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   531篇
  免费   35篇
  国内免费   2篇
林业   15篇
农学   16篇
基础科学   5篇
  64篇
综合类   117篇
农作物   34篇
水产渔业   23篇
畜牧兽医   265篇
园艺   4篇
植物保护   25篇
  2023年   5篇
  2020年   7篇
  2019年   7篇
  2018年   9篇
  2017年   16篇
  2016年   10篇
  2015年   5篇
  2014年   12篇
  2013年   19篇
  2012年   11篇
  2011年   21篇
  2010年   11篇
  2009年   19篇
  2008年   24篇
  2007年   20篇
  2006年   19篇
  2005年   12篇
  2004年   20篇
  2003年   19篇
  2002年   12篇
  2001年   11篇
  2000年   9篇
  1999年   11篇
  1998年   7篇
  1997年   12篇
  1996年   7篇
  1995年   8篇
  1994年   5篇
  1993年   6篇
  1992年   13篇
  1991年   8篇
  1990年   7篇
  1989年   13篇
  1988年   6篇
  1987年   7篇
  1986年   8篇
  1985年   9篇
  1984年   8篇
  1982年   5篇
  1980年   5篇
  1978年   6篇
  1977年   4篇
  1976年   5篇
  1975年   8篇
  1974年   5篇
  1973年   9篇
  1972年   5篇
  1970年   4篇
  1969年   5篇
  1968年   4篇
排序方式: 共有568条查询结果,搜索用时 31 毫秒
1.
Prevalence of Cryptosporidium sp in equids in Louisiana   总被引:3,自引:0,他引:3  
In 1985, 22 pony foals reared in a helminth-free environment were tested daily for oocysts of Cryptosporidium sp by use of fecal flotation. Oocysts were found in all foals. Oocysts were first observed in feces collected from foals 9 to 28 days after birth. The mean period of oocyst shedding was 10 days and ranged from 2 to 18 days in individual foals. Diarrhea was observed in 14 of 22 (64%) foals and began before the period of oocyst shedding. Fecal samples also were examined for other infective agents. Salmonella poona was isolated from 1 foal that did not have diarrhea, and coronavirus particles were observed in the feces of 2 foals with diarrhea. Cryptosporidium sp oocysts also were observed in feces of 2 of 17 Thoroughbred foals, 3 of 14 Quarter Horse foals, and 3 of 26 pony foals reared on pastures with their dams. Samples from pasture-reared foals were collected at irregular intervals. Of the 11 Cryptosporidium-positive fecal samples collected from pastured foals, 2 were from foals with diarrhea. A similar survey was conducted during the 1986 foaling season, using the same procedures. Examination of 300 samples from 58 Quarter Horse, Arabian, and pony foals did not detect oocysts. Daily examination of feces from 10 pony foals reared under helminth-free conditions for 30 days also failed to detect Cryptosporidium oocysts.  相似文献   
2.
SUMMARY An aqueous suspension of air-dried, hammer-milled leaf of Terminalla oblongata (yellow-wood) was administered to sheep by gavage, as a single dose of 5 to 20 g (dry weight)/kg body weight. Doses of 15 g/kg, or more, caused depression, Inappetence, abdominal pain and reduced ruminal movements within 24 to 48 h and some sheep also showed dyspnoea, oplsthotonus and champing of the Jaws. Haematology and blood gas and acid-base measurements were unaffected. In sheep given a dose of 12.5 g/kg, or more, plasma osmolality, aspartate aminotransferase activity and potassium and bilirubin concentrations Increased while plasma total protein markedly decreased and plasma sodium concentration and alkaline phosphatase activity remained normal. Most sheep were necropsled 48 h after dosing. The liver showed zonal hepatocellular necrosis, the pattern of which varied with the dose given. No renal lesions were observed, although one sheep given a very high dose became azotaemic and hyperkalaemic. Hydrothorax, hydroperlcardlum and ascltes developed In sheep given doses of 15 or 20 g/kg.  相似文献   
3.
4.
5.
The existing standardised test systems for assessing the toxicity of crop protection products to the non-target arthropods Typhlodromus pyri (Acari: Phytoseiidae) and Aphidius rhopalosiphi (Hymenoptera: Aphidiidae) are limit tests designed to compare a single-use rate of the product with a water control. The suitability of these test systems for generating dose-response data as required for refined ecotoxicological risk assessment was evaluated. Data on dose-response toxicity of crop protection products to T. pyri and A. rhopalosiphi were generated under worst-case laboratory and to T. pyri under extended laboratory conditions and analysed using the standard Probit method, a logistic regression, a generalised Probit analysis, and the moving average-angle method in order to calculate the LR50-values (application rate killing 50% of the exposed organisms). The fit of the models, the precision of the resulting LR50 values, and the required minimum number of replicates were compared. In 85% of the studies, at least one of the statistical methods led to satisfactory results. The moving average-angle method was the most widely applicable method. The results show that the existing guidelines can be used to perform dose-response tests. Implications for risk assessment are discussed.  相似文献   
6.
7.
8.
Extrapulmonary granulomatous lesions associated with a naturally acquired Paragonimus kellicotti infection were observed in a dog with severe pulmonary paragonimiasis. Lung lesions were similar to those previously described. Extrapulmonary granulomatous lesions were found in the liver, mediastinal lymph nodes, spermatic cord and the tunica vaginalis. Extravascular deposition of eggs in the spermatic cord and tunica vaginalis caused a perilymphatic granulomatous inflammation and partially occlusive lymphangitis with dilatation of the external lymphatic vessel of the right spermatic cord.  相似文献   
9.
Birds can reduce production of shrimp in mariculture grow-out ponds through predation and competition for feed. This study involved weekly nocturnal enumeration of bird populations and observation of nocturnal avian habits on a series of 0.1 ha experimental ponds at the Texas A&M University Shrimp Mariculture Facility at Corpus Christi, Texas. Observations were conducted hourly from sunset to sunrise during October through December 1980. The rate of predation was evaluated every three hours by comparing the number of feeding attempts to the number of successful prey captures over a known time period. Gulls (Family Laridae) acted primarily as competitors for feed. Active feeding by gulls was restricted to daylight hours, consequently feed loss decreased when the feed was distributed at or after dusk. Major preadatory birds included herons and egrets (F. Ardeidae), migratory ducks (F. Anatidae), and, to a lesser extent, grebes (F. Podicipedidae) and shorebirds (Order Charadriiformes). Bird predation decreased pond production by 75% in some ponds.  相似文献   
10.
In 1910, H. B. Fantham described the life cycle of a coccidian parasite in birds. Fantham was a parasitologist at Cambridge University in the United Kingdom working for an enquiry into diseases affecting the red grouse. Despite the growing importance of the poultry industry and the realization that coccidiosis was an important disease of the fowl, little further work was carried out in the United Kingdom until coccidiosis research was initiated at the Veterinary Laboratory, Weybridge almost 30 yr later. Further progress depended upon research carried out at academic and agricultural institutions in the United States. E. E. Tyzzer at Harvard University provided the solid foundation upon which our present knowledge of coccidiosis, and the species of Eimeria involved in the disease, is based. Agricultural experiment stations (AESs) throughout the nation played an important role in communicating advances to the agricultural community. W. T. Johnson at Western Washington and, subsequently, Oregon AES made significant contributions to our understanding of the disease, as did C. A. Herrick and coworkers at Wisconsin AES, J. P. Delaplane and coworkers at Rhode Island AES, and P. P. Levine at Cornell University.  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