全文获取类型
收费全文 | 231864篇 |
免费 | 12515篇 |
国内免费 | 174篇 |
专业分类
林业 | 9327篇 |
农学 | 7292篇 |
基础科学 | 1544篇 |
28671篇 | |
综合类 | 40755篇 |
农作物 | 8999篇 |
水产渔业 | 11580篇 |
畜牧兽医 | 117103篇 |
园艺 | 3089篇 |
植物保护 | 16193篇 |
出版年
2018年 | 3136篇 |
2017年 | 3547篇 |
2016年 | 3249篇 |
2015年 | 2751篇 |
2014年 | 3484篇 |
2013年 | 8915篇 |
2012年 | 6432篇 |
2011年 | 8001篇 |
2010年 | 5139篇 |
2009年 | 5257篇 |
2008年 | 7831篇 |
2007年 | 7467篇 |
2006年 | 7059篇 |
2005年 | 6546篇 |
2004年 | 6325篇 |
2003年 | 6440篇 |
2002年 | 6040篇 |
2001年 | 7118篇 |
2000年 | 6962篇 |
1999年 | 5594篇 |
1998年 | 2402篇 |
1997年 | 2377篇 |
1996年 | 2219篇 |
1995年 | 2703篇 |
1994年 | 2418篇 |
1993年 | 2306篇 |
1992年 | 4667篇 |
1991年 | 4882篇 |
1990年 | 4835篇 |
1989年 | 4837篇 |
1988年 | 4443篇 |
1987年 | 4526篇 |
1986年 | 4665篇 |
1985年 | 4510篇 |
1984年 | 3725篇 |
1983年 | 3364篇 |
1982年 | 2334篇 |
1981年 | 2154篇 |
1979年 | 3458篇 |
1978年 | 2875篇 |
1977年 | 2421篇 |
1976年 | 2327篇 |
1975年 | 2471篇 |
1974年 | 3057篇 |
1973年 | 3107篇 |
1972年 | 2975篇 |
1971年 | 2695篇 |
1970年 | 2546篇 |
1969年 | 2508篇 |
1967年 | 2159篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
931.
M L Day K Imakawa A C Clutter P L Wolfe D D Zalesky M K Nielsen J E Kinder 《Journal of animal science》1987,65(5):1207-1212
Two experiments were performed to test the hypothesis that suckling behavior of calves with similar growth potential varies depending on cows' level of estimated milk production and stage of lactation. Eleven mature cows, which varied in estimated 205-d milk production (996 to 2354 kg/205 d), nursing heifer calves of similar growth potential were used in Exp. 1. Suckling behavior of calves was observed for two 24-h periods at three stages of lactation (average of 52, 104 and 167 d postpartum). Suckling frequency (suckling bouts/24 h) declined as milk production increased at 52 d of lactation (-.00382 bouts/kg milk) but was unrelated to milk production at later stages. Duration of suckling (minutes/suckling bout) increased with estimated level of milk production at all stages of lactation (means = .001556 min/kg milk). Total time suckling tended to increase as estimated level of milk production decreased at 52 d of lactation, but this component of suckling behavior was unaffected by milk level at later stages. Suckling frequency declined from 8.6 bouts/24 h at 52 d of lactation to 4.5 bouts/24 h at 167 d of lactation when averaged across all cows. Total minutes nursed/24 h declined in a similar manner (64 min/24 h to 44 min/24 h) between 52 and 167 d of lactation. Duration of each suckling bout did not change with stage. In the second experiment the relationship of suckling behavior to estimated milk production was evaluated at four early stages (average of 17, 38, 59 and 80 d postpartum) of lactation using 20 mature cows.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
932.
933.
934.
Multiple hereditary ocular anomalies in a herd of cattle 总被引:1,自引:0,他引:1
R L Kaswan L G Collins J L Blue C L Martin 《Journal of the American Veterinary Medical Association》1987,191(1):97-99
A Brahman x Santa Gertrudis herd of cows bred to a Hereford bull was evaluated because of a 3-year history of several calves born with congenital blindness. Multiple congenital ocular anomalies in 2 calves included microphthalmos, microcornea, microcoria, heterochromia iridis, microlentia, cataracts, retinal dysplasia, retinal detachment, anterior segment dysgenesis, acorea, and proliferation of the anterior neuroectoderm. On the basis of the lack of environmental factors and persistence of an intermittent problem when breeding to a single bull, a genetic defect was diagnosed as the probable cause. Dominant inheritance with varied expressivity may have best explained the lack of obvious signs in the bull, with emergence of various anterior and posterior segment defects in offspring from unrelated cows. 相似文献
935.
Limiting amino acids in an 11% crude protein corn-soybean meal diet for growing pigs 总被引:1,自引:0,他引:1
Three experiments were conducted to test the hypothesis that methionine, isoleucine, valine or nitrogen either singly or in combination are limiting in an 11% crude protein, lysine-tryptophan-threonine-supplemented, corn-soybean meal diet for growing pigs. A 16% crude protein diet was used as a positive control in each experiment and all amino acid additions were made, at a minimum, to equal requirements. Average initial weights were 21.3 kg, 23.0 kg and 19.1 kg in Exp. 1, 2 and 3, respectively. The experiments averaged 4 wk in duration. In Exp. 1 and 2, neither the addition of glutamic acid as a source of nitrogen, nor methionine to the 11% diet resulted in any improvement (P greater than .20) in rate or efficiency of growth. Addition of the combination of isoleucine and valine to the 11% diet resulted in an increase (P less than .05) in both growth rate and feed efficiency to a level not different (P greater than .20) from that of the pigs consuming the positive control diet. The addition of valine to the 11% crude protein diet with supplemental lysine, tryptophan and threonine (Exp. 3) caused an improvement in daily gain (P less than .05) but not feed efficiency (P greater than .10). Isoleucine addition tended to reduce pig performance. The results of these experiments suggest that an 11% crude protein, corn-soybean meal diet fortified with lysine, tryptophan and threonine is not limiting in sulfur amino acids or nitrogen. Valine may be the only limiting amino acid. 相似文献
936.
M. J. DAY W. J. PENHALE R. P. McKENNA J. N. MILLS D. A. PASS 《The Journal of small animal practice》1987,28(2):147-156
Clinical and laboratory findings are presented from two cases of canine IgA multiple myeloma. One of these animals presented with typical clinical and pathological changes including haematological abnormalities and skeletal lesions with secondary invasion of other organs. In contrast, the primary focus of disease in the second dog was the anterior alimentary tract and there were no skeletal changes. In this respect this second case was similar to the condition in man known as alpha chain disease. The two paraproteins differed in electrophoretic mobility. 相似文献
937.
938.
MARCY J. SOUZA JONATHAN S. WALL ALAN STUCKEY GREGORY B. DANIEL 《Veterinary radiology & ultrasound》2011,52(3):340-344
Positron emission tomography (PET) is often used to stage and monitor human cancer and has recently been used in a similar fashion in veterinary medicine. The most commonly used radiopharmaceutical is 2‐Deoxy‐2‐[18F]‐Fluoro‐d ‐glucose (18F‐FDG), which is concentrated and trapped within cells that use glucose as their energy substrate. We characterized the normal distribution of 18F‐FDG in 10 healthy Hispaniolan Amazon parrots (Amazona ventralis) by performing whole body PET scans at steady state, 60 min after injection. Significant variability was found in the intestinal activity. Avian species are known to reflux fluid and electrolytes from their cloaca into their colon. To evaluate reflux as the cause of variability in intestinal distribution of 18F‐FDG, dynamic PET scans were performed on the coelomic cavity of six Hispaniolan Amazon parrots from time 0 to 60 min postinjection of radiotracer. Reflux of radioactive material from the cloaca into the colon occurred in all birds to varying degrees and occurred before 60 min. To evaluate the intestinal tract of clinical avian patients, dynamic scans must be performed starting immediately after injection so that increased radioactivity due to metabolism or hypermetabolic lesions such as cancer can be differentiated from increased radioactivity due to reflux of fluid from the cloaca. 相似文献
939.
Antigenic relatedness and partial amino acid sequences of pili of Escherichia coli serotypes O1, O2, and O78 pathogenic to poultry 总被引:6,自引:0,他引:6
Pilus proteins from Escherichia coli serotypes O1, O2, and O78 pathogenic to poultry were compared with regard to their antigenic relatedness and partial amino acid sequences. Agglutination, immunodiffusion, and immunoblot assays with polyclonal antibodies to these pili showed that these pili not only share some common antigens but also contain antigens unique to each pilus. The partial amino-terminal amino acid sequences support our earlier findings that the pili are different but contain some structural homologies. 相似文献
940.
In a pilot survey to compare the relative prevalence of three diseases in apparently healthy White Fulani Zebu (WFZ) cattle slaughtered in Nigeria, sera from 80 randomly selected animals with no significant gross lesions on ante mortem and post mortem inspection were examined for antibodies to Brucella abortus, Dermatophilus congolensis and bovine leukaemia virus. Of the samples screened, 5.0, 8.8 and 2.0% showed serological evidence for brucellosis, cutaneous streptothricosis and bovine leukosis respectively. 相似文献