全文获取类型
收费全文 | 5885篇 |
免费 | 296篇 |
国内免费 | 5篇 |
专业分类
林业 | 463篇 |
农学 | 192篇 |
基础科学 | 39篇 |
1187篇 | |
综合类 | 905篇 |
农作物 | 230篇 |
水产渔业 | 367篇 |
畜牧兽医 | 2185篇 |
园艺 | 186篇 |
植物保护 | 432篇 |
出版年
2023年 | 39篇 |
2022年 | 41篇 |
2021年 | 101篇 |
2020年 | 155篇 |
2019年 | 142篇 |
2018年 | 156篇 |
2017年 | 141篇 |
2016年 | 145篇 |
2015年 | 129篇 |
2014年 | 158篇 |
2013年 | 284篇 |
2012年 | 336篇 |
2011年 | 431篇 |
2010年 | 244篇 |
2009年 | 185篇 |
2008年 | 335篇 |
2007年 | 339篇 |
2006年 | 302篇 |
2005年 | 307篇 |
2004年 | 279篇 |
2003年 | 280篇 |
2002年 | 265篇 |
2001年 | 66篇 |
2000年 | 73篇 |
1999年 | 85篇 |
1998年 | 57篇 |
1997年 | 53篇 |
1996年 | 54篇 |
1995年 | 39篇 |
1994年 | 48篇 |
1993年 | 49篇 |
1992年 | 39篇 |
1991年 | 47篇 |
1990年 | 46篇 |
1989年 | 42篇 |
1988年 | 39篇 |
1987年 | 39篇 |
1986年 | 54篇 |
1985年 | 32篇 |
1984年 | 44篇 |
1983年 | 35篇 |
1982年 | 36篇 |
1981年 | 27篇 |
1980年 | 20篇 |
1979年 | 23篇 |
1978年 | 27篇 |
1977年 | 26篇 |
1975年 | 20篇 |
1973年 | 24篇 |
1972年 | 21篇 |
排序方式: 共有6186条查询结果,搜索用时 557 毫秒
31.
K Christiana Grim Thomas McCutchan Jun Li Margery Sullivan Thaddeus K Graczyk Glenn McConkey Michael Cranfield 《Journal of zoo and wildlife medicine》2004,35(2):154-161
Captive juvenile African black-footed penguins (Spheniscus demersus) housed in an outdoor enclosure at the Baltimore Zoo have an average 50% mortality from avian malarial (Plasmodium sp.) infection each year without intense monitoring for disease and chemotherapeutic intervention. During the 1996 malaria transmission season, the safety and efficacy of an anti-circumsporozoite (CSP) DNA vaccine encoding the Plasmodium gallinaceum CSP protein against P. relictum were studied. The goal was to reduce clinical disease and death without initiating sterile immunity after release into an area with stable, endemic avian malaria. The birds were monitored for adverse clinical signs associated with vaccination, the stimulation of an anti-CSP antibody response, and protection afforded by the vaccine. The presence of P. relictum in trapped culicine mosquitoes within the penguin enclosure was monitored to assess parasite pressure. Among the vaccinated penguins, the parasitemia rate dropped from approximately 50% to approximately 17% despite intense parasite pressure, as determined by mosquito infection rate. During the year of the vaccine trial, no mortalities due to malaria occurred and no undesirable vaccination side effects occurred. This is the first trial of an antimalarial vaccine in a captive penguin colony. 相似文献
32.
Thomas J Inzana Gretchen E Glindemann Gerald Snider Susan Gardner Lisa Crofton Barbara Byrne Joseph Harper 《Journal of veterinary diagnostic investigation》2004,16(5):374-381
Francisella tularensis type A is the primary cause of tularemia in animals and humans in North America. The majority of research on F. tularensis has been done with the attenuated live vaccine strain (LVS), which is a type B, but very few wild-type F. tularensis strains have been characterized. A gram-negative coccobacillus that was isolated in pure culture from the lungs of a cat that died after being lost for 5 days was received for identification at the Virginia-Maryland Regional College of Veterinary Medicine Teaching hospital. The isolate (strain TI0902) was not identified (or was misidentified) by commercial identification systems; however, it was identified as F. tularensis subspecies tularensis (type A) by sequencing a portion of the 16S ribosomal RNA gene. Furthermore, repetitive extragenic palindromic sequences-polymerase chain reaction amplified a 4-kb DNA fragment from TI0902 that was characteristic of F. tularensis type A but not type B. The electrophoretic profile of the lipopolysaccharide of strain TI0902 was identical to that of the LVS by Western blotting with antiserum to LVS. The protein-enriched outer membrane of strain TI0902 contained 6-8 proteins, which were similar in molecular size to those from the LVS. Electron microscopy of negatively stained and alcian blue-stained LVS and TI0902 cells showed that both strains were coccobacillary in shape and may be encapsulated. However, after mouse challenge, the TI0902 strain was clearly more virulent than the LVS strain. Results of this study indicate that the genotype and phenotype of wild-type F. tularensis type A strain TI0902 is similar, but not identical, to that of the LVS strain. Further studies will help determine whether pathogenesis and host-pathogen interactions are also similar between the 2 strains. 相似文献
33.
Kathryn C Gamble Michael M Garner Laura Krause Thomas P Alvarado 《Journal of zoo and wildlife medicine》2004,35(3):361-369
Two adult female rock hyraxes (Procavia capensis) at the Dallas Zoo were confirmed with spontaneous diabetes mellitus from 1997-2000, whereas a third animal with a similar clinical presentation never became hyperglycemic. The pancreas in all three animals showed pancreatic islet fibrosis (PIF). Retrospective examination of medical records for rock hyraxes acquired by this collection or born into it from 1991-2002 identified eight more animals affected with PIE All affected animals, including three males and eight females, were 1-7 yr of age and presented either with vague clinical signs of soft feces and rough hair coat or were acutely moribund or dead. Clinical pathology data was available for seven of the animals before onset of overt clinical signs and revealed inappropriate hyperglycemia in six, as well as elevated serum concentrations of creatine phosphokinase, amylase, and lipase in all seven animals. Pedigree evaluation did not support a familial pattern for PIE Review of the histopathology findings from nine other zoologic collections with rock hyrax deaths during the study period identified six institutions with 12 additional cases genetically unrelated to the incident collection. Histopathology and viral serology did not support an infectious cause. Analysis of serum anti-islet and anti-insulin antibodies did not suggest autoimmune disease, and none of the animals had known exposure to toxic substances. Limited nutritional analyses did not support a nutritional basis for the condition, and the cause for PIF remains unknown. 相似文献
34.
Thomas Miedaner Angela G. Schilling Geiger 《European journal of plant pathology / European Foundation for Plant Pathology》2004,110(1):63-70
Fusarium culmorum is a phytopathogenic, toxigenic fungus causing seedling diseases, foot rot and head blight of cereals. For estimating competition effects in mixtures of two single-spore isolates, two winter rye single crosses were tested with either four isolates individually or four 1 : 1 mixtures of the same isolates in six field environments. Two isolates (FC46, FC64) were highly aggressive deoxynivalenol (DON) and 3-acetyl DON-producers, the other two (FC30, FC71) were medium aggressive nivalenol-producers. Rye heads were inoculated during flowering with conidia of pairs of isolates expressing similar (FC46 + FC64, FC30 + FC71) or contrary (FC46 + FC71, FC30 + FC64) levels of aggressiveness and similar or different concentrations and chemotypes of mycotoxins, respectively. Head blight rating and yield components relative to the non-inoculated plots were recorded as aggressiveness traits. Additionally, mycotoxin concentrations were measured in the rye grain. Random pathogen samples were re-isolated from heads at the onset of symptom development and analysed by molecular markers (RAPD–PCR) in one environment. Aggressiveness of the isolate mixtures was significantly lower than that of the isolates applied individually on both rye genotypes. Similarly, mycotoxin concentrations were significantly lower in the mixtures in seven out of eleven comparisons. Among the re-isolates, the component genotypes of a mixture significantly deviated from the inoculated 1 : 1 ratio when a particular isolate (FC46) was present in the mixture. This isolate displayed a superior competitive ability irrespective of the aggressiveness or mycotoxin profile of the mixing partner illustrating that pathogenic fitness is caused by additional factors that have not, as yet, been identified. 相似文献
35.
Fractional excretion of electrolytes in volume‐responsive and intrinsic acute kidney injury in dogs: Diagnostic and prognostic implications 下载免费PDF全文
36.
37.
Pedro Martínez-Gómez Angela S. Prudencio Thomas M. Gradziel Federico Dicenta 《Euphytica》2017,213(8):197
Regulation of flowering time in almond, as in other Prunus species, is a complex process involving both chill and heat requirements. Following exposure to appropriate consecutive periods of cold and warm temperatures, the buds break dormancy and sprout or flower depending on bud type. To maximize flowering and subsequent vegetative growth and fruit set, chilling and ensuing warm temperature requirements have to be fully satisfied. Because of its potential for very early flowering, flowering time in almond is a major determinant of its adaptation to new environments. In colder regions, Late-flowering is often necessary to avoid frost damage during and just after flowering. Consequently, the selection of delayed flowering times remains an important objective in almond improvement programs. Flowering time is considered a quantitative though highly heritable trait. In addition, a dominant gene (Late flowering, Lb), originally identified in a spontaneous mutation of the Californian almond cultivar ‘Nonpareil’, was also described. The objective of this review is a comparative analysis of the effects of regional adaptation, breeding and mutation on the delay of flowering time in new almond cultivars. Findings indicate that the adaptation of almonds from the Mediterranean basin to colder regions in Northern Europe and America has been mainly achieved through delayed flowering. These adapted late-flowering cultivars have usually been developed by selecting desired quantitative genes within each regional germplasm. Additional progress thus appears achievable with a more comprehensive understanding of the quantitative and qualitative genetics controlling this trait. The use of molecular markers for the early selection of genes conferring late flowering, including both spontaneous mutations as well as unique regional germplasm, should allow development of even later cultivars including ultra-late cultivars flowering as into April. 相似文献
38.
39.
40.
Monica L. Bond Curtis M. Bradley Christian Kiffner Thomas A. Morrison Derek E. Lee 《Landscape Ecology》2017,32(8):1705-1721