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   677篇
  免费   56篇
  国内免费   1篇
林业   13篇
农学   11篇
  45篇
综合类   132篇
农作物   8篇
水产渔业   7篇
畜牧兽医   487篇
园艺   8篇
植物保护   23篇
  2022年   6篇
  2021年   5篇
  2020年   7篇
  2019年   8篇
  2018年   10篇
  2017年   11篇
  2016年   17篇
  2015年   14篇
  2014年   18篇
  2013年   38篇
  2012年   17篇
  2011年   27篇
  2010年   13篇
  2009年   27篇
  2008年   30篇
  2007年   31篇
  2006年   18篇
  2005年   15篇
  2004年   19篇
  2003年   27篇
  2002年   11篇
  2001年   13篇
  2000年   12篇
  1999年   13篇
  1998年   8篇
  1997年   14篇
  1996年   7篇
  1995年   9篇
  1994年   5篇
  1993年   11篇
  1992年   16篇
  1991年   14篇
  1990年   23篇
  1989年   14篇
  1988年   11篇
  1987年   12篇
  1986年   15篇
  1985年   10篇
  1984年   7篇
  1983年   12篇
  1982年   9篇
  1980年   5篇
  1979年   6篇
  1975年   5篇
  1974年   9篇
  1973年   8篇
  1972年   8篇
  1971年   9篇
  1970年   8篇
  1969年   5篇
排序方式: 共有734条查询结果,搜索用时 31 毫秒
651.
652.
Sugarcane (Saccharum spp.) is increasingly exposed to periodic floods and shallow water tables on Histosols in Florida’s Everglades Agricultural Area (EAA). In the past, when these soils were usually well drained, they provided excess N for sugarcane through microbial oxidation. It is not known if supplemental N would now improve yields because microbial oxidation is reduced by shallow water tables and periodic floods. The purpose of this study was to evaluate the effects of N fertilizer rates on two sugarcane cultivars exposed to a 25-cm water-table depth with and without repeated 2-day floods. Two studies were planted in containers in 2001 and 2002 with two sugarcane cultivars and five equally spaced rates of N fertilizer from 0 to 200 kg ha−1. Leaf, stalk and root weights were reduced by periodic flooding and the magnitude of the reduction sometimes differed between cultivars. Plant weights, leaf chlorophyll content (SPAD) and leaf N content were often highest near an N rate of 100 kg ha−1. Usually, N fertilizer rate did not interact with water treatment. Nitrogen fertilization may be useful for sugarcane exposed to water-table depths of 25 cm with and without 2-day repeated floods on EAA Histosols.  相似文献   
653.
654.
A 13-year-old Morgan gelding was examined for right forelimb lameness and tenosynovitis of the right common carpal sheath of the digital flexor tendons. The horse had moderate right forelimb lameness at the trot and marked effusion of the right common carpal sheath of the digital flexor tendons. Ultrasonographic examination revealed a soft tissue mass within the proximal pouch of the affected tendon sheath, located adjacent to the distal physis of the radius. Cytology and culture of the fluid revealed a sterile, eosinophilic tenosynovitis. Tenoscopic exploration confirmed the presence of a capsulated soft tissue mass. Thecotomy was required to fully debride the mass, which histology revealed to be a mast cell tumour. At 22 months postoperatively, the horse developed mild right forelimb lameness and eosinophilic tenosynovitis because of recurrence of the mastocytoma. Mastocytosis is a possible differential diagnosis in any horse exhibiting lameness associated with tenosynovitis. Surgical excision combined with rest and postoperative intrasynovial and systemic corticosteroids may be palliative.  相似文献   
655.
The United Kingdom’s approach to encouraging environmentally positive behaviour has been three-pronged, through voluntarism, incentives and regulation, and the balance between the approaches has fluctuated over time. Whilst financial incentives and regulatory approaches have been effective in achieving some environmental management behavioural change amongst farmers, ultimately these can be viewed as transient drivers without long-term sustainability. Increasingly, there is interest in ‘nudging’ managers towards voluntary environmentally friendly actions. This approach requires a good understanding of farmers’ willingness and ability to take up environmental activities and the influences on farmer behavioural change. The paper aims to provide insights from 60 qualitative farmer interviews undertaken for a research project into farmers’ willingness and ability to undertake environmental management, particularly focusing on social psychological insights. Furthermore, it explores farmers’ level of engagement with advice and support networks that foster a genuine interest, responsibility and a sense of personal and social norm to sustain high quality environmental outcomes. Two conceptual frameworks are presented for usefully exploring the complex set of inter-relationships that can influence farmers’ willingness to undertake environmental management practices. The research findings show how an in-depth understanding of farmer’s willingness and ability to adopt environmental management practices and their existing level of engagement with advice and support are necessary to develop appropriate engagement approaches to achieve sustained and durable environmental management.  相似文献   
656.
Parasites are an important but neglected component of ecosystems that can be used as indicators of host biology and ecology. In the present study, the metazoan parasite assemblage of Ruvettus pretiosus, an understudied but widely distributed predatory gempylid, caught off South Africa was surveyed. A total of seven parasite taxa, including four new infection records (Bolbosoma capitatum, Rhadinorhynchus sp., Hepatoxylon trichiuri and Anisakis sp.), two new locality records (B. capitatum and Rhipidocotyle sp.) as well as the ectoparasitic copepod Sagum foliaceus and the cestode Tentacularia coryphaenae were recovered from the eight specimens examined.  相似文献   
657.
The reproductive performance of postpartum Santa Inês (SI) and Morada Nova (MN) ewes treated with insulin or progesterone hormones in association with ram effect was evaluated. Ewes from SI (n = 69) and MN (n = 69) breeds were randomly allocated to three groups of each breed (T1—ram effect only; T2—ram effect + insulin; T3—ram effect + progesterone). Progesterone concentrations (ηg/ml; mean ± SD) before and after introduction of rams (n = 6) were 0.51 ± 0.22 and 3.78 ± 0.68 (T1), 0.65 ± 0.21 and 3.77 ± 0.78 (T2) and 0.52 ± 0.21 and 3.84 ± 0.84 (T3) in SI ewes and 0.74 ± 0.19 and 3.71 ± 0.56 (T1), 0.70 ± 0.21 and 3.79 ± 0.75 (T2) and 0.81 ± 0.14 and 3.87 ± 0.80 (T3) in MN ewes, respectively. Thus, lower progesterone concentrations were found before the introduction of rams (p < .05). After the introduction of rams, preovulatory peaks of LH (ηg/ml) occurred at 28 (T1), 44 (T2) and 48 (T3) hr in SI ewes and at 64 (T1), 40 (T2) and 44 (T3) hr in MN ewes. The mean number of ovulations was similar between groups (p > .05), was 1.3 ± 0.51 (T1), 1.5 ± 0.54 (T2) and 1.6 ± 0.51 (T3) in SI ewes and 1.3 ± 0.51 (T1), 1.6 ± 0.51 (T2) and 1.6 ± 0.51 (T3) in MN ewes. In conclusion, the ram effect alone is effective at inducing and synchronizing oestrus in sheep under postpartum anoestrus, irrespective of hormone treatments.  相似文献   
658.
There are rare published reports of atrial fibrillation (AF) in foals, all of which are associated with structural heart disease or within the adaptive period of newborns. This report describes a 3-month-old Thoroughbred filly with AF and a structurally normal heart on echocardiography. Medical cardioversion of the foal's AF was attempted with three 20mg/kg doses of quinidine sulfate therapy without success. Timed, transcutaneous, direct current cardioversion was successfully performed using adhesive patches on the midthorax in conjunction with intravenous procainamide at a total dose of 20mg/kg. A normal sinus rhythm was maintained through discharge from the hospital and at recheck 5 months after cardioversion. Transcutaneous direct current cardioversion presents a feasible alternative to quinidine sulfate or transvenous electrical cardioversion in young or lower body weight equids.  相似文献   
659.
660.
The USDA Agricultural Research Service (ARS) funded a demonstration project (1998-2002) for areawide IPM for stored wheat in Kansas and Oklahoma. This project was a collaboration of researchers at the ARS Grain Marketing and Production Research Center in Manhattan, Kansas, Kansas State University, and Oklahoma State University. The project utilized two elevator networks, one in each state, for a total of 28 grain elevators. These elevators stored approximately 31 million bushels of wheat, which is approximately 1.2% of the annual national production. Stored wheat was followed as it moved from farm to the country elevator and finally to the terminal elevator. During this study, thousands of grain samples were taken in concrete elevator silos. Wheat stored at elevators was frequently infested by several insect species, which sometimes reached high numbers and damaged the grain. Fumigation using aluminum phosphide pellets was the main method for managing these insect pests in elevators in the USA. Fumigation decisions tended to be based on past experience with controlling stored-grain insects, or were calendar based. Integrated pest management (IPM) requires sampling and risk benefit analysis. We found that the best sampling method for estimating insect density, without turning the grain from one bin to another, was the vacuum probe sampler. Decision support software, Stored Grain Advisor Pro (SGA Pro) was developed that interprets insect sampling data, and provides grain managers with a risk analysis report detailing which bins are at low, moderate or high risk for insect-caused economic losses. Insect density was predicted up to three months in the future based on current insect density, grain temperature and moisture. Because sampling costs money, there is a trade-off between frequency of sampling and the cost of fumigation. The insect growth model in SGA Pro reduces the need to sample as often, thereby making the program more cost-effective. SGA Pro was validated during the final year of the areawide program. Based on data from 533 bins, SGA Pro accurately predicted which bins were at low, moderate or high risk. Only in two out of 533 bins did SGA Pro incorrectly predict bins as being low risk and, in both cases, insect density was only high (> two insects kg(-1)) at the surface, which suggested recent immigration. SGA Pro is superior to calendar-based management because it ensures that grain is only treated when insect densities exceed economic thresholds (two insects kg(-1)). This approach will reduce the frequency of fumigation while maintaining high grain quality. Minimizing the use of fumigant improves worker safety and reduces both control costs and harm to the environment.  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