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   1544篇
  免费   96篇
林业   59篇
农学   19篇
基础科学   17篇
  193篇
综合类   315篇
农作物   43篇
水产渔业   40篇
畜牧兽医   844篇
园艺   32篇
植物保护   78篇
  2021年   12篇
  2020年   28篇
  2019年   19篇
  2018年   21篇
  2017年   24篇
  2016年   35篇
  2015年   17篇
  2014年   25篇
  2013年   51篇
  2012年   53篇
  2011年   66篇
  2010年   35篇
  2009年   31篇
  2008年   62篇
  2007年   53篇
  2006年   47篇
  2005年   45篇
  2004年   51篇
  2003年   51篇
  2002年   45篇
  2001年   49篇
  2000年   43篇
  1999年   31篇
  1998年   21篇
  1997年   28篇
  1996年   18篇
  1993年   15篇
  1992年   22篇
  1991年   23篇
  1990年   26篇
  1989年   47篇
  1988年   36篇
  1987年   36篇
  1986年   37篇
  1985年   19篇
  1984年   18篇
  1983年   22篇
  1982年   15篇
  1980年   11篇
  1979年   19篇
  1978年   16篇
  1977年   15篇
  1976年   17篇
  1974年   17篇
  1973年   19篇
  1972年   23篇
  1971年   11篇
  1970年   18篇
  1969年   12篇
  1968年   12篇
排序方式: 共有1640条查询结果,搜索用时 15 毫秒
61.
Three mixed-breed dogs and a Boxer dog with nodular dermatofibrosis are described. The three mixed breed dogs had concurrent renal epithelial cysts ( n  = 2) or renal cystadenomas ( n  = 1); these lesions were visualized antemortem on ultrasonographic examination. One of these dogs was a 7-year-old Labrador Retriever-Gordon Setter mixed breed which survived 5 years after diagnosis, and was euthanized for unrelated causes. The Boxer dog had renal cystic adenomatous hyperplasia and renal cystadenocarcinomas which were not visualized on ultrasonographic examination but were diagnosed at necropsy.  相似文献   
62.
The surgical repair of oesophageal hiatal herniation in five dogs is described. The initial presenting signs included regurgitation, vomiting, hypersalivation, anorexia, coughing, dyspnoea and exercise intolerance. Diagnosis was based upon the clinical signs, plain radiography and contrast fluoroscopic examination. The hernias were corrected by a hiatal plication technique which moved the diaphragmatic oesophagus to a new anatomical position, a 360° oesophagopexy and a proximal fundic gastropexy. Surgical results were considered excellent in all cases.  相似文献   
63.
Four cases of extrahepatic biliary tract surgery in the cat are described. The causes of the disease were inflammation of the gallbladder, distal common bile duct (CBD) or major duodenal papilla, and traumatic avulsion of the CBD. Bile peritonitis was present in two of the cats. Biliary enterostomy was performed in three cats, two of which were euthanased at five weeks and three months postsurgery; the third was alive at the time of writing, four months postsurgery. Cholecystectomy was curative in one cat. A literature review reveals high early mortality following biliary diversion, with only 50 per cent of cases surviving more than two weeks, and 23 per cent surviving more than six months. Surviving cats had repeated intermittent vomiting and anorexia that responded to antibiotics. No postoperative mortality was seen when biliary diversion was avoided. Whenever biliary enterostomy or temporary diversion methods are performed, a poorer prognosis should be offered due to the increased likelihood of postoperative complications and mortality.  相似文献   
64.
65.
Agricultural, industrial and domestic use of surfactants leads to the entry of these compounds into terrestrial and aquatic ecosystems. Synthetic surfactants vary significantly in structure, but most consist of alkyl or alkylphenol groups attached to nonionic or anionic hydrophilic moieties. Continued use of these compounds is usually justified on the basis that they do not cause pollution problems because they undergo biodegradation by micro-organisms present in soils and surface waters. In accomplishing biodegradation, micro-organisms, predominantly bacteria, are exploiting these potentially useful resources of reduced carbon to derive energy and support growth in situations which are otherwise frequently oligotrophic. This paper reviews aspects of surfactant biodegradation, especially in relation to alcohol and alkylphenol ethoxylates used extensively as adjuvants for agrochemicals. In principle, bacteria can employ two strategies to gain access to the aliphatic chains in alcohol ethoxylate surfactants: separation of the hydrophobic chain from the hydrophile (central fission), or direct attack on the -terminal of the alkyl chain of the intact surfactant. Direct exo-cleavage of ethylene glycol units from the polyethylene glycol (PEG) chain also provides a third route to assimilable carbon. In pure cultures of known degraders or in mined environmental samples, all three strategies are exploited, some even within the same organism. Central fission occurs predominantly at the alkyl-ether bond, but may also occur within the PEG chain itself, thus producing various glycol intermediates which accumulate in pure cultures but appear only transiently in mixed environmental samples. Against this background, the relative resistance of some alkylphenol ethoxylates to biodegradation can be assessed in mechanistic terms. The steric bulk of the aryl nucleus effectively eliminates the central fission pathway. Moreover, some alkyl phenol ethoxylates contain branched alkyl chains which restrict ω-β-oxidation. As a result, ethoxylate shortening appears to be the major course of biodegradation observed so far. Not surprisingly, these surfactants are observed to undergo extensive primary biodegradation (removal of surfactant properties) but relatively restricted ultimate degradation to carbon dioxide and normal cell components.  相似文献   
66.
67.
68.
Pruritus is a common complaint in equine medicine. While pruritus in most horses is due to ectoparasites (midges, flies, mites) or environmental allergens (pollens, barn dust, moulds, etc.), other causes such as staphylococcal or fungal infections, vasculitis, and internal organ dysfunction should not be overlooked. In a rational approach to the pruritic horse, history and physical examination become very important as a guide to choosing diagnostic tests.  相似文献   
69.
Urban brown rats (Rattus norvegicus) carry microbial human pathogens but their role as reservoir hosts for helminths of public health importance is less well known. In this study, 42 brown rats trapped on Merseyside were subject to thorough combined helminthological and pathohistological post‐mortem examination. Eggs of the rodent‐borne zoonotic nematode Calodium hepaticum were initially detected in histological sections of the livers of 9.5% of rats, but overall diagnostic sensitivity increased to 16.6% when entire liver tissue was disrupted and the resulting filtrates were examined for released eggs. In their rat host, mainly trapped inside the dockland, infections with C. hepaticum were associated with a chronic multifocal pyogranulomatous hepatitis with intralesional eggs and peripheral fibrosis. Mean intensity of hepatic C. hepaticum egg infections was 1041 eggs. This is the first report of C. hepaticum in an urban brown rat population in the UK and provides original data for liver egg burdens in this abundant commensal rodent. The zoonotic cestode Rodentolepis nana had a prevalence of infection of 14.3%. Rodent‐specific, non‐zoonotic helminths found were the spiruroid Mastophorus muris (16.0%) in the stomach, the trichuroid Trichosomoides crassicauda in the urinary bladder (31.0%); the ascarid Heterakis spumosa was the commonest helminth of the large intestine (76.2%). Many millions of brown rats inhabit cities and rural areas of the UK, and the infective stages of the zoonotic worm species, particularly C. hepaticum, are likely to be widely distributed in the environment presenting a threat to public health.  相似文献   
70.
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