cultivation. It assesses how widespread B. vulgaris really was in the environment historically, and thus the scale of its eradication. We suggest that Berberis was never widely established as an archaeophyte in the United Kingdom. Current attempts to re-establish it are based on a misunderstanding of the plant's historical status and could potentially pose a serious threat to food security. 相似文献
5.
Movement behaviour of large female yellow European eel (Anguilla anguilla L.) in a freshwater polder area 下载免费PDF全文
Pieterjan Verhelst Jan Reubens Ine Pauwels David Buysse Bart Aelterman Stijn Van Hoey Peter Goethals Tom Moens Johan Coeck Ans Mouton 《Ecology of Freshwater Fish》2018,27(1):471-480
Due to a recruitment decline of more than 90% in 30 years, the European eel (Anguilla anguilla L.) has been classified by IUCN as critically endangered. Although the species has been studied intensively to obtain knowledge to improve management, studies about the resident yellow stage are relatively scarce. In this study, 52 large female yellow eels were tagged with acoustic transmitters in a Belgian polder system and tracked by a network of 23 automatic listening stations. We studied both circadian and seasonal movement patterns and the effect of environmental variables on these patterns. Large female yellow eels were most active at night in late summer and early autumn. A generalised linear mixed model showed that their movement is only slightly influenced by environmental variables. Moreover, as yellow eels show high site fidelity (i.e., the majority was detected only in the habitat type of their catch‐release location), they do not encounter many human‐induced connectivity problems in polder systems, which makes these systems highly suitable as eel growth habitat. These results can contribute to an effective eel management regarding habitat protection and restoration. 相似文献
6.
Stable isotopes and gut contents indicate differential resource use by coexisting asp (Leuciscus aspius) and pikeperch (Sander lucioperca) 下载免费PDF全文
Mojmír Vašek Antti P. Eloranta Ivana Vejříková Petr Blabolil Milan Říha Tomáš Jůza Marek Šmejkal Josef Matěna Jan Kubečka Jiří Peterka 《Ecology of Freshwater Fish》2018,27(4):1054-1065
Differential use of habitat and prey resources is an important mechanism that may allow coexistence of sympatric species. Unlike interactions between smaller cyprinid and percid fishes, the resource use by coexisting predatory asp (Leuciscus aspius) and pikeperch (Sander lucioperca) is relatively unknown. Here, gut content and stable isotope analyses were used to study ontogenetic dietary shifts and interspecific trophic niche overlap between asp and pikeperch coexisting in two reservoirs. The hypothesis that both species show an ontogenetic dietary shift from small invertebrates to large fish prey, but at the same time use different prey resources to reduce potential competitive interactions, was validated. The isotopic niches of the two predators showed no, or only a moderate, degree of overlap (0%–65%). The ontogenetic changes in the degree of interspecific isotopic niche overlap were different in the two reservoirs, suggesting that trophic segregation can be dynamic and variable among systems. Gut contents revealed that small (<100 mm standard length) asp consumed mostly terrestrial invertebrates and emerged aquatic insects, whereas small pikeperch foraged on zooplankton, larval and pupal stages of aquatic insects and fish. Larger individuals (>100 mm) of both species were predominantly piscivorous, with asp consuming more cyprinid prey and pikeperch more percid prey. Coexisting asp and pikeperch populations are able to utilise different prey resources, thereby reducing potential negative competitive interactions. 相似文献
7.
Influence of orthopedic reinforced gloves versus double standard gloves on contamination events during small animal orthopedic surgery 下载免费PDF全文
8.
正棉籽酸脱绒会危害育种家人身安全和潜在环境。需要1种无需用酸,能有效去除棉短绒且对棉种萌发无不利影响的脱绒方法。为了优化棉籽机械脱绒流程,美国农业部农业研究中心(USDA-ARS)棉花生产与加工部门(Lubbock,Texas)研发创制了一台棉籽机械脱绒样机(图1,图2)。测试设计了应用7种滚筒衬垫(1种是不用任何研磨材料,其余6种分别采用不同的研磨材料)、1个或2个辊刷"擦 相似文献
9.
Otolith elemental characteristics of whitefish (Coregonus lavaretus) from brackish waters of the Gulf of Bothnia,Baltic Sea 下载免费PDF全文
Henry Hägerstrand Mikael Himberg Erkki Jokikokko Mikael von Numers Lucyna Mrówczyńska Anti Vasemägi Tom Wiklund Jan‐Olof Lill 《Ecology of Freshwater Fish》2017,26(1):66-74
To investigate whether European whitefish (Coregonus lavaretus) groups in the brackish (≤7%) Gulf of Bothnia (Baltic Sea) express specific otolith elemental characteristics, concentrations of elements (Ca, Ba, Sr, Zn, Mn, Fe) in whole otoliths were studied by inductively coupled plasma‐optical emission spectrometry. Whitefish (N = 67) were sampled from six different latitudinal sites; four in the sea and two in rivers along the west coast of Finland, and from a fresh water lake for comparison. The concentration of several elements showed significant differences among sampling sites. Otolith Ba concentrations were higher at the northern sampling sites compared to the southern ones, thereby showing negative association to capture‐habitat salinity. In contrast, otolith Sr and Zn concentrations were lower at the northern sampling sites, thereby associating positively to capture‐habitat salinity. Otolith Mn concentrations did not associate with latitude or salinity but markedly varied between sampling sites. Elevated Fe concentrations occurred in fish otoliths from the two northernmost sites. Ca concentrations were at the same levels in otoliths from all whitefish samples. Otoliths of whitefish from the lake had very high Ba and low Sr concentrations compared to concentrations in otoliths from whitefish in the sea and rivers. Our results show that otolith elemental characteristics of whitefish vary considerably at various geographic scales showing high potential for population identification using elemental fingerprints. Analysis of otolith elemental characteristics may therefore provide an efficient tool for the identification of main areas of residence, spawning locations, and migration routes, thus contributing towards the sustainable management of whitefish stocks. 相似文献
10.
The impact of truncating data on the predictive ability for single‐step genomic best linear unbiased prediction 下载免费PDF全文
Jeremy T. Howard Tom A. Rathje Caitlyn E. Bruns Danielle F. Wilson‐Wells Stephen D. Kachman Matthew L. Spangler 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2018,135(4):251-262
Simulated and swine industry data sets were utilized to assess the impact of removing older data on the predictive ability of selection candidate estimated breeding values (EBV) when using single‐step genomic best linear unbiased prediction (ssGBLUP). Simulated data included thirty replicates designed to mimic the structure of swine data sets. For the simulated data, varying amounts of data were truncated based on the number of ancestral generations back from the selection candidates. The swine data sets consisted of phenotypic and genotypic records for three traits across two breeds on animals born from 2003 to 2017. Phenotypes and genotypes were iteratively removed 1 year at a time based on the year an animal was born. For the swine data sets, correlations between corrected phenotypes (Cp) and EBV were used to evaluate the predictive ability on young animals born in 2016–2017. In the simulated data set, keeping data two generations back or greater resulted in no statistical difference (p‐value > 0.05) in the reduction in the true breeding value at generation 15 compared to utilizing all available data. Across swine data sets, removing phenotypes from animals born prior to 2011 resulted in a negligible or a slight numerical increase in the correlation between Cp and EBV. Truncating data is a method to alleviate computational issues without negatively impacting the predictive ability of selection candidate EBV. 相似文献