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   433篇
  免费   22篇
林业   27篇
农学   1篇
基础科学   1篇
  22篇
综合类   59篇
农作物   48篇
水产渔业   38篇
畜牧兽医   242篇
园艺   4篇
植物保护   13篇
  2021年   6篇
  2020年   3篇
  2019年   6篇
  2018年   4篇
  2017年   5篇
  2016年   7篇
  2015年   7篇
  2014年   12篇
  2013年   15篇
  2012年   15篇
  2011年   10篇
  2010年   13篇
  2009年   9篇
  2008年   18篇
  2007年   19篇
  2006年   21篇
  2005年   17篇
  2004年   17篇
  2003年   18篇
  2002年   10篇
  2001年   10篇
  2000年   9篇
  1999年   10篇
  1998年   13篇
  1997年   7篇
  1996年   7篇
  1995年   7篇
  1994年   5篇
  1993年   8篇
  1992年   10篇
  1991年   4篇
  1990年   8篇
  1989年   8篇
  1988年   5篇
  1987年   7篇
  1986年   10篇
  1985年   6篇
  1984年   4篇
  1983年   3篇
  1978年   4篇
  1973年   4篇
  1971年   4篇
  1969年   3篇
  1967年   3篇
  1966年   3篇
  1962年   3篇
  1959年   3篇
  1954年   3篇
  1947年   3篇
  1941年   3篇
排序方式: 共有455条查询结果,搜索用时 31 毫秒
81.
A useful approach for evaluating antitussive drugs in humans is to determine the sensitivity of the cough reflex to a standard challenge. The purpose of this study was to determine if methods used to induce coughing in humans would be effective when used on awake, untrained, healthy dogs for future application in therapeutic trials involving dogs with spontaneous disease. Methods tested were: mechanically stimulating the trachea by digital compression as well as by vibration from an electric shaver, neck massager, and palm sander (11 dogs), and administering nebulized irritant (3000 μM capsaicin), acidic (1 M citric acid), and hypotonic (deionized water) solutions using face masks (4 dogs). The threshold for success was defined as induction of at least 2 moderate or strong coughs in at least 75% of the dogs. None of the methods tested was successful. Digital compression induced soft (n = 2) or moderate (n = 1) coughing in 3 of 11 dogs tested. Nebulization of citric acid induced 1 soft cough in 1 of 4 dogs. It was concluded that coughing cannot be successfully induced in awake, healthy dogs using methods that are successful in humans. Other strategies must be developed so that cough sensitivity can be objectively and non-invasively measured in dogs for clinical research purposes.  相似文献   
82.
83.
Granular aldicarb and carbofuran, systemic carbamate insecticides, were applied at 3 lbs active per acre to compare their control of the meadow nematode (Pratylenchus penetrans). These systemic pesticides were applied either in two bands 2–3 inches from both sides of and at the lower plane of the seed-piece or in one band 4–5 inches wide and 1/2 inch above the seed. Two months after planting, nematode populations were greatly reduced in soil and roots from plots treated with either chemical and with both placement methods. Aldicarb provided effective control longer into the growing season than did carbofuran. When compared with carbofuran, aldicarb-treated potao plants lived longer and produced a greater increase in yield over the untreated plots. Yield increases were greater when either systemic was applied in side bands than when placed over the seed.  相似文献   
84.
85.
The application of nematicides resulted in increased potato yields, and populations ofPratylenchus penetrans were lower for 3 years after application; but longevity of benefits of fumigating potato fields varied with the kind and amount of nematicide, application methods and with growing conditions after fumigation. Fumigation of two fields in the fall of 1965 with Vorlex, Telone, D-D, and mixtures of chloropicrin with Telone or D-D resulted in 70% to 90% control of the meadow nematode,P. penetrans, after two crops in one field, and 50% to 70% control after three crops in another. Yield increases of Kennebec potatoes averaged 42% and 16% in successive crops in the first field and yield increases of Katahdin potatoes averaged 13%, 22% and 16% in three successive crops in the other field. Fumigation resulted in 30 to 70% less vascular browning in tubers in the first two crops but there was no effect in the third crop. There was no effect on black scurf in any crop. Root injury varied proportionally with populations ofP. penetrans in roots in 1967. Populations ofP. penetrans regained injurious levels in three other fields after one crop when abundant root growth in moist 1967 followed spring fumigation with Telone and D-D. Under poor conditions for sealing of the soil following fumigation in the spring of 1968, counts ofP. penetrans collected at different soil depths after fumigation showed excellent kill below 3 inches and poorer kill in the upper 2 inches of soil.  相似文献   
86.
87.
88.
A 4-year-old female donkey residing in an open field in Indiana was admitted for evaluation of facial lesions of 2 years duration. Cytologic and histologic examination of exudate and tissue from the lesions revealed a pyogranulomatous inflammatory reaction with numerous yeasts. Sporothrix schenckii was suspected to be the infectious agent; however, multiple culture attempts did not provide positive identification of the organism. Serologic examination supported infection with S. schenckii. A specific direct immunofluorescent antibody test performed on paraffin-embedded tissue sections confirmed the organism as S. schenckii. Clinical signs resolved after appropriate iodide therapy.  相似文献   
89.
In 1999, some countries are developing and effectively applying economic instruments for environmental protection and natural resource management, whilst others are relying on command and control regulatory procedures under-enforced by sometimes inadequately trained and motivated enforcement officers. This paper considers the current and future role of economic instruments as policy instruments for use by governments. In many developed countries, past over-regulation allied to a serious shortfall of experienced environmental enforcers required regulatory regimes to be supplemented by well targeted economic instruments and green taxes. Their application to countries which do not have developed environmental control systems is more questionable. The purported threats of the longer term effects of global warming, damage to the ozone layer and an apparent loss of biodiversity have led environmentalists to adopt the so-called precautionary principle. Sustainable development has added to the pressures for further national and transfrontier legislation. The challenge facing policymakers, therefore, is to design policies to enable market forces to operate in the environmental sphere, for example through a system of pollution charges, principally intended to promote greater environmental efficiency. These charging systems can be of many kinds but their main defining feature is their reliance on markets and the price mechanism to internalise environmental externalities, thereby attempting to make polluters pay through facing the full social costs of their activities. Some of the applications of these charging systems, financial and fiscal instruments and tradable emission systems are explained and illustrated.  相似文献   
90.
The distribution of infectious salmon anaemia (ISA) was examined among 80 cages from three Atlantic salmon grow-out farms in Maine, USA that were stocked with smolts from a single hatchery. Cage-level disease was broadly defined as one or more moribund fish testing positive for infectious salmon anaemia virus (ISAV) by RT-PCR and a second confirmatory test (IFAT, culture or genotype sequence). Spatio-temporal and cage-level risks were explored using logistic regression and survival analysis. Non-spatial risk factors associated with ISA, or shortened survival time to disease, included increased predation, trucking company choice for smolt transfers, a finely-sedimented benthic substrate, and smaller average size of smolts at stocking. Univariable analysis identified the time-dependent spatial factor 'adjacency to newly infected cages' to be predictive of new infection in neighbouring cages 11-12 weeks later. However, none of the spatial factors, or their lags retained relevance in multiple-variable models. The results suggest a diffuse distribution of virus exposure throughout infected sites, with host-susceptibility factors probably influencing disease manifestation in individual cages. The narrow focus of the current study may limit application of the findings to other sites and year-classes. However, these data support the relevance of husbandry efforts to optimize fish health in regions affected by ISAV.  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