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   506篇
  免费   29篇
林业   20篇
农学   14篇
基础科学   8篇
  99篇
综合类   31篇
农作物   14篇
水产渔业   33篇
畜牧兽医   265篇
园艺   13篇
植物保护   38篇
  2024年   6篇
  2023年   4篇
  2022年   8篇
  2021年   17篇
  2020年   18篇
  2019年   16篇
  2018年   20篇
  2017年   14篇
  2016年   8篇
  2015年   17篇
  2014年   17篇
  2013年   26篇
  2012年   37篇
  2011年   35篇
  2010年   28篇
  2009年   30篇
  2008年   40篇
  2007年   43篇
  2006年   29篇
  2005年   27篇
  2004年   21篇
  2003年   21篇
  2002年   17篇
  2001年   2篇
  2000年   4篇
  1999年   2篇
  1998年   1篇
  1997年   4篇
  1996年   3篇
  1995年   3篇
  1992年   1篇
  1991年   3篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1984年   2篇
  1983年   1篇
  1982年   1篇
  1978年   1篇
  1973年   3篇
  1972年   1篇
  1941年   1篇
排序方式: 共有535条查询结果,搜索用时 15 毫秒
101.
102.
103.
A study was carried out in southern Italy to determine the role of some factors in favouring Heterobasidion annosum s. l. spread and damage in eight Silver-fir (Abies alba Mill.) forests. All the studied stands were colonised by H. abietinum. The presence of the fungus (as carpophores on colonised wood) was detected by means of transects and varied from 7.0 to 56.0% of trees. Stand history, precipitation and forest origin, analysed by the χ2-test, had a significant effect on rot severity. Damage was more severe in stands more xerophytic where the woods were planted on pasturelands.  相似文献   
104.
Food-caching western scrub-jays keep track of who was watching when   总被引:1,自引:0,他引:1  
Western scrub-jays (Aphelocoma californica) hide food caches for future consumption, steal others' caches, and engage in tactics to minimize the chance that their own caches will be stolen. We show that scrub-jays remember which individual watched them during particular caching events and alter their recaching behavior accordingly. We found no evidence to suggest that a storer's use of cache protection tactics is cued by the observer's behavior.  相似文献   
105.
Four new acyclic diterpene glycosides named capsianosides (1-4), together with 12 known compounds, were isolated from the fresh sweet pepper fruits of Capsicum annuum L., a plant used as a vegetable food, spice, and external medicine. The chemical structures of new natural compounds, as well as their absolute configurations, were established by means of spectroscopic data including infrared, high-resolution mass spectrometry, and one- and two-dimensional nuclear magnetic resonance and by chemical derivatization. The known capsidiol (11) showed bacteriostatic properties in vitro against Helicobacter pylori with a minimum inhibitory concentration (MIC) of 200 microg/mL when compared with the commercial drug metronidazole (MIC, 250 microg/mL). Some purified components were also tested for their antioxidant activities.  相似文献   
106.
There has long been a focus in urban landscape planning and design on the creation of highquality public spaces, or place-making. Large amounts of capital continue to be spent on creating such spaces without adequate thought or resources for their long-term maintenance and management of public spaces, or place-keeping.While there may be continued policy rhetoric about the importance of place-keeping, particularly as public spaces are recognised for their important contribution to health, wellbeing, biodiversity and also their economic value, this has not however been supported in practice. There are examples in many cities where public spaces are subject to poor management and maintenance practices. This is clearly visible where vandalism, litter and damage to facilities and equipment occur, and people no longer feel safe or comfortable.This paper argues that this uneven focus on place-keeping is not only due to a lack of resources but also a lack of understanding of the concept, its complexity and the wide implications it has for users, practitioners and policymakers. The paper aims to address this gap in knowledge by providing a detailed exploration and definition of place-keeping within the urban context. Place-keeping is not simply about the physical environment, its design and maintenance, but also encompasses the interrelated and non-physical dimensions of partnerships, governance, funding, policy and evaluation.  相似文献   
107.
To date, limited information is available on the ability of 'Hobi'-like pestiviruses (putative bovine viral diarrhoea 3) to infect and cause disease in animal species traditionally affected by pestiviruses. In order to obtain new insights into host range and pathogenic potential of this atypical pestivirus, BVDV-seronegative calves (n=5), lambs (n=5) and piglets (n=5) were experimentally infected with the European 'Hobi'-like strain Italy-1/10-1, whereas two animals per species served as uninfected controls. Appearance of clinical signs, leukopenia, viremia, viral shedding and seroconversion were monitored for 28 days post-infection. Calves and lambs were successfully infected, displaying respiratory signs (nasal discharge), moderate hyperthermia and leukopenia, viremia and viral shedding through the nasal and faecal routes. Antibody responses were observed in both animal species by ELISA and virus neutralisation assays. In contrast, inoculated piglets did not display any clinical signs nor leukopenia and viral RNA was not detected in any biological samples. Nevertheless, the presence of detectable antibodies by virus neutralisation accounted for a successful, albeit limited infection of these animals.  相似文献   
108.
The aim of this study was to describe the tenovaginoscopic approach to the bovine common digital flexor tendon sheath (CDFTS). A comparative anatomical, ultrasonographic and endoscopic study was undertaken using 26 healthy cadaver feet from adult dairy cows. Tenovaginoscopy was performed using a rigid, 30° arthroscope (length 18 cm; outer diameter 4mm) enabling a direct view of the synovial cavity and the following structures: digital flexor tendons, digital annular ligaments, lateral and medial pouches, three mesotendons, the vinculum of the superficial digital flexor tendon, and a slot-shaped opening in the manicaflexoria of the hind feet. Additionally, four clinical cases of septic tenosynovitis treated with lavage under tenovaginoscopic control were examined. Tenovaginoscopy represents a feasible, minimally invasive method for the diagnosis and treatment of septic tenosynovitis of the CDFTS, which allows the degree of alterations of the normal structures to be evaluated.  相似文献   
109.
A study was carried out to assess the efficacy and the economic profit of prophylactic treatment against Isopsora suis with toltrazuril or with a sulfamethazine/trimethoprim combination in piglets from an intensive pig farm. Thirty-one litters were included in study. Eight litters were treated once with toltrazuril (20 mg/kg b.w.) at 3 days of age (Toltra group); 8 litters were treated with the sulphonamide combination (sodium sulfamethazine 35 mg and trimethoprim 7 mg/kg b.w.) for 3 consecutive days starting at 3 days of age (Sulfa group), and 15 litters were untreated (control group). Counts of oocyst per gram on pooled feces sampled from each litter were carried out on Days 7, 14, 21 and 28 and diarrhea was registered daily from pooled samples. Piglets were weighed on Days 1, 7 and 28 and mean weight gain (WG) and daily weight gain (DWG) were evaluated. The economic profit of treatment was evaluated comparing the WG of piglets of each treatment group from the day of birth to Day 28. On Days 14, 21 and 28, toltrazuril showed a better efficacy in controlling fecal oocyst output, diarrhea and weight gain compared with sulphamidic treatment (P < 0.001). The budgeting analysis showed a return of economic benefit of € 0.915 per toltrazuril-treated piglets and an additional cost of € 1.155 per sulphonamide-treated piglets.  相似文献   
110.
This paper reports the clinical findings, diagnostic imaging, surgical management, and necropsy of an unusual case of jejuno-jejunal intussusception in a calf that was diagnosed with the use of ultrasonography, and treated surgically by resection and end-to-end anastomosis. The calf fatally relapsed 8 d after laparotomy. Necropsy and histology revealed enteritis and myenteric ganglionitis.  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