全文获取类型
收费全文 | 87766篇 |
免费 | 5268篇 |
国内免费 | 42篇 |
专业分类
林业 | 2993篇 |
农学 | 2730篇 |
基础科学 | 529篇 |
9965篇 | |
综合类 | 16287篇 |
农作物 | 3672篇 |
水产渔业 | 4333篇 |
畜牧兽医 | 45844篇 |
园艺 | 1086篇 |
植物保护 | 5637篇 |
出版年
2019年 | 817篇 |
2018年 | 1200篇 |
2017年 | 1381篇 |
2016年 | 1296篇 |
2015年 | 1152篇 |
2014年 | 1365篇 |
2013年 | 3477篇 |
2012年 | 2569篇 |
2011年 | 3058篇 |
2010年 | 1997篇 |
2009年 | 1964篇 |
2008年 | 2947篇 |
2007年 | 2861篇 |
2006年 | 2718篇 |
2005年 | 2563篇 |
2004年 | 2400篇 |
2003年 | 2430篇 |
2002年 | 2292篇 |
2001年 | 2919篇 |
2000年 | 2793篇 |
1999年 | 2278篇 |
1998年 | 985篇 |
1997年 | 901篇 |
1996年 | 796篇 |
1995年 | 966篇 |
1994年 | 867篇 |
1993年 | 860篇 |
1992年 | 1821篇 |
1991年 | 1818篇 |
1990年 | 1761篇 |
1989年 | 1823篇 |
1988年 | 1579篇 |
1987年 | 1686篇 |
1986年 | 1744篇 |
1985年 | 1676篇 |
1984年 | 1314篇 |
1983年 | 1172篇 |
1982年 | 844篇 |
1981年 | 724篇 |
1979年 | 1114篇 |
1978年 | 904篇 |
1977年 | 790篇 |
1976年 | 740篇 |
1975年 | 811篇 |
1974年 | 1002篇 |
1973年 | 1046篇 |
1972年 | 997篇 |
1971年 | 954篇 |
1970年 | 889篇 |
1969年 | 815篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
利用“Y”型选择器和草地寄主搜寻试验,就春臀钩土蜂两个品系和日本丽金龟瞥钩土蜂对日本金龟子的搜索能力进行了比较。结果表明,两种土蜂的3个品系对日本金龟子3龄幼虫的存在与否没有表现出明显的辨别能力。虫粪对土蜂搜索寄主有一定的引导作用,但日本丽金龟臀钩土蜂的趋性没有春臀钩土蜂明显。寄主虫体气味与虫粪混合存在比只有虫粪存在更能吸引土蜂。土蜂可以在相隔两个侧臂20cm的距离内感知金龟子幼虫的存在;当寄主与非寄主金龟子同时存在时,不能辨别出寄主;但能通过虫粪辨认寄主所在方向。春臀钩土蜂两个品系对日本金龟子幼虫气味表现出极强的趋性。日本丽金龟臀钩土蜂则受非寄主幼虫气味干扰。草地寄主搜寻试验表明,春臀钩土蜂CH—SD品系仅搜索内开口隧道内幼虫;A—NC品系对隧道的开口没有表现出特殊的选择性。67.5%雌蜂能够感知寄主幼虫的存在并自行挖洞搜索。寄主粪便可以引导土蜂从人工隧道开口进入。网罩内草地上的虫粪可以干扰土蜂对地下寄主位置的判断。 相似文献
993.
C. H. A. Snijders 《European journal of plant pathology / European Foundation for Plant Pathology》1990,96(4):187-198
Summary An infection of bread wheat by fusarium head blight contaminates the crop with mycotoxins, particularly deoxynivalenol (DON) and nivalenol (NIV). The toxicity and natural occurrence of these mycotoxins in wheat are reviewed. Based on 8 years data of fusarium head blight epidemics of wheat in the Netherlands, DON contamination of the grain was estimated. Fusarium head blight ratings averaged an infection of 1.7% of all spikelets; estimates for DON contamination averaged 0.9 mg kg–1. Taking a guideline level for DON in uncleaned bread wheat of 2 mg kg–1, in 1979 and 1982 a wheat crop was produced with estimated DON concentrations above the limit of tolerance. Human and animal exposure to mycotoxins in the Netherlands appears to be small but chronic. The information presented in this paper illustrates the need for an annual evaluation of the crop for fusarium head blight incidence and mycotoxin content, and the necessity of fusarium head blight resistant wheat cultivars.Samenvatting Aaraantasting van tarwe doorFusarium culmorum enFusarium graminearum leidt tot vorming van mycotoxinen in het graan, waarvan deoxynivalenol (DON) en nivalenol (NIV) de belangrijkste toxinen zijn. In dit artikel wordt een overzicht gegeven van de toxicologische aspecten, en het voorkomen van deze toxinen in tarwe. Informatie over DON en NIV in tarwe in West-Europa is schaars. Gebaseerd op gegevens vanFusarium epidemieën in de jaren 1979–1986 wordt een schatting gegeven van de concentratie DON in Nederlandse tarwe. Rekening houdend met de herkomst en verwerking van tarwe, blijken zowel in dierlijk als menselijk voedsel lage concentraties DON chronisch voor te komen. Op basis van een maximaal toelaatbare dagelijkse dosis DON van 3 g kg–1 lichaamsgewicht is de schatting van de dagelijkse opname van DON in het jaar volgend op de oogst van 1982 net op de grens. Zowel een jaarlijkse inventarisatie vanFusarium aantasting en DON besmetting van het graan, als de ontwikkeling vanFusarium-resistente rassen zijn noodzakelijk. 相似文献
994.
Aggressiveness and other factors relating to displacement of populations of Phytophthora infestans in England and Wales 总被引:5,自引:0,他引:5
J.P. Day R.C. Shattock 《European journal of plant pathology / European Foundation for Plant Pathology》1997,103(4):379-391
Mating type, in vitro sensitivity to the phenylamide fungicide metalaxyl, and mitochondrial (mtDNA) haplotype were determined in some or all of 618 isolates of Phytophthora infestans from the years between 1978 and 1995. A2 mating type occurred infrequently in most but not all years and insensitivity to metalaxyl increased over time. After 1982, the mtDNA Ib haplotype was largely replaced (except for one isolate in 1986 and one in 1995) by two new haplotypes, Ia and IIa. Type Ia was much more common than type IIa.Approximately one quarter of these isolates (165) were compared using two components of fitness associated with aggressiveness (infection frequency × number of sporangia per lesion) on detached leaves of cultivars Maris Piper, Cara and Stirling, which were chosen as exhibiting increasing levels of race non-specific resistance. Isolates were compared with three standard isolates of low, intermediate or high aggressiveness, and the data standardised for comparison between experiments. On cvs. Cara and Stirling, but not on Maris Piper, mtDNA Ia and IIa haplotypes were more aggressive than type Ib in several separate experiments. Similarly, metalaxyl sensitive phenotypes were more aggressive than insensitive phenotypes on Cara and Stirling but not on Maris Piper. The displacement of mtDNA type Ib by types Ia and IIa over this period may have been a result of the lower aggressiveness and lack of complete insensitivity to metalaxyl in type Ib isolates. 相似文献
995.
Eckhard Koch Annegret Schmitt Dietrich Stephan Carola Kromphardt Marga Jahn Hermann-Josef Krauthausen Gustaf Forsberg Sigrid Werner Tahsein Amein Sandra A. I. Wright Federico Tinivella Maria L. Gullino Steven J. Roberts Jan van der Wolf Steven P. C. Groot 《European journal of plant pathology / European Foundation for Plant Pathology》2010,127(1):99-112
The current study was initiated to evaluate the efficacy of physical methods (hot water, aerated steam, electron treatment) and agents of natural origin (resistance inducers, plant derived products, micro-organisms) as seed treatments of carrots for control of Alternaria dauci and A. radicina. Control of both Alternaria species by seed treatment with the resistance inducers was generally poor. Results were also not satisfactory with most of the formulated commercial micro-organism preparations. Based on the average of five field trials, one of these, BA 2552 (Pseudomonas chlororaphis), provided a low but significant increase in plant stand. Among the experimental micro-organisms, the best results were obtained with Pseudomonas sp. strain MF 416 and Clonostachys rosea strain IK726. A similar level of efficacy was provided by seed treatment with an emulsion (1%) of thyme oil in water. Good and consistent control was generally achieved with the physical methods aerated steam, hot water and electron treatment. Aerated steam treatment was, apart from the thiram-containing chemical standard, the best single treatment, and its performance may at least partially be due to extensive pre-testing, resulting in dosages optimally adapted to the respective seed lot. In some of the experiments the effect of the hot water treatment, which was tested at a fixed, not specifically adapted dosage, was significantly improved when combined with a Pseudomonas sp. MF 416 or C. rosea IK726 treatment. The results are discussed in relation to the outcome of experiments in which the same seed treatment methods and agents were tested in other seed-borne vegetable pathosystems. 相似文献
996.
BACKGROUND: In pest management research, harmonic radar systems have been largely used to study insect movement across open or vegetation‐poor areas because the microwave signal is attenuated by the high water content of vegetation. This study evaluated whether the efficacy of this technology is sufficient to track insects in vegetative landscapes. RESULTS: Field efficacy data were collected using portable harmonic microwave radar and electronic dipole tags mounted on adults of three economically important pests: Leptinotarsa decemlineata (Say), Diabrotica virginifera virginifera (LeComte) and Conotrachelus nenuphar Herbst. Detection and recovery of tagged Colorado potato beetles, plum curculios and western corn rootworms was high within and among potato plants, moderate within apple trees and high within, but not between, corn plants respectively. The efficacy of the radar depends on the ability of the operator to move around the host, scanning for a signal ‘sightline’ with the tagged insect among plant structures. CONCLUSION: The detection rate of tagged insects by harmonic radar systems is high enough to track the walking path of pests through low row crops such as potato, tall row crops such as corn or tall but well‐separated trees of orchard‐type crops by adapting the scanning procedure to the vegetative architecture. Copyright © 2010 Crown in the right of Canada. Published by JohnWiley & Sons, Ltd 相似文献
997.
Menzies-Gow NJ Katz LM Barker KJ Elliott J De Brauwere MN Jarvis N Marr CM Pfeiffer DU 《The Veterinary record》2010,167(18):690-694
A retrospective study of laminitis was carried out to identify risk factors associated with this disease on an East Anglian farm with approximately 1000 animals living in an area of 1000 acres. Medical records between January 1997 and May 2000 and between April 2005 and March 2008 were reviewed, and the age, sex, weight (kg), height (inches [in] and hands [H]) and weight-to-height ratio (kg/in) was recorded. The prevalence, incidence and seasonality of laminitis were determined and their relationship to the monthly temperature, rainfall and hours of sunshine was evaluated. Averaged over the six years, the highest prevalence (2.6 per cent) and incidence (16 cases/1000 animals) of laminitis occurred in May. The findings of a multivariate analysis revealed that females (P=0.007, odds ratio [OR] 1.46, 95 per cent confidence interval [CI] 1.1053 to 1.9646) and light animals (P ≤ 0.001, OR=0.995, 95 per cent CI =0.9932 to 0.9963) had the greatest risk of developing laminitis. A positive association was found between hours of sunshine and incidence (P=0.007, relative risk [RR] 1.009, 95 per cent CI 1.001 to 1.012) and prevalence (P=0.002, RR 1.008, 95 per cent CI 1.003 to 1.012) of laminitis. The data suggest that there is a relationship between season, sex of the animal and the development of laminitis. 相似文献
998.
Cannas da Silva J Noordhuizen JP Vagneur M Bexiga R Gelfert CC Baumgartner W 《The Veterinary quarterly》2006,28(1):23-32
The nature of veterinary work in dairy health management in Europe has changed over the past years and will change even more dramatically in the near future. The consumers and the media show increasing concern about animal welfare, safety of products of animal origin and traceability of animal products. Farmers in Europe have to produce under strict, often expensive and laborious regulations, while still commercially competing with farmers outside the EU and not subject to the same rules. Veterinarians should adapt their knowledge and skills to the new challenges and developments of the dairy sector. Dairy farmers nowadays ask for support in areas that go beyond clinical activities: environmental protection, welfare, nutrition, grassland management, economics and business management. Bovine practitioners should be able to advise in many different areas and subjects--that is the challenge to our profession. Veterinary education with regards to cattle health management should start with individual animal clinical work, which constitutes the basis of herd health advisory programmes. The bovine practitioner should then look beyond that and regard the herd as the unit. Each diseased cow or group of cows should be detected early enough to avoid financial losses or such losses should be prevented altogether by detecting and managing risk factors contributing to disease occurrence. Herd health and production management programmes represent the first level to optimise dairy farm performance. Expansions to that should further be considered, comprising both animal health and welfare issues, as well as food safety and public health issues. The latter could be addressed by quality risk management programmes following the HACCP-principles. Cattle veterinarians should follow recent developments and invest in new skills and knowledge in order to maintain their usefulness to the modern dairy farmer. Finally we are convinced that the cattle practitioner should evolve into this direction, otherwise the veterinarian as we know him will miss the train in the next years. 相似文献
999.
A Multistate Investigation of Antibiotic‐Resistant Salmonella enterica Serotype I 4,[5],12:i:‐ Infections as Part of an International Outbreak Associated with Frozen Feeder Rodents
下载免费PDF全文
![点击此处可从《Zoonoses and public health》网站下载免费的PDF全文](/ch/ext_images/free.gif)
E. J. Cartwright T. Nguyen C. Melluso T. Ayers C. Lane A. Hodges X. Li J. Quammen S. J. Yendell J. Adams J. Mitchell R. Rickert R. Klos I. T. Williams C. Barton Behravesh J. Wright 《Zoonoses and public health》2016,63(1):62-71
While most human Salmonella infections result from exposure to contaminated foods, an estimated 11% of all Salmonella infections are attributed to animal exposures, including both direct animal handling and indirect exposures such as cleaning cages and handling contaminated pet food. This report describes the epidemiologic, environmental and laboratory investigations conducted in the United States as part of the response to an international outbreak of tetracycline‐resistant Salmonella enterica serotype I 4,[5],12:i:‐ infections with over 500 illnesses occurring from 2008 to 2010. This investigation found that illness due to the outbreak strain was significantly associated with exposure to pet reptiles and frozen feeder rodents used as food for pet reptiles. Salmonella isolates indistinguishable from the outbreak strain were isolated from a frozen feeder mice‐fed reptile owned by a case patient, as well as from frozen feeder mice and environmental samples collected from a rodent producing facility (Company A). An international voluntary recall of all Company A produced frozen feeder animals sold between May 2009 and July 2010 occurred. Only 13% of cases in our investigation were aware of the association between Salmonella infection and mice or rats. Consumers, the pet industry, healthcare providers and veterinarians need to be aware of the potential health risk posed by feeder rodents, whether live or frozen. Frozen feeder rodent producers, suppliers and distributors should follow the animal food labelling requirements as described in 21 CFR §501.5, and all packages of frozen feeder rodents should include safe handling instructions. Persons should wash their hands thoroughly with soap and water after handling live or frozen feeder rodents, as well as reptiles or anything in the area where the animals live. Continued opportunities exist for public health officials, the pet industry, veterinarians and consumers to work together to prevent salmonellosis associated with pet food, pets and other animals. 相似文献
1000.
Oidtmann BC Crane CN Thrush MA Hill BJ Peeler EJ 《Preventive veterinary medicine》2011,102(4):329-340
A semi-quantitative model is presented to rank freshwater rainbow trout farms within a country or region with regards to the risk of becoming infected and spreading a specified pathogen. The model was developed to support a risk-based surveillance scheme for notifiable salmonid pathogens. Routes of pathogen introduction and spread were identified through a process of expert consultation in a series of workshops. The routes were combined into themes (e.g. exposure via water, mechanical transmission). Themes were weighted based on expert opinion. Risk factors for each route were scored and combined into a theme score which was adjusted by the weight. The number of sources and consignments were used to assess introduction via live fish movements onto the farm. Biosecurity measures were scored to assess introduction on fomites. Upstream farms, wild fish and processing plants were included in assessing the likelihood of introduction by water. The scores for each theme were combined to give separate risk scores for introduction and spread. A matrix was used to combine these to give an overall risk score. A case study for viral haemorrhagic septicaemia is presented. Nine farms that represent a range of farming practices of rainbow trout farms in England and Wales are used as worked examples of the model. The model is suited to risk rank freshwater salmonid farms which are declared free of the pathogen(s) under consideration. The score allocated to a farm does not equate to a quantitative probability estimate of the farm to become infected or spread infection. Nevertheless, the method provides a transparent approach to ranking farms with regards to pathogen transmission risks. The output of the model at a regional or national level allows the allocation of surveillance effort to be risk based. It also provides fish farms with information on how they can reduce their risk score by improving biosecurity. The framework of the model can be applied to different production systems which may have other routes of disease spread. Further work is recommended to validate the allocated scores. Expert opinion was obtained through workshops, where the outputs from groups were single point estimates for relative weights of risks. More formal expert opinion elicitation methods could be used to capture variation in the experts' estimates and uncertainty and would provide data on which to simulate the model stochastically. The model can be downloaded (in Microsoft(?)-Excel format) from the Internet at: http://www.cefas.defra.gov.uk/6701.aspx. 相似文献