全文获取类型
收费全文 | 1003篇 |
免费 | 44篇 |
专业分类
林业 | 31篇 |
农学 | 19篇 |
基础科学 | 5篇 |
117篇 | |
综合类 | 178篇 |
农作物 | 25篇 |
水产渔业 | 47篇 |
畜牧兽医 | 567篇 |
园艺 | 12篇 |
植物保护 | 46篇 |
出版年
2023年 | 8篇 |
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 18篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 11篇 |
2014年 | 22篇 |
2013年 | 43篇 |
2012年 | 31篇 |
2011年 | 51篇 |
2010年 | 21篇 |
2009年 | 22篇 |
2008年 | 41篇 |
2007年 | 32篇 |
2006年 | 34篇 |
2005年 | 35篇 |
2004年 | 29篇 |
2003年 | 28篇 |
2002年 | 29篇 |
2001年 | 27篇 |
2000年 | 25篇 |
1999年 | 26篇 |
1998年 | 16篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 22篇 |
1991年 | 21篇 |
1990年 | 22篇 |
1989年 | 26篇 |
1988年 | 22篇 |
1987年 | 20篇 |
1986年 | 10篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1979年 | 8篇 |
1977年 | 9篇 |
1974年 | 7篇 |
1972年 | 7篇 |
1971年 | 7篇 |
1969年 | 14篇 |
1967年 | 8篇 |
排序方式: 共有1047条查询结果,搜索用时 15 毫秒
111.
Concerns exist that some uses of antimicrobials in cattle may lead to the emergence, proliferation, dissemination and persistence of resistant pathogenic bacteria in animal agriculture, which in turn can infect humans via the food supply. The degree of perceived risk varies with the clinical indication for which the antimicrobial in question is used. In this study, four uses of antimicrobials are considered, including in acutely sick, chronically sick, at-risk, and high-risk cattle, contrasting the degree of risk among these uses. Using a random sample of 103 feedlot cattle veterinarians and variables drawn from the theory of planned behavior, we predict differences in risk perception by clinical indication with differences in perceived efficacy of antimicrobials, social pressures to use antimicrobials, and moral obligations to use antimicrobials. In most models, veterinarians who perceived that others in the feedlot industry (i.e., other feedlot veterinarians, nutritionists, feedlot clients, and retained owners of cattle) were more likely to expect them to use antimicrobials in one situation versus another, the less likely those veterinarians perceived the risk of antimicrobial risk to be greater in the former versus the latter situation. Only two of these contrasts contained influences outside the immediate feedlot relationships. This exception involves the 'downstream' public: meat packers, retailers, and consumers. Veterinarians who believe that using antimicrobials for acutely sick cattle is more beneficial than using antimicrobials for chronically sick cattle were more likely to believe that antimicrobial resistance was a less probable outcome in acutely sick cattle than in chronically sick cattle. 相似文献
112.
The free-living stages of gastrointestinal nematode parasites of sheep are strongly affected by climate. Thus, extreme heat and cold are detrimental to development and survival, while, within tolerable limits, increasing temperatures generally accelerate development but increase mortality. Moisture is needed for development and translation of larvae from faeces to pasture, and so rainfall is a limiting factor for transmission. Together, these factors underpin seasonal patterns of infection in sheep, as well as geographic variation in the epidemiology and relative importance of different species within Europe. Local knowledge and experience enable treatment to be targeted appropriately to prevent dangerous levels of infection. This traditional know-how can be supplemented by predictive epidemiological models, built on thorough understanding of the influence of climate on larval availability. However, management also has a dominant role in determining patterns of infection, and is itself influenced by climate. Current geographic variation in nematode epidemiology across Europe, and knowledge of systems from outside Europe, can provide only limited perspectives on the likely effects of climate change on disease in future. This is because disease arises from complex interaction between host and parasite factors, and the implementation of optimal control strategies to meet new challenges will be slowed by the inertia of current systems. Approaches to nematode control must therefore take account not only of parasite biology, but also the forces that shape sheep farming systems and management decisions. 相似文献
113.
Cheatgrass (Bromus tectorum L.) is an exotic annual grass causing ecosystem degradation in western US rangelands. We investigated potential mechanisms by which crested wheatgrass (Agropyron cristatum L. Gaertn., Agropyron desertorum [Fisch. {Ex Link} Scult.]) suppresses the growth and invasibility of cheatgrass. Research focused on monthly mineral soil N availability and the proportional concentration of NH4+-N in a crested wheatgrass community by microsite (crested wheatgrass, unvegetated interspace, shrub subcanopy) and soil depth (0–15, 15–30 cm) over a 1-yr period. Mineral soil N in crested wheatgrass microsites ranged from 0.24 to 1.66 mmol · kg-1 and was not appreciably lower than the other microsites or other ecosystems we have measured in the Great Basin. The molar proportion of NH4+-N in the mineral N pool of crested wheatgrass averaged over 85% for the year and is significantly higher than the other microsites and far greater than other plant communities we have measured in the Great Basin. We conclude that crested wheatgrass does not suppress cheatgrass by controlling mineral N below a threshold level; rather, we hypothesize that it may limit nitrification and thereby reduce NO3--N availability to the nitrophile cheatgrass. 相似文献
114.
The future of radiography will be digital. In exotic pet radiography, where some of the animals have a very low body weight and anatomic structures can be small, detail rendition plays an important feature in image quality. Veterinarians should be familiar with the technical principles, image quality criteria, and radiation exposure issues associated with the various types of digital systems currently available. This article discusses basic principles of digital radiography, technical solutions, and selected parameters characterizing detectors, processing, and monitors. An overview of reported experiences is given, and results from experimental clinical studies are reviewed to evaluate the current options and limitations in applying digital radiography to exotic pet medicine. 相似文献
115.
Isabel M. Gamondès Moyano Richard K. Morgan Guillermo Martínez Pastur 《Journal of Sustainable Forestry》2013,32(1):37-59
AbstractThe intensive forest use has caused a significant transformation around the world. Sustainable forest management (SFM) has emerged as an alternative to address concerns regarding resource use, conservation, and socioeconomic benefits. Evidence suggests that its application remains inconsistent. In Argentina, the national government passed a law addressing management aiming to provide guidelines and incentives to steer practices into a sustainable framework. The objectives were: (a) understand what the concept of SFM means to participants in Tierra del Fuego; (b) identify and assess how different factors influence the adoption of SFM; (c) review the stakeholder perceptions on recent regulatory changes; and (d) identify the steps required for improving management. We conducted 52 semi-structured interviews with stakeholders and parties at the national level. New regulatory arrangements were implemented for a short-time before this research was undertaken, and we could not evaluate the success of reform. The study provided deep insight into the policy-making process, and the views held by different stakeholders. The historical mismanagement of the resource, together with an unfavorable past relationship with authorities, has promoted short-term perspectives which resulted in behaviors inconsistent with SFM. Moreover, the characteristic demographic composition brings a social component not identified in the broader literature as relevant for SFM adoption. 相似文献
116.
117.
S. Yoosuk H. B. Ong C. A. Morgan C. T. Whittemore 《Acta Agriculturae Scandinavica, Section A - Animal Sciences》2013,63(4):168-186
Abstract The main goal of this simulator is to predict voluntary feed intake based on the effects of temperature and stocking density. The model indicates the limiting factors relative to diet (protein, energy or ash), housing environmental conditions and stocking density. The concepts of compensatory protein growth, correction of lipid growth, the desired feed intake to meet energy, protein and ash requirements, and influences of stocking density, genotype and sex are also introduced in this model. This study draws a flow chart and steps to predict feed intake of a growing pig to make it clear how the model works. The model simulates the outcomes of feed intake, energy and protein requirements for maintenance, the energy cost for cold thermogenesis, and protein and lipid retention on a daily basis until slaughter weight. This model was also validated by comparison with published experiments. 相似文献
118.
119.
Enzyme-linked immunosorbent assay of ochratoxin A in barley 总被引:3,自引:0,他引:3
M R Morgan R McNerney H W Chan 《Journal of the Association of Official Analytical Chemists》1983,66(6):1481-1484
A noncompetitive, double antibody enzyme-linked immunosorbent assay for ochratoxin A using microtitration plates has been developed and applied to samples of barley. The anti-ochratoxin A antiserum, which is used at high dilution, does not cross-react significantly with ochratoxin B or ochratoxin a. Assay sensitivity for determination of the toxin in barley samples is 60 ng/kg. Minimal sample preparation is required before assay. 相似文献
120.
Wilson DS Teagle DA Alt JC Banerjee NR Umino S Miyashita S Acton GD Anma R Barr SR Belghoul A Carlut J Christie DM Coggon RM Cooper KM Cordier C Crispini L Durand SR Einaudi F Galli L Gao Y Geldmacher J Gilbert LA Hayman NW Herrero-Bervera E Hirano N Holter S Ingle S Jiang S Kalberkamp U Kerneklian M Koepke J Laverne C Vasquez HL Maclennan J Morgan S Neo N Nichols HJ Park SH Reichow MK Sakuyama T Sano T Sandwell R Scheibner B Smith-Duque CE Swift SA Tartarotti P Tikku AA Tominaga M Veloso EA 《Science (New York, N.Y.)》2006,312(5776):1016-1020
Sampling an intact sequence of oceanic crust through lavas, dikes, and gabbros is necessary to advance the understanding of the formation and evolution of crust formed at mid-ocean ridges, but it has been an elusive goal of scientific ocean drilling for decades. Recent drilling in the eastern Pacific Ocean in Hole 1256D reached gabbro within seismic layer 2, 1157 meters into crust formed at a superfast spreading rate. The gabbros are the crystallized melt lenses that formed beneath a mid-ocean ridge. The depth at which gabbro was reached confirms predictions extrapolated from seismic experiments at modern mid-ocean ridges: Melt lenses occur at shallower depths at faster spreading rates. The gabbros intrude metamorphosed sheeted dikes and have compositions similar to the overlying lavas, precluding formation of the cumulate lower oceanic crust from melt lenses so far penetrated by Hole 1256D. 相似文献