全文获取类型
收费全文 | 445篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
林业 | 21篇 |
农学 | 4篇 |
54篇 | |
综合类 | 73篇 |
农作物 | 7篇 |
水产渔业 | 15篇 |
畜牧兽医 | 271篇 |
园艺 | 5篇 |
植物保护 | 18篇 |
出版年
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 9篇 |
2016年 | 8篇 |
2015年 | 4篇 |
2013年 | 10篇 |
2012年 | 9篇 |
2011年 | 24篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 18篇 |
2007年 | 29篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 9篇 |
2002年 | 13篇 |
2001年 | 9篇 |
2000年 | 23篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1970年 | 8篇 |
1969年 | 6篇 |
1968年 | 3篇 |
1927年 | 2篇 |
1885年 | 2篇 |
排序方式: 共有468条查询结果,搜索用时 0 毫秒
461.
Climate change is predicted to become a major threat to biodiversity in the 21st century, but accurate predictions and effective solutions have proved difficult to formulate. Alarming predictions have come from a rather narrow methodological base, but a new, integrated science of climate-change biodiversity assessment is emerging, based on multiple sources and approaches. Drawing on evidence from paleoecological observations, recent phenological and microevolutionary responses, experiments, and computational models, we review the insights that different approaches bring to anticipating and managing the biodiversity consequences of climate change, including the extent of species' natural resilience. We introduce a framework that uses information from different sources to identify vulnerability and to support the design of conservation responses. Although much of the information reviewed is on species, our framework and conclusions are also applicable to ecosystems, habitats, ecological communities, and genetic diversity, whether terrestrial, marine, or fresh water. 相似文献
462.
Omar G Johnson KR Hickey LJ Robertson PB Dawson MR Barnosky CW 《Science (New York, N.Y.)》1987,237(4822):1603-1605
Haughton Astrobleme is a major extraterrestrial impact structure located on Devon Island in the Canadian Arctic Archipelago, Northwest Territories. Apatite grains separated from shocked Precambrian gneiss contained in a polymict breccia from the center of the astrobleme yielded a fission-track date of 22.4 million +/- 1.4 million years before the present or early Miocene (Aquitanian). This provides a date for the impact event and an upper limit on the age of crater-filling lake sediments and a flora and vertebrate fauna occurring in them. A geologically precise date for these fossils provides an important biostratigraphic reference point for interpreting the biotic evolution of the Arctic. 相似文献
463.
Gregory D Roach Kathryn J Reid Sally Ferguson Drew Dawson 《Journal of circadian rhythms》2006,4(1):8-5
Background
The aim of the study was to examine the role that melatonin production plays in the regulation of sleep consolidation in a population of shiftworkers working and sleeping in their natural environments. 相似文献464.
S Dawson K Willoughby R M Gaskell G Wood W S Chalmers 《Journal of Feline Medicine and Surgery》2001,3(1):17-22
A trivalent (feline panleucopenia, feline herpesvirus, feline calicivirus), modified live, commercially available cat vaccine was used at either 6, 9 and 12 weeks of age (early schedule) or 9 and 12 weeks of age (conventional schedule), and the serological response to vaccination was assessed. The level of maternally derived antibody present at 6 weeks of age was also established. The use of early vaccination at 6 weeks of age induced an antibody response to each virus by 9 weeks of age in a significant proportion of kittens compared with unvaccinated littermates. There was no difference between the conventionally and early-vaccinated groups in terms of antibody response to any antigen by 12 and 15 weeks of age. 相似文献
465.
Sahlu T Dawson LJ Gipson TA Hart SP Merkel RC Puchala R Wang Z Zeng S Goetsch AL 《Journal of animal science》2009,87(1):400-418
Goat research in the United States has increased but at a rate less than that in production. Research on goat meat includes nutritional quality, packaging, color, sensory characteristics, and preslaughter management. Goat skins have value for leather, but quality of goat leather has not been extensively studied. Research in the production, quality, antibiotic residues, and sensory characteristics of goat milk and its products has aided development of the US dairy goat industry. Limited progress has been made in genetic improvement of milk or meat production. There is need to explore applications of genomics and proteomics and improve consistency in texture and functionality of goat cheeses. New goat meat and milk products are needed to increase demand and meet the diverse tastes of the American public. Despite research progress in control of mohair and cashmere growth, erratic prices and sale of raw materials have contributed to further declines in US production. Innovative and cooperative ventures are needed for profit sharing up to the consumer level. Internal parasites pose the greatest challenge to goat production in humid areas largely because of anthelmintic resistance. Study of alternative controls is required, including immunity enhancement via nutrition, vaccination, pasture management such as co-grazing with cattle, and genetic resistance. Similarly, the importance of health management is increasing related in part to a lack of effective vaccines for many diseases. Nutrition research should address requirements for vitamins and minerals, efficiencies of protein utilization, adjusting energy requirements for nutritional plane, acclimatization, and grazing conditions, feed intake prediction, and management practices for rapid-growth production systems. Moreover, efficient technology transfer methods are needed to disseminate current knowledge and that gained in future research. 相似文献
466.
Ehrlichia chaffeensis, the newly recognized agent of human ehrlichiosis, is closely related to E canis, the causative agent of canine ehrlichiosis. Eight pups were inoculated IV with E chaffeensis-, or with E canis-infected DH82 cells, or organisms released from these host cells. Two additional pups served as nonexposed controls. Marked thrombocytopenia was observed in the E canis-infected pups, but not in those infected with E chaffeensis. Homologous serologic response was observed in the E chaffeensis-exposed pups by postinoculation day (PID) 14 and in the E canis-exposed pups by PID 21. Ehrlichia chaffeensis and E canis were reisolated from the respective inoculated pups on each of 8 attempts from PID 7 to 26. One E chaffeensis-exposed pup that was challenge exposed with E canis via blood transfusion, developed fever, anorexia, and thrombocytopenia, suggesting lack of cross protection against E canis. 相似文献
467.
Nívia Carolina Lopes ROSADO Marcus Rebouas SANTOS Laura Morais Nascimento SILVA Viviane Sisdelli ASSAO Elaine Nery ARAÚJO Natlia Fialho GONZAGA Andressa Fernanda KUNZ Elisabete TAKIUCHI Gustavo Costa BRESSAN Juliana Lopes Rangel FIETTO Abelardo SILVA-JÚNIOR 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2020,82(12):1798
468.
L. E. R. Dawson R. M. Kirkland C. P. Ferris R. W. J. Steen†‡ D. J. Kilpatrick†‡ F. J. Gordon†‡ 《Grass and Forage Science》2002,57(3):255-267
Abstract Two experiments were carried out in consecutive years to examine the influence of cutting date and restricting fermentation by carboxylic acid treatment on the nutrient intake from grass silage by beef cattle. In year 1, four cutting dates during July and August after a primary growth harvest and, in year 2, five cutting dates of primary growth between mid‐May and early July were examined. Herbage was ensiled either untreated or treated with high levels of acid additive (‘Maxgrass’, mean 8·6 l t?1). Ninety‐six (year 1) or forty‐eight (year 2) continental cross steers were used in partially balanced changeover design experiments with each silage type either unsupplemented or supplemented with 4·5 (year 1) or 5·5 (year 2) kg concentrates head?1 d?1. Silage digestibility declined significantly between initial and final harvest dates (P < 0·001), whereas silage dry‐matter (DM) and digestible energy (DE) intakes were significantly higher in the initial compared with final harvest dates in both years of the study (P < 0·01). Similarly, silage DM and DE intakes, and total DM intakes, of acid‐treated and unsupplemented silages were greater than those of untreated and concentrate supplemented silages, respectively (P < 0·001). The results indicate that earlier cutting dates, and addition of acid to herbage before ensiling, can increase silage DM intake by beef cattle. 相似文献