全文获取类型
收费全文 | 179篇 |
免费 | 17篇 |
专业分类
林业 | 10篇 |
农学 | 5篇 |
基础科学 | 4篇 |
41篇 | |
综合类 | 15篇 |
农作物 | 6篇 |
水产渔业 | 31篇 |
畜牧兽医 | 65篇 |
园艺 | 8篇 |
植物保护 | 11篇 |
出版年
2023年 | 1篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 12篇 |
2016年 | 11篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 7篇 |
2012年 | 9篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 6篇 |
2008年 | 14篇 |
2007年 | 10篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 3篇 |
1995年 | 1篇 |
1993年 | 3篇 |
1972年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有196条查询结果,搜索用时 0 毫秒
41.
Conservation implications of establishment success of the Critically Endangered Twee River redfin ‘Pseudobarbus’ erubescens (Skelton, ) in an artificial impoundment in South Africa 下载免费PDF全文
Martine S. Jordaan Johannes A. van der Walt Zanné Brink Sonja Erasmus Olaf L. F. Weyl 《水产资源保护:海洋与淡水生态系统》2017,27(4):886-889
42.
Effect of an intensive mechanical removal effort on a population of non‐native rainbow trout Oncorhynchus mykiss in a South African headwater stream 下载免费PDF全文
Jeremy Shelton Olaf Weyl Johannes Van Der Walt Sean Marr Dean Impson Kristine Maciejewski Donovan Tye Helen Dallas Karen Esler 《水产资源保护:海洋与淡水生态系统》2017,27(5):1051-1055
43.
Olaf Anders 《Journal of pest science》1958,31(7):101-107
Ohne ZusammenfassungDie vorliegenden Untersuchungen wurden auf Anregung von Herrn Prof. Dr.-Ing. E. Schimitschek und mit Unterstützung der Landesforstverwaltungen Hessen und Schleswig-Holstein durchgeführt. 相似文献
44.
Sean C Anderson Andrew B Cooper Olaf P Jensen Cóilín Minto James T Thorson Jessica C Walsh Jamie Afflerbach Mark Dickey‐Collas Kristin M Kleisner Catherine Longo Giacomo Chato Osio Daniel Ovando Iago Mosqueira Andrew A Rosenberg Elizabeth R Selig 《Fish and Fisheries》2017,18(4):732-741
Fishery managers must often reconcile conflicting estimates of population status and trend. Superensemble models, commonly used in climate and weather forecasting, may provide an effective solution. This approach uses predictions from multiple models as covariates in an additional “superensemble” model fitted to known data. We evaluated the potential for ensemble averages and superensemble models (ensemble methods) to improve estimates of population status and trend for fisheries. We fit four widely applicable data‐limited models that estimate stock biomass relative to equilibrium biomass at maximum sustainable yield (B/BMSY). We combined these estimates of recent fishery status and trends in B/BMSY with four ensemble methods: an ensemble average and three superensembles (a linear model, a random forest and a boosted regression tree). We trained our superensembles on 5,760 simulated stocks and tested them with cross‐validation and against a global database of 249 stock assessments. Ensemble methods substantially improved estimates of population status and trend. Random forest and boosted regression trees performed the best at estimating population status: inaccuracy (median absolute proportional error) decreased from 0.42 – 0.56 to 0.32 – 0.33, rank‐order correlation between predicted and true status improved from 0.02 – 0.32 to 0.44 – 0.48 and bias (median proportional error) declined from ?0.22 – 0.31 to ?0.12 – 0.03. We found similar improvements when predicting trend and when applying the simulation‐trained superensembles to catch data for global fish stocks. Superensembles can optimally leverage multiple model predictions; however, they must be tested, formed from a diverse set of accurate models and built on a data set representative of the populations to which they are applied. 相似文献
45.
Aloisio C.D. Bueno Med Vet MS Barbara J. Watrous DVM Jill E. Parker VMD Olaf R. Hedstrom DVM Phd 《Veterinary radiology & ultrasound》2000,41(6):551-553
A 5-year-old Hereford cow was donated to Oregon State University, College of Veterinary Medicine. Two weeks before presentation the cow was treated by a left-flank laparotomy to correct a uterine torsion that revealed an excessive amount of abdominal fluid and a full term dead fetus. Ultrasonographic evaluation of the right cranioventral thoracic cavity was performed owing to physical examination (muffled heart sounds, areas of silence) and thoracocentesis findings suggestive of pleuritis. Ultrasonography revealed hypoechoic pleural effusion and a mass of mixed echogenicity visible within the right atrial lumen extending into the cranial vena cava. A diagnosis of cranial vena cava thrombosis was demonstrated at necropsy. The clinical, ultrasonographic, and pathological features of this less common condition (cranial vena cava thrombosis) in cattle are discussed. 相似文献
46.
Hanna Granroth-Wilding Craig Primmer Meri Lindqvist Jenni Poutanen Olaf Thalmann Jouni Aspi Jenni Harmoinen Ilpo Kojola Toni Laaksonen 《BMC ecology》2017,17(1):44
Background
Carnivores are re-establishing in many human-populated areas, where their presence is often contentious. Reaching consensus on management decisions is often hampered by a dispute over the size of the local carnivore population. Understanding the reproductive dynamics and individual movements of the carnivores can provide support for management decisions, but individual-level information can be difficult to obtain from elusive, wide-ranging species. Non-invasive genetic sampling can yield such information, but makes subsequent reconstruction of population history challenging due to incomplete population coverage and error-prone data. Here, we combine a collaborative, volunteer-based sampling scheme with Bayesian pedigree reconstruction to describe the pack dynamics of an establishing grey wolf (Canis lupus) population in south-west Finland, where wolf breeding was recorded in 2006 for the first time in over a century.Results
Using DNA extracted mainly from faeces collected since 2008, we identified 81 individual wolves and assigned credible full parentages to 70 of these and partial parentages to a further 9, revealing 7 breeding pairs. Individuals used a range of strategies to obtain breeding opportunities, including dispersal to established or new packs, long-distance migration and inheriting breeding roles. Gene flow occurred between all packs but inbreeding events were rare.Conclusions
These findings demonstrate that characterizing ongoing pack dynamics can provide detailed, locally-relevant insight into the ecology of contentious species such as the wolf. Involving various stakeholders in data collection makes these results more likely to be accepted as unbiased and hence reliable grounds for management decisions.47.
Cecilia M. Onyango Jeremy Harbinson Jasper K. Imungi Solomon S. Shibairo Olaf van Kooten 《Journal of plant nutrition》2013,36(3):342-365
The influence of manure and diammonium phosphate (DAP) mineral fertilizer on germination, leaf nitrogen content, nitrate accumulation and yield of vegetable amaranth (Amaranthus hypochondriacus) was investigated. Field trials were set up at the University of Nairobi Field Station at the Upper Kabete Campus during the long rains of March–May in 2007 and 2008. Trials were laid out as complete randomized block design with four fertilization treatments: 20, 40, and 60 kg nitrogen (N) ha?1 supplied by DAP (18:46:0), 40 kg N ha?1 supplied by cattle manure and an unfertilized control variant. The vegetables were harvested at three maturity stages at 6, 7, and 8 weeks after planting. Results indicated that there were significant differences between treatments in germination percentage, leaf nitrogen content, nitrate accumulation and vegetable yield. Plants that received manure had a higher germination percentage than those that received the same amount of N supplied by the chemical fertilizer DAP. The yields generally increased from week 6 to week 8. The highest yield was recorded in plots receiving 40 kg N ha?1 from DAP at eight weeks after planting. Plots that were supplied with manure recorded the lowest yield when compared to the fertilizer treated plots at all rates. Leaf nitrogen content increased with increasing rate of N but only when N was supplied by DAP fertilizer. The leaf nitrogen content decreased with increasing age of the plants. The leaf nitrate content increased with increase in DAP application rate. Results indicate that manure application produced quality vegetables in terms of low nitrate levels, but leaf nitrogen and vegetable yields were low. DAP application effected higher yields, but the vegetables had high though acceptable nitrate levels. 相似文献
48.
Gerd Wessolek Björn Kluge Steffen Trinks Michael Facklam Olaf Zeuschner 《Journal of Soils and Sediments》2018,18(2):481-493
Purpose
Wastewater irrigation is still a common practice in many cities worldwide. After ending the wastewater irrigation, the question arises as to how the highly polluted areas can be reused. Mostly, the remediation costs for liming or adding synthetic soil conditioners are too high for decision makers, often leading to unattractive wastelands in neighboring suburbs. This story shows how part of a former wastewater disposal field in Berlin (Germany) was remediated by adding and mixing loam-rich glacial until excavated from subway construction work. The remediation led to long-term improvements of soil and landscape, which nowadays is an attractive forested recreation area. Part of this landscape is used as an ecological lab for research, art, and education.Materials and methods
The article summarizes the results of soil analysis of the contamination status and remediation technique over the last 2 decades. We collected and reevaluated historical data, research results, technical reports, and graphic materials concerning the wastewater disposal field in Berlin, Germany.Results and discussion
The remediation concept without adding any synthetic substances was a successful soft technology leading to (i) a reduction of the long-term groundwater risk, (ii) an immobilization of the trace element concentration in the soil solution, and (iii) a reduction of the metal uptake by plants. Remediation led to much better conditions for plant growth, soil fauna, and microbiological activity, which improved the environment in a sustainable way. The implementation of a new landscape concept combining ecology, culture, and art totally changed the character of the landscape from former stinking wastewater fields to present-day attractive sites that can be used for many purposes.Conclusions
The remediation of the former wastewater disposal fields, using natural glacial till materials rich in clay and silt, became a “story of success.” However, a remediation project of this type and scope only becomes reality if all responsible actors in society participate continuously. We conclude that stakeholders should not focus only on remediation costs but also on the benefits for society: reclaiming waste sites significantly improves our well-being.49.
Olaf Butenschoen Christian Poll Ellen Kandeler Stefan Scheu 《Soil biology & biochemistry》2007,39(11):2854-2864
The effect of endogeic earthworms (Octolasion tyrtaeum (Savigny)) on the translocation of litter-derived carbon into the upper layer of a mineral soil by fungi was investigated in a microcosm experiment. Arable soil with and without O. tyrtaeum was incubated with 13C/15N-labelled rye leaves placed on plastic rings with gaze (64 μm mesh size) to avoid incorporation of leaves by earthworms. The plastic rings were positioned either on or 3 cm above the soil surface, to distinguish between biotic and chemical/physical translocation of nutrients by fungi and leaching.Contact of leaves to the soil increased 13C translocation, whereas presence of O. tyrtaeum reduced the incorporation of 13C into the mineral soil in all treatments. Although biomass of O. tyrtaeum decreased during the experiment, more 13C and 15N was incorporated into earthworm tissue in treatments with contact of leaves to the soil. Contact of leaves to the soil and the presence of O. tyrtaeum increased cumulative 13CO2-C production by 18.2% and 14.1%, respectively.The concentration of the fungal bio-indicator ergosterol in the soil tended to be increased and that of the fungal-specific phospholipid fatty acid 18:2ω6 was significantly increased in treatments with contact of leaves to the soil. Earthworms reduced the concentration of ergosterol and 18:2ω6 in the soil by 14.0% and 43.2%, respectively. Total bacterial PLFAs in soil were also reduced in presence of O. tyrtaeum, but did not respond to the addition of the rye leaves. In addition, the bacterial community in treatments with O. tyrtaeum differed from that without earthworms and shifted towards an increased dominance of Gram-negative bacteria.The results indicate that litter-decomposing fungi translocate litter-derived carbon via their mycelial network in to the upper mineral soil. Endogeic earthworms decrease fungal biomass by grazing and disruption of fungal hyphae thereby counteracting the fungal-mediated translocation of carbon in soils. 相似文献
50.
David Persson Hvard Bjrgen Alexander Figenschou Linn‐Anett Hillestad Erling Olaf Koppang Ane Ndtvedt Marit Stormoen 《Journal of fish diseases》2021,44(1):25-32
Fish gills are heavily exposed to the external milieu and may react against irritants with different cellular responses. We describe variations in mucous cell counts in gills from healthy Atlantic salmon (Salmo salar) presmolts in five recirculating aquaculture system (RAS) farms and one flow‐through farm. Based on certain criteria, mucous cells were histologically quantified in a defined lamellar region of the gills and the counts were analysed. Immunohistochemistry (IHC) was used to investigate epithelial responses. The median number of total mucous cells in the defined region was 59 per fish. Between the farms, the medians varied from 31 to 101 with the lowest in the flow‐through farm. A regression model was fitted with “total mucous cells” as the dependent variable and with “fish length” and “fish farm” as independent variables. The proportion of variation in mucous cell counts explained by the model was twice as high when “fish farm” was included compared to only “fish length.” IHC revealed proliferative responses in coherence with high mucous cell numbers. Conclusively, the variation in mucous cell counts depends on combined farm‐related factors. Establishing a baseline for mucous cell counts is fundamental in the development of high‐throughput monitoring programmes of gill health in farmed fish. 相似文献