全文获取类型
收费全文 | 945篇 |
免费 | 54篇 |
专业分类
林业 | 54篇 |
农学 | 32篇 |
基础科学 | 4篇 |
143篇 | |
综合类 | 241篇 |
农作物 | 35篇 |
水产渔业 | 35篇 |
畜牧兽医 | 349篇 |
园艺 | 21篇 |
植物保护 | 85篇 |
出版年
2021年 | 10篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 15篇 |
2017年 | 14篇 |
2016年 | 24篇 |
2015年 | 11篇 |
2014年 | 21篇 |
2013年 | 31篇 |
2012年 | 34篇 |
2011年 | 49篇 |
2010年 | 24篇 |
2009年 | 20篇 |
2008年 | 35篇 |
2007年 | 36篇 |
2006年 | 34篇 |
2005年 | 37篇 |
2004年 | 33篇 |
2003年 | 38篇 |
2002年 | 35篇 |
2001年 | 20篇 |
2000年 | 24篇 |
1999年 | 20篇 |
1998年 | 8篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1993年 | 10篇 |
1992年 | 29篇 |
1991年 | 41篇 |
1990年 | 34篇 |
1989年 | 10篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1983年 | 8篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 14篇 |
1972年 | 12篇 |
1971年 | 10篇 |
1970年 | 17篇 |
1969年 | 10篇 |
1968年 | 7篇 |
1967年 | 7篇 |
排序方式: 共有999条查询结果,搜索用时 140 毫秒
1.
Chaiyan Kasorndorkbua Brad J. Thacker Patrick G. Halbur Denis K. Guenette Ryan M. Buitenwerf Ryan L. Royer Xiang-Jin Meng 《Canadian journal of veterinary research》2003,67(4):303-306
To determine the effect of swine hepatitis E virus (HEV) infection on pregnant gilts, their fetuses, and offspring, 12 gilts were intravenously inoculated with swine HEV. Six gilts, who were not inoculated, served as controls. All inoculated gilts became actively infected and shed HEV in feces, but vertical transmission was not detected in the fetuses. There was no evidence of clinical disease in the gilts or their offspring. Mild multifocal lymphohistiocytic hepatitis was observed in 4 of 12 inoculated gilts. There was no significant effect of swine HEV on fetal size, fetal viability, or offspring birth weight or weight gain. The offspring acquired anti-HEV colostral antibodies but remained seronegative after the antibodies waned by 71 days of age. Swine HEV infection induced subclinical hepatitis in pregnant gilts, but had no effect on the gilts' reproductive performance, or the fetuses or offspring. Fulminant hepatitis associated with HEV infection was not reproduced in gilts. 相似文献
2.
3.
DNA fingerprinting with the probes 33.15 and alpha-globin 3'HVR has been used to resolve three cases of disputed paternity in dogs. For each pedigree it was necessary to establish which bands in the DNA fingerprints of the offspring were of paternal origin, and then establish which putative sire carried all these bands. In the first case, a litter of Rhodesian Ridgebacks, twelve DNA bands were informative in establishing paternity. In the second case, a litter of Afghan hounds, five DNA bands established paternity, Lastly, in a litter of Border collies, five DNA bands established paternity. In each case a single dog only sired the entire litter. 相似文献
4.
5.
1. The egg does not completely obey Hook's law when compressed between flat surfaces.
2. Deformation was not completely reversible due to crumbling at the points of contact with the force.
3. There are three components of non‐destructive deformation: (a) local deformation at the points of contact, (b) local surface crumbling and (c) deformation of the over‐all shell structure.
4. The latter two are uncontrolled, contributing to errors in the prediction of fracture force and depending on the non‐destructive force applied.
5. These effects should be considered in test selection and interpretation.
6. The optimum non‐destructive force was found to be 1 kg. 相似文献
6.
Denis J. Sonwa Ousmane Coulibaly A. Akinwumi Adesina Stephan F. Weise Mathurin Tchatat 《Integrated Pest Management Reviews》2002,7(3):191-199
Imports of pesticides have long been subsidised for use in the cocoa agroforests of the humid forest zone of southern Cameroon.
With the liberalisation of the cocoa and pesticides sectors and the devaluation of the local currency (CFA franc), farmers
are facing fluctuations in the price paid for cocoa and the high cost of farm inputs. Without the support of the extension
services, they themselves have developed traditional integrated control methods based on the use of plant extracts mixed with
conventional pesticides. From a survey of 300 cocoa farmers, the study assesses the farmers' command of these methods, the
pests controlled, the problems encountered and the institutional constraints in the definition and dissemination of integrated
control methods. The study concludes with recommendations for research and development towards the better definition and dissemination
of integrated control methods.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Validity of goniometric joint measurements in cats 总被引:2,自引:0,他引:2
Jaeger GH Marcellin-Little DJ Depuy V Lascelles BD 《American journal of veterinary research》2007,68(8):822-826
OBJECTIVE: To compare and validate goniometric joint measurements obtained from nonsedated and sedated cats with measurements from radiographic evaluation. ANIMALS: 20 adult cats with no evidence of joint disease. PROCEDURES: Measurements of flexion and extension of the carpus, elbow, shoulder, tarsus, stifle, and hip joints and of carpal and tarsal joints during varus and valgus angulation were made by a single investigator before and after sedation of cats. Measurements were made by use of a goniometer with a masked dial. Joint angle measurements were compared between nonsedated and sedated cats and also with measurements from radiographs made while cats were sedated. Each series of measurements was repeated 4 times. To evaluate repeatability, Cronbach alpha values were calculated for repeated measure results of goniometric joint measurements of nonsedated and sedated cats. An intraclass correlation was calculated to determine reliability among the 3 measurement types (ie, measurements from nonsedated and sedated cats and on radiographic evaluation). RESULTS: Joint measurements did not differ significantly by measurement type, when comparing radiographic measurements with goniometric measurements in sedated and nonsedated cats. Cronbach alpha values were > 0.99 for goniometric joint measurements within individual nonsedated and sedated cats and also for comparison of mean measurements obtained from sedated cats versus nonsedated cats versus radiographs. An intraclass correlation of 0.999 revealed high reliability among measurement types. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that goniometric joint measurements in nonsedated and sedated cats are repeatable and valid. 相似文献
8.
Kobayashi Y Inoue N Sato G Itou T Santos HP Brito CJ Gomes AA Santos MF Silva MV Mota CS Ito FH Sakai T 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2007,69(7):691-696
The incidence of canine rabies has been widely reported in Brazil, and new rabies virus (RV) variants, genetically similar to canine RV, have recently been isolated from foxes. In order to derive the epidemiological characteristics of Brazilian Carnivora RV, Brazilian RVs isolated from dogs, cats, and foxes were genetically analyzed. Brazilian Carnivora RV isolates were divided into 2 main lineages. The predominant lineage was found in dogs and cats, which included the Argentinean and Bolivian Carnivora RV isolates, and was extensively distributed throughout Brazil and surrounding countries. The other lineage consisted of three sublineages containing Brazilian dog and fox RV isolates, with the dog sublineages located on an internal branch of 2 fox sublineages, suggesting that RV transmission events might have occurred between foxes and dogs in the past. These results suggest that contact between dogs and wildlife has the potential to generate new rabies variants and that it is important to control RV infection cycles in both dogs and wildlife to prevent spread of rabies infection. 相似文献
9.
Though microbial activity is known to occur in frozen soils, little is known about the fate of animal manure N applied in the fall to agricultural soils located in areas with prolonged winter periods. Our objective was to examine transformations of soil and pig slurry N at low temperatures. Loamy and clay soils were either unamended (Control), amended with 15NH4-labeled pig slurry, or amended with the pig slurry and wheat straw. Soils were incubated at −6, −2, 2, 6, and 10 °C. The amounts of NH4, NO3 and microbial biomass N (MBN), and the presence of 15N in these pools were monitored. Total mineral N, NO3 and 15NO3 increased at temperature down to −2 °C in the loam soil and −6 °C in the clay soil, indicating that nitrification and mineralization proceeded in frozen soils. Nitrification and mineralization rates were 1.8-4.9 times higher in the clay than in the loamy soil, especially below freezing point (3.2-4.9), possibly because more unfrozen water remained in the clay than in the loamy soil. Slurry addition increased nitrification rates by 3-14 times at all temperatures, indicating that this process was N-limited even in frozen soils. Straw incorporation caused significant net N immobilization only at temperatures ≥2 °C in both soils; the rates were 1.4-3.4 higher in the loam than in the clay soil. Nevertheless, up to 30% of the applied 15N was present in MBN at all temperatures. These findings indicate that microbial N immobilization occurred in frozen soils, but was not strong enough to induce net immobilization below the freezing point, even in the presence of straw. The Q10 values for estimated mineralization and nitrification rates were one to two orders-of-magnitude larger below 2 °C than above this temperature (13-208 versus 1.5-6.9, respectively), indicating that these processes are highly sensitive to a small increase in soil temperature around the freezing point of water. This study confirms that net mineralization and nitrification can occur at potentially significant rates in frozen agricultural soils, especially in the presence of organic amendments. In contrast, net N immobilization could be detected essentially above the freezing point. Our results imply that fall-applied N could be at risk of overwinter losses, particularly in fine-textured soils. 相似文献
10.
A yield-independent, 15N-isotope dilution method to estimate legume symbiotic dependence without a non-N2-fixing reference plant 总被引:1,自引:0,他引:1
P. M. Chalk C. J. Smith P. Hopmans S. D. Hamilton 《Biology and Fertility of Soils》1996,23(2):196-199
The proportional contribution of atmospheric N2 to the N nutrition of lupin (P
atm) was estimated in a field experiment following addition of NH4Cl of KNO3 to unconfined microplots (1.5 m2) at 2.5 g N m-2 (10 atom% 15N). The integrated 15N enrichment, or mean pool abundance, of nitrate extracted from 0- to 15-cm samples taken under the lupin crop on eight occasion between 28 and 190 days after sowing was used as the reference criterion to estimate P
atm by the 15N-isotope dilution technique. Estimates of P
atm were similar to those obtained using canola as a non-fixing reference plant, but were higher than estimates obtained using a yield-dependent model. Use of mean pool abundance obviates the need for a non-fixing reference plant, and the frequent sampling and isotope-ratio analysis of the legume biomass required with the yield-dependent model is unnecessary. However, further work is needed to validate a sampling strategy commensurate with the growth of the legume roots. 相似文献