全文获取类型
收费全文 | 601篇 |
免费 | 34篇 |
专业分类
林业 | 36篇 |
农学 | 12篇 |
98篇 | |
综合类 | 52篇 |
农作物 | 15篇 |
水产渔业 | 25篇 |
畜牧兽医 | 344篇 |
园艺 | 21篇 |
植物保护 | 32篇 |
出版年
2023年 | 13篇 |
2022年 | 13篇 |
2021年 | 18篇 |
2020年 | 30篇 |
2019年 | 35篇 |
2018年 | 15篇 |
2017年 | 14篇 |
2016年 | 19篇 |
2015年 | 18篇 |
2014年 | 19篇 |
2013年 | 26篇 |
2012年 | 43篇 |
2011年 | 55篇 |
2010年 | 30篇 |
2009年 | 21篇 |
2008年 | 32篇 |
2007年 | 40篇 |
2006年 | 45篇 |
2005年 | 26篇 |
2004年 | 32篇 |
2003年 | 28篇 |
2002年 | 22篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有635条查询结果,搜索用时 31 毫秒
551.
552.
Robert M. Hubbard James M. Vose Barton D. Clinton Katherine J. Elliott Jennifer D. Knoepp 《Forest Ecology and Management》2004,190(2-3):311-321
Understory prescribed burning is being suggested as a viable management tool for restoring degraded oak–pine forest communities in the southern Appalachians yet information is lacking on how this will affect ecosystem processes. Our objectives in this study were to evaluate the watershed scale effects of understory burning on total aboveground biomass, and the carbon and nitrogen pools in coarse woody debris (CWD), forest floor and soils. We also evaluated the effects of burning on three key biogeochemical fluxes; litterfall, soil CO2 flux and soil net nitrogen mineralization. We found burning significantly reduced understory biomass as well as the carbon and nitrogen pools in CWD, small wood and litter. There was no significant loss of carbon and nitrogen from the fermentation, humus and soil layer probably as the result of low fire intensity. Burning resulted in a total net loss of 55 kg ha−1 nitrogen from the wood and litter layers, which should be easily replaced by future atmospheric deposition. We found a small reduction in soil CO2 flux immediately following the burn but litterfall and net nitrogen mineralization were not significantly different from controls throughout the growing season following the burn. Overall, the effects of burning on the ecosystem processes we measured were small, suggesting that prescribed burning may be an effective management tool for restoring oak–pine ecosystems in the southern Appalachians. 相似文献
553.
Davis MA Hancock DD Besser TE Daniels JB Baker KN Call DR 《Veterinary microbiology》2007,119(2-4):221-230
Salmonella enterica serovar Dublin (S. Dublin) is a cattle-adapted Salmonella serovar, so if antimicrobial resistance in S. Dublin arises as a result of antimicrobial use this most likely occurs within the cattle reservoir without impact from antimicrobial use in humans. We tested the antimicrobial resistance of bovine-origin S. Dublin isolates from 1986 through 2004 using a standard disk diffusion method. High proportions of isolates throughout the time period were resistant to one or more antimicrobials, and a marked increase in resistance to ceftazidime occurred between 2000 and 2004. Dairy-origin isolates were more likely to be resistant to several antibiotics than were isolates from beef operations where exposure to antimicrobials is likely to be less frequent. Plasmid analysis of a subset of isolates also supported the hypothesis that antimicrobial resistance traits in the cattle-adapted serovar Dublin were acquired within the bovine host environment. 相似文献
554.
Evoniuk JM Berg PT Johnson ML Larson DM Maddock TD Stoltenow CL Schauer CS O'Rourke KI Redmer DA 《American journal of veterinary research》2007,68(10):1073-1078
OBJECTIVE: To determine whether selection for the homozygous A136 R171 genotype that confers resistance to classic scrapie infection negatively affects production traits in sheep. ANIMALS: 996 commercial lambs obtained from 2 flocks at separate locations across 3 consecutive years. Procedures-Genotyping at codon 136 and 171 was performed by use of commercially available testing or a single-nucleotide polymorphism assay. Carcass data were collected without knowledge of genotype approximately 24 hours after slaughter by an experienced grader. The model to analyze associations between prion protein (PRNP) genotype and production traits was based on genotype, breed, or both as fixed effects and days on feed as a covariate. RESULTS: Average daily gain was significantly associated with only combined codons 136 and 171. In flock 1, weaning average daily gain was significantly greater in AA136 sheep than heterozygotes; the difference between QR171 and RR171 sheep, compared with QQ171 sheep, were not significant although QR171 and RR171 sheep had higher values. However, in flock 2, average daily gain was significantly greater in AV136 sheep than AA136 sheep and in QR171 sheep than QQ171 sheep. CONCLUSIONS AND CLINICAL RELEVANCE: Findings suggest there is an advantage for average daily gain in lambs with an arginine allele at codon 171, but there were no other genotype effects on production traits. Thus, selection for the resistant arginine allele at codon 171 to comply with USDA scrapie eradication guidelines should not be detrimental to lamb production in commercial flocks. Effects of codon 136 on average daily gain were ambiguous. 相似文献
555.
Biologic variability in NT‐proBNP and cardiac troponin‐I in healthy dogs and dogs with mitral valve degeneration
下载免费PDF全文
![点击此处可从《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
556.
Mery de la Fuente Paz Jopia Gerardo González-Rocha Nicolás Guiliani Katherine Sossa 《Journal of aquatic animal health》2015,27(2):112-122
The main goal of this study was to find bacterial isolates with the ability to inhibit the growth of the fish pathogens Aeromonas hydrophila, Vibrio anguillarum, and Flavobacterium psychrophilum and to inhibit the blockage of the quorum-sensing (QS) system. A total of 80 gram-negative strains isolated from various freshwater Chilean salmonid farms were studied. We determined that 10 strains belonging to the genus Pseudomonas inhibited at least one of the assayed fish pathogens. Of these, nine strains were able to produce siderophores and two strains were able to inhibit the growth of all assayed pathogenic species. When the 80 strains were examined for QS-blocking activity, only the strains Pseudomonas sp. FF16 and Raoultella planticola R5B1 were identified as QS blockers. When the QS-blocker strains were analyzed for their ability to produce homoserine lactone (HSL) molecules, thin-layer chromatography analysis showed that both strains were able to produce C6-HSL– and C8-HSL–type molecules. Strain R5B1 did not show growth inhibition properties, but strain FF16 also led to inhibition of growth in A. hydrophila and F. psychrophilum as well as to siderophore production. Pseudomonas sp. FF16 exhibited potentially useful antagonistic properties and could be a probiotic candidate for the salmon farming industry.
Received July 31, 2014; accepted December 17, 2014 相似文献
557.
Katherine M Koch Robert C Thaler Sam K Baidoo Crystal L Levesque Rebecca C Bott 《畜牧与生物技术杂志(英文版)》2015,6(1)
Background
A novel extruded product was characterized with a metabolism and lactation trial to establish the product’s energy content, and its effects on lactating sow performance. The product was composed of a 60:40 corn-soybean blend, which was then extruded. This product containing the co-extruded 60:40 corn-soybean blend was commercially developed and is used extensively in swine diets in southwest Minnesota. GE of dietary treatments were determined by isoperibol bomb calorimetry. Twelve barrows (59.9 ± 1.4 kg), were used to determine the digestible and metabolizable energy of the extruded product. DE of treatments was determined by subtracting fecal energy from GE provided to barrows by each respective treatment. ME was determined by subtracting urinary energy from calculated digestible energy. Sixty-three sows were used for the lactation trial. Three dietary treatments were utilized: CONTROL (an industry standard diet); PRODUCT (contained the product, vitamins and minerals); OIL (matched the lysine:ME ratio of PRODUCT by addition of soy oil). Sow weight, backfat thickness at the right and left last ribs, body condition score, number of piglets, and litter weights were recorded on the date of farrowing (d 0), (d 9), and at weaning. Blood and milk samples were obtained at weaning, and blood was analyzed for plasma urea nitrogen (PUN), milk was analyzed for total protein and fat content.Results
On a dry-matter basis, the test diet provided 3,908 kcal/kg DE and 3,833 kcal/kg ME, which was significantly greater than the basal diet, which provided 3,633 kcal/kg DE and 3,567 kcal/kg ME (P < 0.0001). These data were used to establish the DE and ME of the product, which were 3,882 kcal/kg and 3,798 kcal/kg, respectively, on an as-fed basis. No effect of diet was observed for changes in sow backfat (RBF P = 0.24; LBF P = 0.07) or body condition score (P = 0.12) during lactation. Milk total protein (P = 0.69), fat (P = 0.66), PUN, average piglet gain (P = 0.55) and piglet mortality (P = 0.70) did not differ between treatments.Conclusions
While the novel extruded product was higher in energy content than traditional feedstuffs, it resulted in the same lactational sow performance. Thus, the co-extruded corn-soybean product is a reasonable inclusion in sow lactation diets. 相似文献558.
Biomarkers for differentiation of causes of respiratory distress in dogs and cats: Part 2 – Lower airway,thromboembolic, and inflammatory diseases
下载免费PDF全文
![点击此处可从《Journal of Veterinary Emergency and Critical Care》网站下载免费的PDF全文](/ch/ext_images/free.gif)
559.
Biomarkers for differentiation of causes of respiratory distress in dogs and cats: Part 1 – Cardiac diseases and pulmonary hypertension
下载免费PDF全文
![点击此处可从《Journal of Veterinary Emergency and Critical Care》网站下载免费的PDF全文](/ch/ext_images/free.gif)
560.
Paul Pauline Cole Betty Ives Knight Katherine G. 《American Journal of Potato Research》1950,27(5):189-198
American Journal of Potato Research - 相似文献