全文获取类型
收费全文 | 1613篇 |
免费 | 149篇 |
国内免费 | 2篇 |
专业分类
林业 | 46篇 |
农学 | 15篇 |
基础科学 | 33篇 |
168篇 | |
综合类 | 321篇 |
农作物 | 62篇 |
水产渔业 | 140篇 |
畜牧兽医 | 918篇 |
园艺 | 18篇 |
植物保护 | 43篇 |
出版年
2021年 | 21篇 |
2020年 | 25篇 |
2019年 | 31篇 |
2018年 | 30篇 |
2017年 | 31篇 |
2016年 | 19篇 |
2015年 | 29篇 |
2014年 | 35篇 |
2013年 | 88篇 |
2012年 | 44篇 |
2011年 | 74篇 |
2010年 | 38篇 |
2009年 | 46篇 |
2008年 | 66篇 |
2007年 | 64篇 |
2006年 | 46篇 |
2005年 | 56篇 |
2004年 | 43篇 |
2003年 | 56篇 |
2002年 | 38篇 |
2001年 | 38篇 |
2000年 | 38篇 |
1999年 | 30篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1993年 | 14篇 |
1992年 | 29篇 |
1991年 | 37篇 |
1990年 | 28篇 |
1989年 | 35篇 |
1988年 | 44篇 |
1987年 | 31篇 |
1986年 | 31篇 |
1985年 | 38篇 |
1984年 | 27篇 |
1983年 | 29篇 |
1982年 | 13篇 |
1979年 | 19篇 |
1978年 | 15篇 |
1976年 | 11篇 |
1975年 | 14篇 |
1974年 | 23篇 |
1973年 | 15篇 |
1972年 | 11篇 |
1971年 | 12篇 |
1970年 | 16篇 |
1968年 | 10篇 |
1967年 | 10篇 |
排序方式: 共有1764条查询结果,搜索用时 0 毫秒
51.
52.
53.
54.
The concentrations of basophils in blood and bone marrow were monitored in guinea pigs subjected to primary and secondary infestations with larvae of Dermacentor andersoni. In these guinea pigs a significant increase of basophils was evident in peripheral blood. The response following the secondary infestation was more rapid and more intense than that following the primary infestation. Similar changes were also shown to occur in bone marrow. The possible significance of these responses in relation to acquired tick resistance in guinea pigs is discussed. 相似文献
55.
Allen JF 《Science (New York, N.Y.)》2003,299(5612):1530-1532
56.
1. A readily identifiable strain of Escherichia coli K12 was used as a 'marker' organism to determine the sources, routes and patterns of microbial cross-contamination during mechanical defeathering of broiler chicken carcases. 2. Inoculation of scald water with the marker organism led to a relatively even pattern of carcase contamination during subsequent defeathering. Microbial cross-contamination was greater by this route of inoculation than by either surface inoculation of a 'seeder' carcase or oral inoculation of a live bird one day before slaughter. 3. Dispersal of the marker organism was strongly influenced by the mechanical action of the defeathering machines. Forward transmission of the marker occurred by aerosol or large airborne droplets and particulates such as feathers. Moving carcases through the defeathering machines when these were non-operational clearly reduced backward transmission of the marker. 4. Although microbial dispersal was unaffected by increasing the spacing between individual carcases or installing a water curtain at the entry and exit of the defeathering machines, shielding of carcases with aluminium baffles reduced counts of the marker organism from contaminated carcases by > 90%. 5. The results imply that microbial cross-contamination of broiler chicken carcases during defeathering occurs mainly via the airborne route, which could be contained by physical means. 相似文献
57.
58.
59.
REASONS FOR PERFORMING STUDY: The normality of equine placentation is essential for fetal health and development. Substantial information exists on the gross morphological status of the placenta but few studies have addressed the problem of degenerative lesions that interfere with placental morphology and placental efficiency. HYPOTHESIS: Degenerative changes in the endometrium with increasing age and parity are reflected in the morphology and density of the placental microcotyledons. OBJECTIVE: To assess placental efficiency on the basis of foal birthweight as a function of total microscopic area of fetomaternal contact. METHODS: Stereology was used to examine the placentae of 84 Thoroughbred mares grouped on the basis of age and parity. Placental efficiency, assessed by expressing foal birthweight as a function of total microscopic area of fetomaternal contact, was also determined. RESULTS: Mare age and parity influenced the development of the microcotyledons and microcotyledon surface density (Sv) was lowest in aged multiparous mares, presumably due to degenerative changes in their endometrium. However, primiparous mares also showed significantly lower Sv values than young multiparous mares, despite the virginal endometrium of the former group. This apparent 'priming' effect of a first pregnancy on microcotyledonary Sv was illustrated further by 11 maiden mares followed in 2 successive pregnancies. They all showed significant increases in Sv values in their second parity, with equivalent improvements in foal birthweight. CONCLUSIONS: Foal birthweight is a reflection of the balance between fetomaternal contact and placental efficiency. Increases in fetomaternal contact are correlated to reductions in placental efficiency, which may reflect the ability of the placenta to modify its exchange capabilities. POTENTIAL RELEVANCE: Further work is needed to elucidate how such changes in microcotyledon morphology and efficiency are brought about. 相似文献
60.
Heath AM Carson RL Purohit RC Sartin EM Wenzel JG Wolfe DE 《Journal of the American Veterinary Medical Association》2002,220(4):507-512
OBJECTIVE: To determine whether testicular needle biopsy is detrimental to testicular function in clinically normal bulls. DESIGN: Prospective study. ANIMALS: 6 mixed-breed mature bulls. PROCEDURE: A randomly selected testicle from each bull was biopsied with a 14-gauge needle biopsy instrument. Bulls were then evaluated over a 90-day period for changes in scrotal temperature and thermal patterns, ultrasonographic appearance, and quality of spermatozoa. At the end of the 90-day study, bulls were castrated, and testicles were examined grossly and histologically. RESULTS: Changes were detected in scrotal temperatures and thermal patterns and in the breeding soundness examination results during the first 2 weeks of the study. However, there were no long-term changes in semen quality over the course of the experiment. Hyperechoic areas were detected on ultrasonographic examination and corresponded to the areas of penetration by the biopsy instrument. Microscopic lesions that were indicative of testicular dysfunction were not found. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that testicular biopsy is a safe procedure in bulls. Testicular biopsy could possibly be used to further examine bulls that have less than satisfactory results for breeding soundness examinations. 相似文献