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   96篇
  免费   4篇
林业   11篇
农学   1篇
基础科学   1篇
  14篇
综合类   13篇
农作物   12篇
水产渔业   7篇
畜牧兽医   27篇
园艺   6篇
植物保护   8篇
  2023年   2篇
  2022年   3篇
  2021年   5篇
  2020年   5篇
  2019年   3篇
  2018年   3篇
  2017年   2篇
  2016年   1篇
  2015年   1篇
  2014年   8篇
  2013年   4篇
  2012年   6篇
  2011年   8篇
  2010年   5篇
  2009年   3篇
  2008年   4篇
  2007年   7篇
  2006年   2篇
  2005年   10篇
  2004年   2篇
  2003年   2篇
  2002年   2篇
  2001年   1篇
  1995年   1篇
  1994年   2篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1980年   2篇
  1976年   2篇
排序方式: 共有100条查询结果,搜索用时 62 毫秒
71.
European eel, Anguilla anguilla L., migrating to the sea encounter many man‐made structures that can hamper and delay migration or induce mortality. Studying small‐scale behavioural movements in front of these man‐made structures could provide insight in further mitigating adverse effects. The behaviour of eel approaching a trash rack in front of a large pumping station was investigated using a dual‐frequency identification sonar (DIDSON). Eels approaching the trash rack swam through the rack (40.5%) but also showed turning behaviour at (44.7%) or in front of the rack (14.7%). Eels approaching the rack had varying body positions, predominantly head or tail first, but also curled up into a ball or drifted sideways. After turning in front or at the trash rack, eels showed upstream and downwards swimming towards the canal bottom. The results suggest a stepwise response to potential cues, when firstly the body position is changed in such a way that secondly, later on, enhances eventual fast upstream escapement when perceived necessary. Implications for management of these behavioural observations are discussed.  相似文献   
72.
Offshore activities elevate ambient sound levels at sea, which may affect marine fauna. We reviewed the literature about impact of airgun acoustic exposure on fish in terms of damage, disturbance and detection and explored the nature of impact assessment at population level. We provided a conceptual framework for how to address this interdisciplinary challenge, and we listed potential tools for investigation. We focused on limitations in data currently available, and we stressed the potential benefits from cross‐species comparisons. Well‐replicated and controlled studies do not exist for hearing thresholds and dose–response curves for airgun acoustic exposure. We especially lack insight into behavioural changes for free‐ranging fish to actual seismic surveys and on lasting effects of behavioural changes in terms of time and energy budgets, missed feeding or mating opportunities, decreased performance in predator‐prey interactions, and chronic stress effects on growth, development and reproduction. We also lack insight into whether any of these effects could have population‐level consequences. General “population consequences of acoustic disturbance” (PCAD) models have been developed for marine mammals, but there has been little progress so far in other taxa. The acoustic world of fishes is quite different from human perception and imagination as fish perceive particle motion and sound pressure. Progress is therefore also required in understanding the nature and extent to which fishes extract acoustic information from their environment. We addressed the challenges and opportunities for upscaling individual impact to the population, community and ecosystem level and provided a guide to critical gaps in our knowledge.  相似文献   
73.
Studies on chronic or acute toxicity of nitrogen species on fish in recirculating aquaculture systems (RAS) usually focused on adverse effects of total ammonia nitrogen (TAN: sum of NH3 + NH4+) and nitrite (), while underestimating the potential effects of high nitrate accumulation on growth and health status of fish. In our study, Nile tilapia (Oreochromis niloticus) were exposed to five different nitrate concentrations (0, 10, 100, 500 and 1000 mg L?1 ‐N) over 30 days. Growth parameters (feed conversion ratio (FCR), specific growth rate (SGR), hepatosomatic index (HSI)), blood samples (concentrations of haemoglobin, methaemoglobin, plasma /) and the histology of the gills were studied to evaluate growth and health status of the fish. At the highest nitrate concentration, the fish showed significantly reduced growth and impaired health status (SGR, FCR, plasma /, haemoglobin and methaemoglobin concentration), demonstrating that too high nitrate concentrations can negatively influence tilapia production in RAS. Here, we recommend not exceeding concentrations of 500 mg L?1 ‐N in juvenile tilapia culture to ensure an optimal health and growth status of the fish, as below that concentration no effects on the tilapia have been observed.  相似文献   
74.
Hemibastadin derivatives, including the synthetically-derived 5,5′-dibromohemibastadin-1 (DBHB), are potent inhibitors of blue mussel phenoloxidase (PO), which is a key enzyme involved in the firm attachment of this invertebrate to substrates and, thus, a promising molecular target for anti-fouling research. For a systematic investigation of the enzyme inhibitory activity of hemibastadin derivatives, we have synthesized nine new congeners, which feature structural variations of the DBHB core structure. These structural modifications include, e.g., different halogen substituents present at the aromatic rings, different amine moieties linked to the (E)-2-(hydroxyimino)-3-(4-hydroxyphenyl)propionic acid, the presence of free vs. substituted aromatic hydroxyl groups and a free vs. methylated oxime group. All compounds were tested for their inhibitory activity towards the target enzyme in vitro, and IC50 values were calculated. Derivatives, which structurally closely resemble sponge-derived hemibastadins, revealed superior enzyme inhibitory properties vs. congeners featuring structural moieties that are absent in the respective natural products. This study suggests that natural selection has yielded structurally-optimized antifouling compounds.  相似文献   
75.
A cat with an upper respiratory infection was presented for examination. Close examination of the face revealed a firm, haired rounded swelling on the bridge of the nose. Serum protein electrophoresis demonstrated a mild hypergammaglobulinaemia. The cat tested negative for feline immunodeficiency virus. Skin biopsy of the nasal lesion revealed nodular angiocentric infiltrates in the deep dermis and subcutis. The mixed infiltrate had numerous plasma cells. Presence of calicivirus antigen could not be demonstrated within the skin lesion by immunohistochemical staining. The cat was treated for upper respiratory infection and 1 month later the nasal lesion had resolved. A firm and rounded swelling over the bridge of the nose may be a feline cutaneous plasmacytic reaction pattern.  相似文献   
76.
 马铃薯晚疫病广谱抗性基因Rpi-blb1(克隆于Solanum bulbocastanum)及其两个同源抗病基因Rpi-sto1(克隆于Solanum stoloniferum)和Rpi-pta1(克隆于Solanum papita)的抗性可能已被高度进化的晚疫病菌株所克服。为证实此观点,将从荷兰田间和墨西哥野外S. bulbocastanum 和S. stoloniferum 病株上采集的晚疫病菌株重新接种于具有共同遗传背景(感病栽培品种Desiree)的Rpi-blb1 及其同源基因转化体和3个野生种植株上,测试Rpi-blb1 及其同源基因的抗性是否已被克服。结果表明,采自墨西哥野外S. stoloniferum的两个菌株Pic99189 和Pic99192 已经克服了Rpi-blb1 及其同源基因的抗性;在野生种植株的测试中,只有S. papita 的抗性明显地被菌株Pic99192 所克服。同时发现在转基因植株离体叶片接种试验中,高抗晚疫病菌的转化体需要在多个转化体间进行选择。从采自中国4 个不同地区晚疫病菌株接种sto1.Desiree 转化体的小规模测试中可推断,Rpi-blb1 及其同源抗性基因在中国仍具有潜在的应用价值。  相似文献   
77.
78.
79.
Trees of the family Dipterocarpaceae are the dominant trees in Southeast Asian tropical forests where they play an important ecological role and are also important commercially. An experiment was conducted to determine the effect of ectomycorrhizal fungi on the growth of dipterocarp species in peat soils. Seedlings of Shorea pinanga were inoculated with spores of two ectomycorrhizal fungi, Pisolithus arhizus and Scleroderma sp. were grown in pots containing sterilized peat soil for 7 months. The percentage of ectomycorrhizal colonization on S. pinanga exceeded 86%. Colonization of S. pinanga roots by ectomycorrhizal fungi resulted in increased shoot height, stem diameter, number of leaves, and shoot fresh and dry weight. Survival rates of S. pinanga were greater for inoculated seedlings than control seedlings. These results suggest that inoculation of ectomycorrhizal fungi can improve the early growth of S. pinanga grown in tropical forests and that this technique will accelerate the rehabilitation of degraded dipterocarp forests.  相似文献   
80.
Five novel DNA-dependent DNA polymerase (Dpol) herpesviral sequences were generated using nested consensus polymerase chain reaction (PCR) in clinical samples from a harbor seal (Phoca vitulina), bottlenose dolphin (Tursiops truncatus), orca (Orcinus orca), California sea lion (Zalophus californianus), and a Phocid herpesvirus 2 (PhHV-2) isolate from a harbor seal (used as positive control). These novel sequences and other representative herpesvirus sequences were included in Bayesian and Maximum Likelihood analyses to illustrate the phylogeny of herpesviruses amongst the marine mammal host species and in comparison to those of other animals. All 19 novel and known marine mammal herpesviruses included in the analyses aligned with members of the Alphaherpesvirinae or Gammaherpesvirinae subfamilies. The novel harbor seal herpesvirus clustered with members of the Macavirus genus, subfamily Gammaherpesvirinae. The novel bottlenose dolphin herpesvirus clustered together in a monophyletic group with another delphinid alphaherpesvirus but could not be associated with an established genus. The orca herpesvirus also clustered with a delphinid alphaherpesvirus and formed a separate clade. The sea lion herpesvirus clustered with PhHV-2. PhHV-1 clustered with varicelloviruses and PhHV-2 clustered strongly in the Gammaherpesvirinae genus Percavirus. All cetacean gammaherpesviruses formed a monophyletic clade and could not be associated with an established gammaherpesviral genus.  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