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   946篇
  免费   51篇
  国内免费   1篇
林业   29篇
农学   17篇
基础科学   6篇
  93篇
综合类   164篇
农作物   31篇
水产渔业   31篇
畜牧兽医   570篇
园艺   17篇
植物保护   40篇
  2021年   8篇
  2020年   9篇
  2019年   9篇
  2018年   19篇
  2017年   10篇
  2016年   20篇
  2015年   19篇
  2014年   23篇
  2013年   72篇
  2012年   23篇
  2011年   34篇
  2010年   20篇
  2009年   36篇
  2008年   28篇
  2007年   44篇
  2006年   29篇
  2005年   25篇
  2004年   28篇
  2003年   30篇
  2002年   21篇
  2001年   28篇
  2000年   16篇
  1999年   20篇
  1998年   19篇
  1997年   13篇
  1996年   11篇
  1993年   8篇
  1992年   21篇
  1991年   26篇
  1990年   18篇
  1989年   20篇
  1988年   14篇
  1987年   9篇
  1986年   20篇
  1985年   15篇
  1984年   13篇
  1983年   10篇
  1982年   7篇
  1979年   18篇
  1978年   10篇
  1976年   14篇
  1975年   7篇
  1974年   15篇
  1973年   10篇
  1972年   10篇
  1970年   9篇
  1969年   9篇
  1968年   7篇
  1967年   13篇
  1966年   9篇
排序方式: 共有998条查询结果,搜索用时 0 毫秒
151.
Organics found in comet 81P/Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some organics are similar, but not identical, to those in interplanetary dust particles and carbonaceous meteorites. A class of aromatic-poor organic material is also present. The organics are rich in oxygen and nitrogen compared with meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than are meteorites and interplanetary dust particles. The presence of deuterium and nitrogen-15 excesses suggest that some organics have an interstellar/protostellar heritage. Although the variable extent of modification of these materials by impact capture is not yet fully constrained, a diverse suite of organic compounds is present and identifiable within the returned samples.  相似文献   
152.
Trimethylamine oxide (TMAO) is found at high levels in wild Atlantic cod. Trimethylamine oxide is reduced to trimethylamine (TMA) during iced storage. In this study, the levels of TMAO and TMA in wild and farmed cod and the impact of storage, gender and season on these levels were investigated. Wild cod had higher levels of TMAO than farmed cod. Wild cod also had higher levels of TMA after 15 days of iced storage. Farmed cod were found to have levels of TMA‐N <5 mg/100 g after 15 days of iced storage, which is below the maximum permitted level for fresh fish. Therefore, TMA appears to be an unsuitable measure of freshness in farmed cod. Female farmed cod had higher levels of TMAO than male farmed cod; no such difference between genders was found in wild cod. Female and male farmed cod had similar levels of TMA after post‐mortem iced storage. The hepatosomatic index (HSI) of female farmed cod was higher than that seen in male cod and this may be the underlying reason for the differences in muscle TMAO. Levels of TMAO in male farmed cod were higher during the autumn and were correlated with a larger HSI during the same period.  相似文献   
153.
This paper investigates the ethical values, moral principles, methods and reform proposals in aquaculture ethics scholarship to develop a comprehensive and balanced list of aquaculture ethical principles. A Systematic Quantitative Literature Review methodology is employed to parse 150 journal articles on aquaculture ethics. Methodologies, specific ethical values, broad principles, recommended reforms and trends over time are quantified and assessed. Through analysis of invoked values and recommended reforms, six core marine economy ethics principles are identified: Environmental Protection, Fairness, Stakeholder Participation, Harm Prevention, Beneficence and Trustworthiness. A comprehensive multidimensional legitimacy model is employed to uncover ethical gaps and identify promising areas for future aquaculture ethics research.  相似文献   
154.
155.
156.
157.
158.
Data from post-mortem and field studies were obtained that discussed poisoning in ostriches following ingestion of toxic plants. From the notes, all plants studied caused death in ostriches and there was systemic organ damage. Poisoning from Sarcostemma viminale (Melktou) resulted in beak patting, muscular tremors and head flopping, followed by collapse and violent kicking before death. Ingestion of Combretum oatesii (Red wings) seeds from plants in free grazing pastures resulted in vomiting, restlessness, eyelid flicking, collapse and kicking movements. Dichapetalum cymosum (Gifblaar) killed an ostrich after episodes of shaking legs, rapid respiration and bradycardia and hyperaemia of the lungs, liver and kidneys. Poisoning from Senecio sceleratus (Ragwort) caused skin haemorrhages and bleeding in tracheal mucous membranes, the pericardium, diaphragm and interperitoneal membrane. Consumption of drupes from Melia azedarach (Syringa berry) caused muscle tremors, kicking movements and respiratory distress. Lantana camara (Cherry pie) poisoning resulted in extremely inflamed eyes with copious yellow exudates extending down their beaks and onto their necks. Bentonite was administered by gavage at a dose of 5 g/kg. Poisoning in these cases is usually associated with the farmer allowing his/her birds to roam free-range in paddocks in which toxic plants are growing. Toxic plants should be removed from grass cut for hay. The author is willing to send photographs of all poisonous plants if requested by a reader.  相似文献   
159.
The diets suitable for the hand rearing of piglets in incubators were examined. Diet A was based on cows' milk heated to 56 degrees C and had bacteriostatic and antiadhesive properties against Escherichia coli. Diet B was based on evaporated cows' milk and did not have these properties. The numbers of coliform bacteria naturally colonising the small intestines of newborn piglets fed entirely on these diets for one week did not differ significantly, however both were significantly higher than in control piglets suckled from birth. Faecal counts of coliforms were similar in all three groups. Examination of the bacteriostatic sensitivity of the isolated strains to sows' milk indicated a predominance of milk-sensitive strains colonising the suckled piglets and a predominance of milk-resistant strains in the piglets fed diet B. This diet-dependent colonisation could not be explained by the in vitro bacteriostatic properties of the diets alone.  相似文献   
160.
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