全文获取类型
收费全文 | 503篇 |
免费 | 51篇 |
专业分类
林业 | 14篇 |
农学 | 8篇 |
基础科学 | 2篇 |
68篇 | |
综合类 | 103篇 |
农作物 | 15篇 |
水产渔业 | 25篇 |
畜牧兽医 | 276篇 |
园艺 | 18篇 |
植物保护 | 25篇 |
出版年
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 9篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 28篇 |
2012年 | 16篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 15篇 |
2008年 | 18篇 |
2007年 | 14篇 |
2006年 | 19篇 |
2005年 | 12篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 19篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 4篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1983年 | 12篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1971年 | 10篇 |
1967年 | 13篇 |
1965年 | 5篇 |
1963年 | 4篇 |
1960年 | 5篇 |
排序方式: 共有554条查询结果,搜索用时 93 毫秒
1.
铬在增强畜禽抗应激与免疫机能中的作用 总被引:3,自引:0,他引:3
铬是动物所必需的一种微量元素,在动物体内碳水化合物,蛋白质,脂肪的代谢起重要作用。近年来研究发现铬的抗应激和提高免疫机能上有特殊的作用。本文就这一热点问题进行综述。 相似文献
2.
J L Du Plessis C Gray M F Van Strijp 《The Onderstepoort journal of veterinary research》1992,59(4):337-338
A 3-fold increase in the numbers of Lyt-2+ T cells in the circulating blood of mice infected and re-infected with the Welgevonden stock of Cowdria ruminantium, as determined by flow cytometry, is supportive evidence that immunity in heartwater is cell-mediated. The rise in Lyt-2+ cells only after re-infection of the mice is further evidence that the development of immunity in heartwater is dependent on the unhindered and adequate replication of C. ruminantium. 相似文献
3.
4.
5.
Andrews GA Smith JE Gray M Chavey PS Weeks BR 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》1992,21(2):57-60
An improved serum ferritin assay for canine serum has been developed. It uses two monoclonal antibodies in a sandwich arrangement. Serum ferritin can be determined on undiluted canine sera with this assay. The recovery of ferritin added to canine serum ranged from 98 to 106%, the within-assay coefficient of variability was 3.3 to 4.5%, and the assay-to-assay variability was 9.8 to 10.2%. Serum ferritin from 61 apparently healthy dogs had a geometric mean of 252 ng/ml, with a range of 80 ng/ml to 800 ng/ml. 相似文献
6.
The distribution and excretion of [14C]alcohol-labeled cismethrin and bioresmethrin was determined after intravenous administration to rats. Initially the label distribution of both isomers was similar, but differences occurred at later times mainly due to the retention of 5-benzyl-3-furylcarboxylic acid, a metabolite of bioresmethrin, in high concentration in the blood. Retention of this metabolite accounted for the slower excretion of bioresmethrin label compared to cismethrin. After administration of either isomer, parent pyrethroid was rapidly cleared from the blood and liver, and both isomers rapidly entered the central nervous system reaching peak concentrations within 2–5 min. Brain cismethrin concentrations exceeding 3.5 nmol/g were associated only with animals showing tremors. These levels of cismethrin are maintained for up to 30 min but bioresmethrin was depleted more rapidly possibly due to brain metabolism. It is concluded that the low toxicity of bioresmethrin is possibly due to the inability of this isomer to interact with the site of action in the central nervous system and not, as previously suggested, primarily because of more rapid metabolism in the liver. 相似文献
7.
Direct ageing of fish can be a laborious and expensive task when age estimates from a large population are required, and often involves a degree of subjectivity. This study examined the application of general and generalized linear models that predict the age of fish from a range of efficiently and objectively measured covariates. The data sampled were from yellowfin bream (Acanthopagrus australis (Sparidae) (Owen, 1853)) and sand whiting (Sillago ciliata (Sillaginidae) Cuvier, 1829) populations from New South Wales, Australia. The covariates evaluated in the models were fish length, otolith weight, sex and location (the estuary from which the fish were sampled). Akaike Information Criteria were used for model selection and residual plots of the final models revealed a satisfactory fit to the observations. The best fitting model for each species included all covariates. An additional investigation considered whether general and generalized linear models that predict age from two different categories of biometric information outperform age-length keys with respect to subsequent estimates of total mortality from catch-curve analysis. The two categories of biometric information differed in the ease and cost with which the information could be collected. The first category only included fish length and location as covariates, whilst the second category also included otolith weight and sex. It was found that traditional age-length keys outperformed the predictive models that estimated age from only fish length and location, because the results from the models were prone to significant bias. However, when otolith weight and sex were added as covariates to the predictive models, some of them, including a generalized linear model with a Poisson-distributed response variable, performed similarly to the age-length key. Given that otolith weight and the sex of fish are cheaper to quantify than age from a sectioned otolith in many situations, general or generalized linear models may represent a cheaper and faster method of estimating mortality compared to age-length keys. Such models can also easily incorporate the influence of spatial, temporal and demographic variation. 相似文献
8.
Eastern grey squirrels (Sciurus carolinensis) and North American red squirrels (Tamiasciurus hudsonicus) were studied among wooded patches within an agricultural mosaic. Fifteen sites south of Ottawa, Canada, with differing landscape and local features were censused using tracking boards placed in a woods or wooded fencerow. Regression analyses of landscape compositional and physiognomic variables within a 1-km radius isolated the best predictors of grey and red squirrel abundance and activity. Grey squirrels were found in both small woods and fencerows in farm landscapes but were not found in large woods. A polynomial regression of wooded patch size explained 79% of the variance in grey squirrel abundance. Grey squirrel activity was correlated with the percent cover of soybeans in the landscape. Red squirrels were found in fencerows, small and large woods; activity was correlated with the percent cover of both woods and corn crop in the surrounding landscape. These results indicate that distributions of both species are influenced by multiple landscape elements, but that grey squirrels may rely on fragmented agricultural landscapes whereas red squirrels make more use of both native woodland and altered landscapes. 相似文献
9.
The metal content was determined in soil and vegetation around the eastern zone of the disused sulphur and copper mines at Avoca (southeast Ireland). A 250 m × 250 m grid survey was conducted covering a total area of 4 km2. The mining belt was in the centre of the investigated site and was sampled separately. Iron, Zn, Cu and Cd concentrations in soil and plant material were determined, in addition to soil organic matter content and soil pH. Soil samples taken from the spoil showed elevated Cu and Cd concentrations, and low soil pH and organic matter content. At least 50 per cent of the agricultural sites examined around the East Avoca Mine showed elevated soil Cu and Cd concentrations, whereas Zn and Fe soil concentrations were within the range for unpolluted soils. None of the vegetation analysed had elevated Zn, Cd, Fe or Cu concentrations. Overall there was no indication of serious metal contamination in either soils or vegetation surrounding the mine in spite of extensive dust deposition during open-pit mining activity 15–30 years ago. However, a plume of elevated Cu in the soil was identified, which originated from a large spoil heap and had been spread for some 2·0 km by the prevailing wind. 相似文献
10.
The mTOR-regulated phosphoproteome reveals a mechanism of mTORC1-mediated inhibition of growth factor signaling 总被引:1,自引:0,他引:1
Hsu PP Kang SA Rameseder J Zhang Y Ottina KA Lim D Peterson TR Choi Y Gray NS Yaffe MB Marto JA Sabatini DM 《Science (New York, N.Y.)》2011,332(6035):1317-1322
The mammalian target of rapamycin (mTOR) protein kinase is a master growth promoter that nucleates two complexes, mTORC1 and mTORC2. Despite the diverse processes controlled by mTOR, few substrates are known. We defined the mTOR-regulated phosphoproteome by quantitative mass spectrometry and characterized the primary sequence motif specificity of mTOR using positional scanning peptide libraries. We found that the phosphorylation response to insulin is largely mTOR dependent and that mTOR exhibits a unique preference for proline, hydrophobic, and aromatic residues at the +1 position. The adaptor protein Grb10 was identified as an mTORC1 substrate that mediates the inhibition of phosphoinositide 3-kinase typical of cells lacking tuberous sclerosis complex 2 (TSC2), a tumor suppressor and negative regulator of mTORC1. Our work clarifies how mTORC1 inhibits growth factor signaling and opens new areas of investigation in mTOR biology. 相似文献