全文获取类型
收费全文 | 22536篇 |
免费 | 1125篇 |
国内免费 | 24篇 |
专业分类
林业 | 1301篇 |
农学 | 752篇 |
基础科学 | 173篇 |
3808篇 | |
综合类 | 3369篇 |
农作物 | 1152篇 |
水产渔业 | 1301篇 |
畜牧兽医 | 10142篇 |
园艺 | 363篇 |
植物保护 | 1324篇 |
出版年
2021年 | 246篇 |
2020年 | 270篇 |
2019年 | 317篇 |
2018年 | 407篇 |
2017年 | 486篇 |
2016年 | 390篇 |
2015年 | 287篇 |
2014年 | 455篇 |
2013年 | 921篇 |
2012年 | 806篇 |
2011年 | 1002篇 |
2010年 | 669篇 |
2009年 | 604篇 |
2008年 | 964篇 |
2007年 | 887篇 |
2006年 | 867篇 |
2005年 | 806篇 |
2004年 | 733篇 |
2003年 | 718篇 |
2002年 | 670篇 |
2001年 | 561篇 |
2000年 | 543篇 |
1999年 | 458篇 |
1998年 | 244篇 |
1997年 | 255篇 |
1996年 | 202篇 |
1995年 | 235篇 |
1994年 | 179篇 |
1993年 | 207篇 |
1992年 | 315篇 |
1991年 | 348篇 |
1990年 | 345篇 |
1989年 | 355篇 |
1988年 | 323篇 |
1987年 | 271篇 |
1986年 | 314篇 |
1985年 | 284篇 |
1984年 | 231篇 |
1983年 | 241篇 |
1979年 | 263篇 |
1978年 | 183篇 |
1977年 | 172篇 |
1975年 | 180篇 |
1974年 | 249篇 |
1973年 | 232篇 |
1972年 | 264篇 |
1971年 | 236篇 |
1970年 | 212篇 |
1969年 | 196篇 |
1966年 | 170篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Andresen LO 《The Veterinary record》2005,157(13):376-378
A total of 218 isolates of Staphylococcus hyicus from pigs in eight countries (Belgium, Croatia, Germany, Japan, Korea, Slovenia, the uk and the usa) and 44 isolates from other animals in Belgium, India, Japan and the usa were examined for the genes encoding the exfoliative toxins ExhA, ExhB, ExhC and ExhD by multiplex pcr. The expression of the toxins was confirmed by immunoblot analysis, using monoclonal or polyclonal antibodies specific for each of the toxins. The porcine isolates were from pigs with exudative epidermitis, pigs with other lesions and from healthy pigs, and one or more of the toxins could be found among the isolates from the pigs in all the countries. Toxigenic strains of S hyicus were isolated from both healthy and diseased pigs, but the chance of isolating toxigenic strains from pigs with exudative epidermitis was greater than from pigs with other lesions or healthy pigs. Of the 44 isolates from other animal species, only one isolate, from a hare from Belgium, produced ExhB, and one isolate, from a cow with mastitis from Japan, produced ExhA. 相似文献
102.
Bovine brucellosis in Nigeria 总被引:1,自引:0,他引:1
G O Esuruoso 《The Veterinary record》1974,95(3):54-58
103.
Peter M. Kiffney Ben Cram Paul L. Faulds Karl Burton Michele Koehler Thomas P. Quinn 《Ecology of Freshwater Fish》2018,27(4):1037-1053
To examine the role of longitudinal connectivity on the spatial and temporal dynamics of mountain whitefish (Prosopium williamsoni), we quantified movement and population dynamics following installation of the Landsburg Dam fishway, Cedar River, WA, USA. Mountain whitefish is widely distributed, poorly studied and not the focus of restoration. Before the fishway, mountain whitefish were not observed above the dam. Here, we focus on snorkel counts collected at reach and mesohabitat (e.g. pools) scales over 11 summers on the 20‐km above‐dam segment following restoration. A camera within the ladder provided number, size and movement timing, thereby informing on behaviour and recolonisation. Segment‐scale abundance increased following fish passage reaching an asymptote in 7 years, and mountain whitefish were detected throughout the main stem in 10 years. Annual movement through the ladder increased over time and was positively correlated with instream abundance and discharge, but negatively correlated with water temperature. About 60% of fish movements occurred in spring and early summer, potentially for foraging opportunities. Reach‐scale abundance peaked between 7 and 10 km from the dam; deep, cool (~10.6 to 11.6°C) conditions characterised these reaches. At the mesohabitat scale, mountain whitefish detection increased with depth and velocity after accounting for distance from the dam. Our results show how restoring longitudinal connectivity allowed this nontarget species to colonise newly available habitat. Their response supports the critical roles of longitudinal connectivity and environmental conditions, that manifest at different spatial scales, in dictating how freshwater fish respond to habitat disturbance. 相似文献
104.
A 6-year study was conducted in 4 dairy herds in Iowa in which Johne's disease was diagnosed previously. Fecal specimens were collected at 6-month intervals from animals 2 years of age and over for mycobacteriologic examination. Serum samples were obtained at 3-month intervals and tested by enzyme-linked immunosorbent assay (ELISA). The antigen used in the ELISA was a potassium chloride extract of a field strain of Mycobacterium paratuberculosis. The ELISA reactions were observed in 87% of the cows from which M. paratuberculosis was isolated. Dairy producers that participated in the Johne's control program reported reduced economic losses. Increased income was attributed to improved milk production, increased value of vaccinated animals sold as replacements to other dairy herds in which Johne's disease had been diagnosed, and the increased market value of slaughter animals removed from the herd. 相似文献
105.
106.
107.
Poxvirus infections are common in domestic birds in Germany, but they are rare in birds of prey. Only species of falconidae imported from Arabian or Asian countries have so far tested positive for poxvirus, and, among these, only raptors kept for falconry. As part of a reintroduction programme in the northern county of Mecklenburg-Western Pomerania, which is adjacent to the Baltic Sea, 21 young peregrine falcons were released into the wild; six of them died and one was examined postmortem, its tissues being examined by light and electron microscopy. In addition, an ELISA for fowlpox, pigeonpox and canarypox was applied. No virus could be isolated and propagation in culture failed, but virus particles were detected by electron microscopy in lesions from its skin and tongue. 相似文献
108.
Russo V. Martelli M. Mauro A. Di Giacinto O. Nardinocchi D. Berardinelli P. 《Veterinary research communications》2007,31(1):201-204
Veterinary Research Communications - Russo, V., Martelli, M., Mauro, A., Di Giacinto, O., Nardinocchi, D. and Berardinelli, P., 2007. Nuclear remodelling in growing oocytes of sheep. Veterinary... 相似文献
109.
M. Angeles Achon Vicente Medina Michael Shanks Peter Markham George P. Lomonossoff 《European journal of plant pathology / European Foundation for Plant Pathology》1994,100(2):157-165
In order to characterise and classify an unknown maize-infecting potyvirus isolated from fields in northeast Spain, the entire coat protein gene and the C-terminal twothirds of the large nuclear inclusion protein (NIb) gene were cloned and sequenced. Protein sequencing enabled the cleavage site between the two proteins to be deduced and also revealed that on storage the viral coat protein undergoes a specific degradation in which the N-terminal 39 amino acids are removed. Comparison of the nucleotide sequence of the 3 non-coding region of the viral RNA and the predicted amino acid sequence of the coat protein with the equivalent regions of other members of the potyvirus group revealed that the Spanish virus is closely related to maize dwarf mosaic virus strain A. 相似文献
110.
de la Fuente J Ruybal P Mtshali MS Naranjo V Shuqing L Mangold AJ Rodríguez SD Jiménez R Vicente J Moretta R Torina A Almazán C Mbati PM de Echaide ST Farber M Rosario-Cruz R Gortazar C Kocan KM 《Veterinary microbiology》2007,119(2-4):382-390
Anaplasma marginale is a tick-borne pathogen of cattle that causes the disease bovine anaplasmosis worldwide. Major surface proteins (MSPs) are involved in host-pathogen and tick-pathogen interactions and have been used as markers for the genetic characterization of A. marginale strains and phylogenetic studies. MSP1a is involved in the adhesion and transmission of A. marginale by ticks and varies among geographic strains in the number and sequence of amino-terminal tandem repeats. The aim of this study was to characterize the genetic diversity of A. marginale strains collected from countries in North and South America, Europe, Asia, Africa and Australia, inclusive of all continents. In this study, we characterized 131 strains of A. marginale using 79 MSP1a repeat sequences. These results corroborated the genetic heterogeneity of A. marginale strains in endemic regions worldwide. The phylogenetic analyses of MSP1a repeat sequences did not result in clusters according to the geographic origin of A. marginale strains but provided phylogeographic information. Seventy-eight percent of the MSP1a repeat sequences were present in strains from a single geographic region. Strong (> or =80%) support was found for clusters containing sequences from Italian, Spanish, Chinese, Argentinean and South American strains. The phylogenetic analyses of MSP1a repeat sequences suggested tick-pathogen co-evolution and provided evidence of multiple introductions of A. marginale strains from various geographic locations worldwide. These results contribute to the understanding of the genetic diversity and evolution of A. marginale and tick-pathogen interactions. 相似文献