全文获取类型
收费全文 | 21459篇 |
免费 | 308篇 |
国内免费 | 11篇 |
专业分类
林业 | 3829篇 |
农学 | 1518篇 |
基础科学 | 185篇 |
3563篇 | |
综合类 | 1190篇 |
农作物 | 2299篇 |
水产渔业 | 2007篇 |
畜牧兽医 | 3666篇 |
园艺 | 1215篇 |
植物保护 | 2306篇 |
出版年
2021年 | 50篇 |
2020年 | 96篇 |
2019年 | 76篇 |
2018年 | 2819篇 |
2017年 | 2790篇 |
2016年 | 1266篇 |
2015年 | 137篇 |
2014年 | 126篇 |
2013年 | 238篇 |
2012年 | 995篇 |
2011年 | 2405篇 |
2010年 | 2290篇 |
2009年 | 1426篇 |
2008年 | 1572篇 |
2007年 | 1785篇 |
2006年 | 249篇 |
2005年 | 322篇 |
2004年 | 300篇 |
2003年 | 336篇 |
2002年 | 282篇 |
2001年 | 147篇 |
2000年 | 164篇 |
1999年 | 109篇 |
1998年 | 57篇 |
1997年 | 40篇 |
1996年 | 45篇 |
1995年 | 43篇 |
1994年 | 54篇 |
1993年 | 66篇 |
1992年 | 93篇 |
1991年 | 79篇 |
1990年 | 85篇 |
1989年 | 79篇 |
1988年 | 52篇 |
1987年 | 64篇 |
1986年 | 49篇 |
1985年 | 61篇 |
1984年 | 63篇 |
1983年 | 54篇 |
1982年 | 56篇 |
1980年 | 36篇 |
1979年 | 40篇 |
1978年 | 46篇 |
1977年 | 50篇 |
1976年 | 43篇 |
1975年 | 34篇 |
1974年 | 41篇 |
1972年 | 35篇 |
1971年 | 34篇 |
1969年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
A CELO-type adenovirus (AV) isolated from fowls with respiratory disease was inoculated experimentally into the tracheas of young birds. No symptoms referable to respiratory infection were evident. Post mortem examination between days 2 and 5 after inoculation revealed pneumonia involving up to 30 per cent of the surface of the lungs. Histologically, a focal to diffuse interstitial lymphocytic infiltration and bronchiolar degeneration were present. Concurrent infections with a mild strain of infectious laryngotracheitis virus (ILT) failed to enhance the pathogenicity of either the AV or ILT infections. 相似文献
14.
Increasing interest in a longer preservation of diluted boar sperm raises questions in the field concerning the choice of the extender. The aim of this study was to evaluate the longevity of boar sperm extended in currently used commercial semen extenders. Three long-term extenders and two short-term extenders were compared for different semen quality parameters that can be assessed under routine laboratory conditions. Sperm morphology, motility, pH and bacteriological contamination were investigated during a 7-day period. The number of dead spermatozoa did not differ significantly among the extenders (p > 0.05). Sperm motility was not only related with storage period but most of all with pH, especially in long-term extenders. Differences between the different extenders were prominent (p < 0.05); the sperm preserved in only one long-term extender showed good motility during the whole test period. In all cases, the pH of the extended semen increased by 0.3-0.5 in the first days of storage and was significantly correlated with a decrease in motility. Bacteriological quality had no significant influence on motility or pH of the semen. In conclusion, we can state that in both short-term extenders and in only one long-term extender, sperm longevity, as evaluated by the parameters used in this study, was sufficient during the preservation period. To preserve the quality of diluted boar semen during long-term storage, the choice of the long-term extender is important. In addition, the monitoring of the pH of extended boar semen in our study emphasizes the importance of the buffering capacity of semen extenders. 相似文献
15.
Eric Lim Teik Chung Michael Predith Frisco Nobilly Anjas Asmara Samsudin Faez Firdaus Abdullah Jesse Teck Chwen Loh 《Tropical animal health and production》2018,50(8):1727-1732
Brachiaria decumbens is an extremely productive tropical grass due to its aggressive growth habit and its adaptation to a varied range of soil types and environments. As a result of the vast availability, treated B. decumbens demonstrates as a promising local material that could be utilised as an improved diet for sheep and goats. Despite the fact that the grass significantly increases weight gains in grazing farm animals, there were many reports of general ill-thrift and sporadic outbreaks of photosensitivity in livestock due to the toxic compound of steroidal saponin found in B. decumbens. Ensiling and haymaking were found to be effective in removing toxin and undesirable compounds in the grass. Biological treatments using urea, activated charcoal, polyethylene glycol, and effective microorganisms were found to be useful in anti-nutritional factor deactivation and improving the nutritive values of feedstuffs. Besides, oral administration of phenobarbitone showed some degree of protection in sheep that fed on B. decumbens pasture. In this review, we aim to determine the effect of B. decumbens toxicity and possible treatment methods on the grass to be used as an improved diet for small ruminant. 相似文献
16.
Daniel A. Truchado Michaël A. J. Moens Sergio Callejas Javier Pérez-Tris Laura Benítez 《Veterinary research communications》2018,42(2):111-120
Papillomaviruses are non-enveloped, DNA viruses that infect skin and mucosa of a wide variety of vertebrates, causing neoplasias or simply persisting asymptomatically. Avian papillomaviruses, with six fully sequenced genomes, are the second most studied group after mammalian papillomaviruses. In this study, we describe the first oral avian papillomavirus, detected in the tongue of a dead Yorkshire canary (Serinus canaria) and in oral swabs of the same bird and other two live canaries from an aviary in Madrid, Spain. Its genome is 8,071 bp and presents the canonical papillomavirus architecture with six early (E6, E7, E1, E9, E2, E4) and two late open reading frames (L1 and L2) and a long control region between L1 and E6. This new avian papillomavirus L1 gene shares a 64% pairwise identity with FcPV1 L1, so it has been classified as a new species (ScPV1) within the Ethapapillomavirus genus. Although the canary died after showing breathing problems, there is no evidence that the papillomavirus caused those symptoms so it could be part of the oral microbiota of the birds. Hence, future investigations are needed to evaluate the clinical relevance of the virus. 相似文献
17.
Leonard Omadang Martin Chamai Emmanuel Othieno Andrew Okwi Francis Olaki Inangolet Francis Ejobi Peter Oba Michael Ocaido 《Tropical animal health and production》2018,50(1):11-17
A cross-sectional study was done from March 2013 to May 2014 to assess knowledge, attitudes, and practices towards cystic echinococcosis (CE) or hydatidosis among selected pastoral and agro-pastoral communities in Uganda. A structured questionnaire was administered to 381 respondents. Multivariate logistic regression analysis was done to find the relationship between knowledge about CE and factors such as age, sex, and level of education across all regions. The odds ratio and confidence interval were used to determine the difference in responses across regions. It was shown that age above 36 years was significantly (p < 0.001) associated with awareness about CE in livestock. Likewise, uneducated (p < 0.0001) and agro-pastoralists (p = 0.01) were significantly less knowledgeable than the educated and pastoralists across all regions. The overall knowledge towards CE in livestock was low 17.8% (95% CI = 14.0–21.6). Dog ownership was high and they never dewormed their freely roaming dogs. Dogs shared water with livestock. In conclusion, knowledge about CE in livestock was low across all regions. Therefore, public health education and formulation of policies towards its control by the relevant stakeholders should be done. Also, the true prevalence of CE in livestock needs to be done so that the magnitude and its public health significance are elucidated. 相似文献
18.
In May 2006, a high intensity wildfire occurred in Songling forest region in Daxing'an Mountains, China. The concentration changes of eight ions (K^+, Na^+, Ca^2+, Mg^2+, Cl^-, Br^-, NO3^- and SO4^2-) were measured in burned and tmbumed streams after fire from May to Oct., 2006. Results show that the most ions flux were higher in burned stream than that in unburned stream during the sampling period, and the greatest concentrations of most ions transported from burned stream occurred in July. After fire, the most amplitude chemical ion was Ca^2+, whose average concentration was 5.50 mg·L^-1 higher than that in unburned stream, and the total concentration of every chemical ion presents a trend Ca^2+〉SO4^2- 〉Na^+〉Mg^2+〉NO3^- . The average concentrations of Ca^2+, SO4^2- , Na^+'Mg^2+,NO3^- showed an increase trend, but those of K^+, Cl^- , Br had a decreased trend. SO4^2- had the largest loss among these anions, followed by NO3^-. Overall, the increase degree of cation was greater than that of anion after burning. 相似文献
19.
W.L. Van Utrecht 《Aquaculture (Amsterdam, Netherlands)》1979,17(2):159-174
Densitometer records were made from the scales of a number of fish species, mainly from pikeperch. Analysis of the records showed that the pattern of hollows, representing the circuli in the curves, was very regular. No arrangement into groups of narrowly interspaced circuli could be demonstrated. It was therefore concluded that the circuli of the surface layer do not produce the “growth-checks”. Ringlike structures were also present in the fibrous basal plate. These were about 3–5 μm closer together than the circuli. These two circular gratings of slightly different inter-ring spacing will create an interference pattern, in this case a circular moiré pattern, having no direct relation to the structures present in the two layers forming the scale. 相似文献
20.
W.H. Van Eck 《Soil biology & biochemistry》1978,10(2):89-92
Lysis of chlamydospores of Fusarium solani f. sp. cucurbitae is enhanced both in chitin and in laminarin amended soils. In soil amended with both chitin and laminarin, lysis of chlamydospores resembles that in control soil. Addition of chitin and laminarin to soil stimulates the growth of both bacteria and actinomycetes. In soils amended with chitin and with both chitin and laminarin, a chitinolytic microflora is stimulated. Penetration of chlamydospore cells by soil microorganisms has not been observed using the electron microscope. The mechanism of lysis of chlamydospores in soil is discussed. 相似文献