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   223篇
  免费   16篇
林业   13篇
农学   5篇
基础科学   5篇
  65篇
综合类   6篇
农作物   17篇
水产渔业   41篇
畜牧兽医   75篇
园艺   6篇
植物保护   6篇
  2023年   2篇
  2022年   5篇
  2021年   1篇
  2020年   3篇
  2019年   10篇
  2018年   14篇
  2017年   13篇
  2016年   13篇
  2015年   4篇
  2014年   17篇
  2013年   17篇
  2012年   11篇
  2011年   15篇
  2010年   15篇
  2009年   13篇
  2008年   7篇
  2007年   8篇
  2006年   10篇
  2005年   9篇
  2004年   6篇
  2003年   3篇
  2002年   6篇
  2001年   2篇
  1999年   3篇
  1998年   3篇
  1997年   2篇
  1996年   3篇
  1995年   3篇
  1994年   3篇
  1993年   2篇
  1991年   3篇
  1990年   3篇
  1989年   1篇
  1988年   2篇
  1987年   2篇
  1984年   1篇
  1981年   2篇
  1979年   1篇
  1971年   1篇
排序方式: 共有239条查询结果,搜索用时 15 毫秒
151.
152.
The Pabdah catfish, Ompok pabda, was successfully spawned with the synthetic hormone Ovatide at two different doses (0.4 and 0.6 ml/kg of body weight of female). The latency period was 9–10 h at 0.6 ml compared to 10–12 h at 0.4 ml kg?1 of body weight. All the females spawned successfully. Average rate of fertilization (75.5 %) and hatching (60.5%) was higher with a dose of 0.6 ml kg?1, while lower fertilization (65.1%) and hatching rate (45%) were observed at 0.3 ml kg?1 of body weight. Fecundity ranged from 80–130 eggs gm?1 body weight of female. Eggs hatched between 12–14 h after spawning at a water temperature 28°–32°C. The mean egg diameter was 0.95 ± 0.15 mm.  相似文献   
153.
Vaccines for bluetongue   总被引:1,自引:0,他引:1  
Isolation of 8 serotypes of bluetongue virus (BTV) in Australia has led to widespread debate on how to prepare for an outbreak of bluetongue disease and the type of vaccine best suited to control bluetongue in Australia. This article describes the vaccine options under consideration by research workers and animal health administrators. The most widely discussed options are live attenuated virus, killed virus and virus-like particles (VLP) generated by recombinant baculoviruses. Attenuated virus vaccines are cheap and easy to produce and are administered in a single dose. They replicate in sheep without causing significant clinical effects and provide protection against challenge with virulent virus of the same serotype. The possibility that insects could acquire vaccine virus by feeding on vaccinated animals and transmit it to sheep or cattle cannot be eliminated. This poses a risk because attenuated viruses are teratogenic if ewes are infected in the first half of pregnancy. In addition, vaccine virus replication in insects and ruminants may lead to a reversion to virulence. Killed virus vaccines have been shown to be efficacious in small laboratory trials and cannot be transmitted to other animals in the field, but are significantly more expensive to produce than attenuated viruses and require at least 2 doses with adjuvant to elicit an immune response. More work is needed to properly assess their effectiveness and determine their cost of production. Recombinant VLP contain the 4 major structural proteins of BTV but no nucleic acid. VLP are relatively easy to isolate, but it is unlikely that the purification methods currently used in laboratories will be adapted for use commercially. Despite the enthusiasm of recent years, little commercial progress appears to have been made. Although scientific research in Australia and overseas has provided a number of options for development of bluetongue vaccines, the decisions on which to use in an outbreak are complex and will require, not only consideration of factors discussed here, but also agreement from industry and government.  相似文献   
154.
1. The major objective of this study was to examine the influence of 24-h storage of semen at low temperature on semen characteristics and fertilising ability of spermatozoa in two native breeds (Kadaknath-KN, Aseel Peela-AP) and White Leghorn (WL) chicken. 2. Various physical and biochemical properties of freshly ejaculated semen of KN and AP were investigated. Fertility was examined in freshly-ejaculated as well as 24-h-stored (3°C) semen diluted (1:3) with Beltsville Poultry Semen Extender. 3. No significant difference was observed in sperm motility among the different breeds whereas live counts were higher in WL than the native breeds. Body weight, semen volume and sperm concentration were highest in AP, followed by KN and WL. A similar trend was observed in the percentage of dead and morphologically-abnormal spermatozoa. 4. The activity of acid and alkaline phosphatase in seminal plasma were higher in WL than KN, whereas the opposite trend was recorded for glutamic oxaloacetic and pyruvic transaminases. The cholesterol content of semen was highest in AP, followed by KN and WL. Cholesterol was much lower in seminal plasma compared with whole semen but there were no differences between breeds. Mean values of the methylene blue reduction time test were higher in WL than in the native breeds. 5. Fertility and hatchability, using freshly-diluted semen, were poorer in the native breeds than in WL. The pattern of fertility deteriorated further, especially in native fowls, when the birds were inseminated with 24-h-stored semen. 6. In conclusion, variation in physical and biochemical characteristics of semen in native breeds compared to WL correlated with poor fertility after short-term storage of semen.  相似文献   
155.
156.
A computational exercise was undertaken to quantify the percent N derived from atmosphere %Ndfa) in soybean and consequent N benefit from biological N2‐fixation process annually accrued to the soil by the soybean crop using average annual N‐input/‐output balance sheet from a 7 yr old soybean‐wheat continuous rotational experiment on a Typic Haplustert. The experiment was conducted with 16 treatments comprised of combinations of four annual rates of farmyard manure (FYM ? 0, 4, 8, and 16 t ha–1) and four annual rates of fertilizer N (? 0, 72.5, 145, and 230 kg N ha–1) applications. The estimated N contributed through residual biomass of soybean (RBNS) consisting of leaf fall, root, nodules, and rhizodeposition varied in the ranges of 7.02–16.94, 11.65–28.83, 3.31–8.91, and 11.3–23.8 kg N ha–1 yr–1, respectively. A linear relationship was observed between RBNS and harvested biomass N (HBNS) of soybean in the form of RBNS = 0.461 × HBNS – 20.67 (r = 0.989, P < 0.01), indicating that for each 100 kg N assimilated by the harvested biomass of soybean, 25.4 kg N was added to the soil through residual biomass. The Ndfa values ranged between 13% and 81% depending upon the annual rates of application of fertilizer N and FYM. As per the main effects, the %Ndfa declined from 76.4 to 26.0 with the increase in annual fertilizer‐N application from 0 to 230 kg N ha–1, whereas %Ndfa increased from 40.8 to 65.8 with the increase in FYM rates from 0 to 16 t ha–1, respectively. The N benefit from biological N2 fixation accrued to the soil through residual biomass of soybean ranged from 7.6 to 53.7 kg N ha–1 yr–1. The treatments having %Ndfa values higher than 78 showed considerable annual contribution of N from N2 fixation to the soil which were sufficient enough to offset the quantity of N removed from the soil (i.e., native soil N / FYM‐N / fertilizer‐N) with harvested biomass of soybean.  相似文献   
157.
Journal of Pest Science - Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt), is a significant pest of horticultural crops in Australia. The sterile insect technique (SIT) is currently...  相似文献   
158.
Direct observation of percolation in a manganite thin film   总被引:1,自引:0,他引:1  
Upon cooling, the isolated ferromagnetic domains in thin films of La0.33Pr0.34Ca0.33MnO3 start to grow and merge at the metal-insulator transition temperature TP1, leading to a steep drop in resistivity, and continue to grow far below TP1. In contrast, upon warming, the ferromagnetic domain size remains unchanged until near the transition temperature. The jump in the resistivity results from the decrease in the average magnetization. The ferromagnetic domains almost disappear at a temperature TP2 higher than TP1, showing a local magnetic hysteresis in agreement with the resistivity hysteresis. Even well above TP2, some ferromagnetic domains with higher transition temperatures are observed, indicating magnetic inhomogeneity. These results may shed more light on the origin of the magnetoresistance in these materials.  相似文献   
159.
Objectives   To evaluate the implementation and barriers to adoption, among pig producers, of a newly introduced traceability and food safety system in Australia.
Procedure   Implementation of the PigPass national vendor declaration (NVD) linked to an on-farm quality assurance (QA) program was evaluated in May and December 2007 at saleyards and abattoirs in New South Wales, Victoria and Queensland. Four focus group discussions with saleyard producers were held between April and July 2007.
Results   Implementation of the PigPass system in terms of accurate completion of the form and QA accreditation was higher at the export abattoir than at the regional saleyard at the first audit (P < 0.01). Implementation increased at the second audit at the abattoirs, but little change with time was observed at saleyards. Approximately half of the producers at saleyards used photocopied PigPass forms, made at least one error (>64%), and many vendors did not appear to be QA-accredited. During focus groups, producers expressed the view that PigPass implementation improved animal and product traceability. They identified the associated costs and a perceived lack of support by information providers as obstacles for adoption.
Conclusion   Improvement in the implementation of PigPass among producers marketing pigs at export abattoirs was observed during the 8-month period of the study. There is a need for a more uniform message to producers from government agencies on the importance of the PigPass NVD and QA and extension and education targeted toward producers supplying pigs to saleyards and domestic abattoirs to ensure compliance with the traceability requirements.  相似文献   
160.
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