全文获取类型
收费全文 | 2049篇 |
免费 | 136篇 |
国内免费 | 1篇 |
专业分类
林业 | 135篇 |
农学 | 76篇 |
基础科学 | 14篇 |
278篇 | |
综合类 | 352篇 |
农作物 | 83篇 |
水产渔业 | 237篇 |
畜牧兽医 | 820篇 |
园艺 | 62篇 |
植物保护 | 129篇 |
出版年
2023年 | 17篇 |
2022年 | 11篇 |
2021年 | 39篇 |
2020年 | 56篇 |
2019年 | 60篇 |
2018年 | 63篇 |
2017年 | 57篇 |
2016年 | 48篇 |
2015年 | 45篇 |
2014年 | 62篇 |
2013年 | 85篇 |
2012年 | 111篇 |
2011年 | 163篇 |
2010年 | 79篇 |
2009年 | 64篇 |
2008年 | 118篇 |
2007年 | 117篇 |
2006年 | 105篇 |
2005年 | 102篇 |
2004年 | 117篇 |
2003年 | 115篇 |
2002年 | 96篇 |
2001年 | 30篇 |
2000年 | 15篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 18篇 |
1996年 | 9篇 |
1995年 | 25篇 |
1994年 | 14篇 |
1993年 | 8篇 |
1992年 | 20篇 |
1991年 | 27篇 |
1990年 | 11篇 |
1989年 | 20篇 |
1988年 | 10篇 |
1987年 | 26篇 |
1986年 | 15篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1973年 | 10篇 |
1972年 | 8篇 |
1970年 | 8篇 |
排序方式: 共有2186条查询结果,搜索用时 15 毫秒
91.
W.E. Marsh T. Damrongwatanapokin K. Larntz R.B. Morrison 《Preventive veterinary medicine》1991,11(3-4):249-254
A geographic information system (GIS) is being developed to study the spread of pseudorabies virus (PRV) among swine herds in the state of Minnesota. This GIS features an interface with a database management system that stores and manages pertinent data. These data include herd size, type of production system, degree of confinement, topographical features surrounding the farm, density of swine herds and distance to the closest quarantined herd. A pilot study was conducted in one Minnesota county with 280 swine herds, of which the PRV status was known in 115. Cox regression analysis was used to determine factors associated with herd PRV status. Relative risks (RR) and 95% confidence intervals (CI) were calculated. No association was detected between the PRV status of the herd and distance to the nearest county road, highway or quarantined herd. However, the following factors were significant: located within 1 km of a river or lake (RR, 0.524; CI, 0.328–0.828); farrow to finish (RR, 2.120; CI, 1.194–3.791); complete confinement (RR, 3.423; CI, 1.639–7.139); density of swine herds within a 5 km radius (RR, 1.036 per herd; CI, 0.996–1.064). 相似文献
92.
Abstract— Plasma concentrations of insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding proteins (IGFBPs) were compared between market sized sunshine and palmetto bass. Differences between male and female fish were examined and both hybrids were sampled before and after a low-water confinement stress. There was no difference in body weight between the hybrid types, however, females were significantly heavier than males in both hybrids. Plasma IGF-I concentrations were significantly higher in pre-stressed palmetto bass when compared with sunshine bass, and male palmetto bass had significantly higher IGF-I concentrations than females. Two hours after a 15-min low-water stress, a significant decrease in palmetto bass IGF-I occurred, but there was no change in sunshine bass IGF-I concentrations. Levels of a 33-kDa IGFBP were similar in pre-stressed palmetto bass when compared with sunshine bass; however, no differences due to gender were evident for either hybrid. Two hours after a 15-min low-water exposure, there was no change in the levels of a 33-kDa IGFBP in palmetto or sunshine bass. A more complete understanding of IGF-I, IGFBPs, and IGF-I receptors may be necessary to explain the role of IGF-I in regulating fish growth. 相似文献
93.
Abstract.— Similarities among multi-locus DNA fingerprints of five channel catfish Ictalurus punctatus strains and the ability to identify the strain of a fish based on its fingerprint pattern were investigated. Five restriction enzymes and 13 multi-locus DNA probes were screened to identify enzyme-probe combination useful for DNA fingerprinting channel catfish. Restriction enzymes Hinf I and Dpn II, in combination with probes (CAC)n, (CGC)n, (CTC)n, (ATCC)n, and (GATA)n, produced useful fingerprints (20–30 resolvable bands for each enzyme-probe combination). Thirty individuals (3 pools of 10 individuals each) from each of five channel catfish strains (albino, Mississippi normal, USDA-102, USDA-102 select, and USDA-103) were fingerprinted with all useful enzyme-probe combinations. Band sharing among samples was higher within strains than among strains and band sharing among strains was higher for strains whose breeding history indicated a high degree of relatedness. Individual fingerprints of 18 fish from each of the USDA-102 select and USDA-103 strains revealed no strain-specific bands, but several diagnostic bands (present at high frequencies in either USDA-102 select or USDA-103 strains and at a low frequencies in other strains) were identified. Band sharing at diagnostic bands was used to correctly identify fish as USDA-102 select or USDA-103 strains with 82% accuracy from fingerprints of 17 USDA-102 select strain fish, 18 USDA-103 strain fish, and 38 fish collected from three commercial farms. 相似文献
94.
Monoclonal antibodies (mAbs) specific for bovine CD4 and CD5 antigens have been found to identify polymorphic determinants on these molecules. In the case of CD5, mAb IL-A67 recognises one allotypic form of the antigen while four other CD5-specific mAbs in the workshop (CC17, CC29, BLT-1 and 8C11) recognise a second allotype. The CD4-specific mAbs submitted to the workshop reacted with the cells of all animals tested. However, a further two mAbs (CC26 and IL-A18) specific for CD4 were found to react with cells only from about 85% of animals tested. Sequential immuno-precipitation experiments together with family studies showed that the allotypes of CD4 and CD5 are both inherited in a simple Mendelian manner and are co-dominantly expressed. One of the CD5 allotypes was not detected in Bos taurus animals while the gene frequency of the second allotype was only about 10% in the B. indicus animals tested. The gene frequency of the CD4 allotype detected by CC26 and IL-A18 was similar in the two sub-species. 相似文献
95.
Kelly Hall DVM Brian J. McCluskey DVM MS Wayne Cunningham DVM MS 《Journal of Equine Veterinary Science》2001,21(6):284
Following reports of an increase in the number of Corynebacterium pseudotuberculosis infections in horses in the western counties of Colorado in 1997, an epidemiological assessment of the problem was conducted using a survey of premises with affected horses. No gender, age or breed predilections were found. Most diagnoses of disease were made in the summer or fall of 1997. Abscesses were reported to occur in various locations with a mean healing time of 77 days. A majority of premises owners reported potential contact of horses with sheep or goats. The days of lost use and treatment costs per case had a mean of 13 days and $139, respectively. 相似文献
96.
97.
David A. Morrison Ross S. Kingwell David J. Pannell Michael A. Ewing 《Agricultural Systems》1986,20(4):243-268
A whole-farm mathematical programming model has been built for dryland crop-livestock farms in Western Australia. The multidisciplinary approach used for model building is presented and the resulting model structure is described. It is a mixed integer programming model which represents, in some detail, the biological, technological and financial relationships of the farming system and stresses the interdependencies of enterprises. The model is used to investigate the extent to which positive interactions between different enterprises influence the optimal farm plan. The management issue considered is the division of land between crop and pasture production. It is concluded that, for the farming system considered, interactions do have an influence on profit and the optimal farm plan. 相似文献
98.
99.
Use of computed tomography to evaluate pathologic changes in the lungs of calves with experimentally induced respiratory tract disease 总被引:1,自引:0,他引:1
Lubbers BV Apley MD Coetzee JF Mosier DA Biller DS Mason DE Henao-Guerrero PN 《American journal of veterinary research》2007,68(11):1259-1264
OBJECTIVE: To optimize methods for the use of computed tomography (CT) to assess pathologic changes in the lungs of calves and to determine the effect of treatment on lung consolidation. ANIMALS: 10 male Holstein calves. PROCEDURES: Calves were anesthetized to facilitate CT imaging of the thorax. After initial images were obtained, pneumonia was induced in the calves by inoculation through a bronchoscope. Two calves were used in a preliminary study to refine the inoculation dose and optimize CT images. Four calves were administered florfenicol and 4 calves were untreated control animals. Serial images were obtained 24, 48, and 72 hours after inoculation. After final images were obtained, calves were euthanized, and lung consolidation was estimated by use of lung surface area scoring and water displacement. These estimates were compared with estimated lung consolidation obtained by use of CT. RESULTS: Calves had rapid disease progression. Percentage of lung consolidation was not significantly different between treatment groups for any of the estimation methods. Results of an ANOVA of the 3 assessment methods indicated significant differences among methods. Estimates of the percentage of lung consolidation obtained by use of surface area scoring and CT correlated well, whereas water displacement estimates correlated poorly with other methods of consolidation estimation. CONCLUSIONS AND CLINICAL RELEVANCE: Because of the correlation with other methods for estimation of lung consolidation, CT has the potential to be used to monitor disease progression in calves with experimentally induced respiratory tract disease. 相似文献
100.