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   2298篇
  免费   181篇
  国内免费   6篇
林业   140篇
农学   40篇
基础科学   19篇
  345篇
综合类   433篇
农作物   50篇
水产渔业   265篇
畜牧兽医   961篇
园艺   76篇
植物保护   156篇
  2023年   19篇
  2022年   19篇
  2021年   54篇
  2020年   62篇
  2019年   84篇
  2018年   77篇
  2017年   88篇
  2016年   65篇
  2015年   57篇
  2014年   71篇
  2013年   102篇
  2012年   148篇
  2011年   194篇
  2010年   125篇
  2009年   76篇
  2008年   149篇
  2007年   168篇
  2006年   132篇
  2005年   147篇
  2004年   152篇
  2003年   136篇
  2002年   97篇
  2001年   32篇
  2000年   20篇
  1999年   13篇
  1998年   8篇
  1997年   9篇
  1996年   14篇
  1995年   19篇
  1994年   12篇
  1993年   4篇
  1992年   13篇
  1991年   15篇
  1990年   10篇
  1989年   17篇
  1988年   8篇
  1987年   6篇
  1986年   11篇
  1985年   10篇
  1984年   6篇
  1983年   3篇
  1981年   3篇
  1978年   3篇
  1977年   3篇
  1976年   4篇
  1975年   2篇
  1973年   2篇
  1967年   3篇
  1966年   2篇
  1965年   2篇
排序方式: 共有2485条查询结果,搜索用时 265 毫秒
31.
Results of preoperative ultrasonography and exploratory laparotomy were reviewed retrospectively in a series of 100 small animals to assess the agreement between ultrasonographic and surgical findings and to identify abdominal lesions likely to be missed by ultrasonography. Good agreement occurred between ultrasound reports and surgical reports in 64% of the animals, which supported the use of ultrasonography in potential surgical candidates. A major discrepancy was observed between the ultrasound report and surgical findings in 25% of the animals. Of the various types of pathology encountered in the study, gastrointestinal ulceration or perforation was the most likely lesion to be missed by ultrasonography.  相似文献   
32.
Chorioptes sp. mite infestation is increasingly recognized as a cause of skin disease in New World camelids and there is a need for an effective treatment protocol to eliminate herd infestation. In this field trial, eprinomectin applied topically at the rate of 0.5 mg kg(-1) weekly for 10 weeks was found to be ineffective in a herd of 12 llamas and 16 alpacas.  相似文献   
33.
Heartworm infection in dogs and cats in the western United States is a fairly new phenomenon, and for this reason it is often considered to be of minimal significance.The purpose of this survey was to collect data from 11 western states (Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming) in an effort to assess awareness of heartworm disease and identify areas in which improvement in understanding is needed. To accomplish this goal, veterinary clinics and hospitals in these states were sent a one-page survey in early 2006. The results of the survey demonstrate that cases of heartworm disease have been reported in all 11 states, illustrating the importance of annual testing and the routine use of preventives.  相似文献   
34.
BACKGROUND: Omeprazole reduces the severity of exercise-induced gastritis but not the prevalence of gastric lesions in sled dogs. The frequent feeding of sled dogs during competition likely results in decreased absorption of omeprazole and, thereby, decreased efficacy. HYPOTHESIS: Famotidine, a histamine-2 blocker with good bioavailability in the presence of food, would reduce the incidence and severity of exercise-induced gastric disease in sled dogs. ANIMALS: Sixteen fit Alaskan sled dogs (4 female, 12 male, all intact, age 2-6 years). METHODS: Dogs were randomly assigned to treatment (22 mg famotidine PO q24h) or control groups (n = 8 per group). Famotidine was administered with a meal to the treatment group once daily for 7 days before a challenge and once during exercise. Control dogs were fed an identical diet as the principal group. The 16 dog team completed a 100-mile exercise challenge in 18 hours. A gastroscopy was performed 24 hours after the challenge. The appearance of the mucosa was scored by an individual by using a scoring system. RESULTS: Treatment with famotidine significantly reduced the severity score compared with control (P = .0004). No adverse effects of treatment were reported. CONCLUSIONS AND CLINICAL RELEVANCE: Famotidine is effective in reducing the severity of exercise-induced gastric disease in racing Alaskan sled dogs, with minimal to no adverse effects, and may be recommended for prophylactic use in short distance races.  相似文献   
35.
36.
River systems throughout arid regions worldwide have been heavily impacted by human activities, resulting in long‐term ecological consequences. The lower Pecos River in the Trans‐Pecos region of Texas is no exception, having undergone anthropogenic changes that include decreased flow, elevated salinity, species loss and species invasion. We compared historical and contemporary fish assemblage attributes from the Pecos River at local (site‐specific) and regional (Trans‐Pecos region) scales across a 24‐year time period. Fish assemblage data were collected in October 1987 and 2011, by seining at 15 sites spanning 430 km of the river in Texas. Additionally, we examined contemporary environmental conditions to determine species–environment relationships. We found that fish assemblages were significantly different between time periods, likely due to increased salinisation in the upper half of the study region. Decreased species richness, species replacement and increases in euryhaline species were documented in the upstream sites. Freshwater springs lower the salinity and maintain flows in the downstream reach, allowing for maintenance of the native fish fauna. Careful management of regional aquifers, irrigation practices and petroleum waste water will be necessary for protecting biodiversity and environmental flows in the lower Pecos River.  相似文献   
37.
Environmental pressure, land utilization, and economic feasibility have resulted in the development of recirculating aquaculture systems (RAS). For many RAS, sludge is collected and washed from the system to waste stabilization ponds (WSPs). However, disposal of brackishwater aquaculture sludge into WSP is often prohibited because the high salinity can interfere with treatment. Moreover, there are problems associated with WSPs because of elevated salt content, such as the common practice of reusing treated water and land application of stabilized sludge. We tested and compared the treatment of brackishwater aquaculture sludge in an upflow anaerobic sludge blanket (UASB) reactor as an alternative to a WSP. In UASB, wastewater flows upward through a blanket of granular sludge and is treated by anaerobic micro‐organisms. Reduction in organic matter and 5‐d biochemical oxygen demand by 97 and 91%, respectively, was achieved in a UASB as compared to corresponding reductions of 22 and 41% in a WSP. During the UASB digestion process, methane is produced and recovered. Overall, a reduction in potential environmentally harmful factors such as salinization, land requirements, greenhouse gas emissions, as well as transportation costs are achieved, making the UASB reactor an attractive possible alternative for saline aquaculture sludge management.  相似文献   
38.
The discovery and development of the pyrethroid insecticides represents a major advance in the techniques of crop protection and disease vector control. These compounds combine outstanding efficacy against a broad spectrum of noxious insects with low toxicity to birds and mammals. This paper considers the effects of pyrethroids on other components of the terrestrial non-target fauna, with particular reference to effects on ‘beneficial’ organisms, including natural pest-control agents, pollinators, and organisms responsible for the maintenance of soil structure and fertility. This paper uses laboratory and field data to identify which groups of organisms may be potentially at risk from the use of pyrethroids, and draws on extensive field data to consider the significance of such hazards under conditions of normal use. Emphasis will be placed throughout on the evaluation of these compounds under practical conditions, including both crop and non-crop usages. Limitations to, and opportunities for, the use of pyrethroids are discussed, and the potential for further development is considered.  相似文献   
39.
The insecticidal properties of twelve pyrethroid preparations impregnated into polyester netting were compared, before and after washing, with a view to assessing their suitability for treating bednets (mosquito nets) in the field. Bioassays were carried out by exposing the mosquitoes, Anopheles gambiae Giles sensu stricto andAedes aegypti L. to netting with two concentrations of insecticide, on washed and unwashed samples, for 30 s and 3 min at different times after impregnation. Mortality was recorded after 24 h. Permethrin applied at 97°C at pH 3.4 resulted in increased uptake by polyester fibres. The performance of most insecticides on unwashed netting had not declined appreciably 12 weeks after impregnation. However, all the insecticides were depleted by washing. The treatments with best insecticidal activity after washing were cypermethrin, lambda-cyhalothrin applied at ambient temperature and normal pH and permethrin applied in a hot acid solution.  相似文献   
40.
Ten dairy cows were separated into two groups of five. One group was ear tagged with a PVC ear tag containing 8-5 g kg?1 cypermethrin in each ear. A PVC strip impregnated with the same quantity of cypermethrin was attached to the tail of each cow in the other group. The concentration of cypermethrin in hair samples from the neck, flanks and the anterior, sides and the posterior of the udder was measured for a period of 10 weeks after application. Concentrations were found to be high in those body areas nearest to the points of application, moderate on the flanks but low on the front and sides of the udder.  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