全文获取类型
收费全文 | 409篇 |
免费 | 23篇 |
专业分类
林业 | 30篇 |
农学 | 9篇 |
85篇 | |
综合类 | 32篇 |
农作物 | 11篇 |
水产渔业 | 47篇 |
畜牧兽医 | 212篇 |
园艺 | 1篇 |
植物保护 | 5篇 |
出版年
2020年 | 5篇 |
2019年 | 12篇 |
2018年 | 5篇 |
2017年 | 13篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 16篇 |
2012年 | 13篇 |
2011年 | 14篇 |
2010年 | 9篇 |
2008年 | 14篇 |
2007年 | 14篇 |
2006年 | 14篇 |
2005年 | 22篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 3篇 |
1972年 | 7篇 |
1971年 | 6篇 |
1970年 | 9篇 |
1969年 | 10篇 |
1968年 | 13篇 |
1967年 | 6篇 |
1966年 | 4篇 |
1957年 | 2篇 |
排序方式: 共有432条查询结果,搜索用时 31 毫秒
21.
K Eulenberger K Eulenberger J Schulz M Wolf 《DTW. Deutsche tier?rztliche Wochenschrift》1990,97(10):387-390
The effects of metaphylactic measures in cattle herds with the aim of diminishing puerperal disturbances and ensurement of high reproductive performance were studied. About 5000 cows in more than 30 groups (experimental and controls) were included into the clinical investigations. Dietary supplementation by sodium propionic acid over a period of 4 weeks, oxytocin or parasympathomimetics administered during the first 3 days post partum had a certain metaphylactic effect, only when the therapeutic principle met the prevalent cause of the given puerperal disturbance. In herds with high incidence of noninfectious retention of fetal membranes the metaphylactic application of Se and Vitamin E (10 days ante partum) can be taken into account. Stimulation of the ovarian activity by GnRH is recommended in animals which fail to have developed follicular activity by the 12th-15th day post partum. 相似文献
22.
23.
24.
25.
Hymenoscyphus pseudoalbidus is the causal agent of ash dieback, a disease that is presently endangering Fraxinus spp. throughout most of Europe. The phytotoxin, viridiol, was previously isolated from culture extracts of H. pseudoalbidus and found to be toxic to leaves of F. excelsior. Thus, we were interested in learning to what extent viridiol is responsible for pathogenicity of H. pseudoalbidus and investigated this using twelve isolates of H. pseudoalbidus. We also included five isolates of the closely related avirulent species, Hymenoscyphus albidus, in our studies. Some, but not all, isolates of H. pseudoalbidus and H. albidus produced measurable quantities of viridiol in culture. Three tests were used to determine to what extent viridiol concentration correlates with virulence: culture extracts were tested for activity in leaf segment tests and for inhibition of germination of seedlings of Fraxinus excelsior; virulence of the isolates was tested following infection of axenically cultured ash seedlings. Activity of the culture extracts varied, as did virulence of the isolates following inoculation into seedlings. No correlations were found between viridiol concentration and activities of culture extracts in leaf segment tests or in the germination test, nor between viridiol concentration and disease symptoms when inoculated into seedlings. However, activities of culture extracts in leaf segment and in the germination test correlated, as did the results of each of these tests with virulence in the infection experiment. Apparently, as yet unidentified factors other than the concentration of viridiol play important roles in the virulence of H. pseudoalbidus. 相似文献
26.
J. E. B. Cavaco J. G. D. Lambert R. W. Schulz H. J. Th. Goos 《Fish physiology and biochemistry》1997,16(2):129-138
In fish, sex steroids initiate and/or accelerate the maturation of the brain-pituitary-gonad axis. In order to obtain information
on the steroid milieu during the pubertal development of male African catfish, we have monitored the conversion of [3H]-pregnenolone and [3H]-androstenedione by testis and [3H]-pregnenolone by interrenal tissue fragmentsin vitro. Pubertal development occurs between two and six months of age. Testicular development proceeds through four main stages
that are characterised histologically by the presence of spermatogonia (stage I), spermatogonia and spermatocytes (stage II),
spermatogonia, spermatocytes and spermatids (stage III), and all germ cells including spermatozoa (stage IV). 11β-Hydroxyandrostenedione
and cortisol were the main products of testes and interrenal tissue, respectively, in all stages of the pubertal development;
a change in the steroidogenic pattern was not observed during this period. The interrenal tissue displayed no significant
conversion of [3H]-pregnenolone to 11-oxygenated androgens. Blood plasma was analyzed for the presence of five androgens; testosterone, 11β-hydroxytestosterone,
11β-hydroxyandrostenedione, androstenetrione, and 11-ketotestosterone. 11-Ketotestosterone was the quantitatively dominating
androgen in the circulation at all stages of development, which was more pronounced in stages III and IV. The obvious differences
between thein vitro andin vivo results, namely 11β-hydroxyandrostenedione being the main testicular productvs. 11-ketotestosterone dominating in the blood, may indicate that 11β-hydroxyandrostenedione is converted to 11-ketotestosterone
at extratesticular sites. 相似文献
27.
Sertoli cell proliferation occurs mainly during the phase of rapid spermatogonial proliferation, allowing the cyst-forming Sertoli cells to form an increasingly large space for housing the growing germ cell clone. There is no information in fish on the regulation of Sertoli cell proliferation; follicle-stimulating hormone (FSH) stimulates Sertoli cell proliferation in mammals. Increasing or decreasing FSH and FSH receptor expression experimentally in male African catfish was associated with respective changes in Sertoli cell proliferation or testis growth, suggesting that also in fish, one role of FSH may be to regulate Sertoli cell numbers. 相似文献
28.
Optical light, transmission, and scanning electron microscopy were used in investigations of epithelia in the glandular region of the milk cistern and greater lactiferous ducts and yielded the following findings, four and six hours from infection: degeneration and necrosis of epithelial cells, intraepithelial foreign cell infiltration (neutrophilic granulocytes, lymphocytes, macrophages), intra-epithelial oedema and locally delimited epithelial loss. The lesions differed by intensity in various regions, so that a distinction could be made among five froms of epithelial alterations. The epithelial cells revealed their capability of absorbing pathogenic material and storing it in cytoplasmic vacuoles. This was considered to reflect active involvement of epithelium in antibacterial defence, and consequently, to reflect the role played by epithelium as a defence barrier in the milk cistern and greater lactiferous ducts. 相似文献
29.
A feed loading experiment was applied in 2 phases to 45 young cocks over 12 weeks, using 1,2-N,N-bis(methylmercury)-p-toluolsulphamide-dressed wheat (50% of base ration). Investigations were conducted to study the effects of selenium supplementation (0,2 mg Se as sodium selenite/l drinking water) on biochemical and hematological parameters (calcium, phosphorus, total protein, albumin, creatinine, urea, activity of alkaline phosphatase, hematocrit, hemoglobin, leucocyte count) as well as on parameters relating to toxicological residues (selenium and mercury levels in liver, musculature and kidneys). Statistically secured differences were found to exist between the experimental groups with regard to selenium and mercury in the liver and mercury concentrations in kidneys. Possible interrelationships were discussed. 相似文献
30.