全文获取类型
收费全文 | 2244篇 |
免费 | 92篇 |
国内免费 | 1篇 |
专业分类
林业 | 106篇 |
农学 | 50篇 |
基础科学 | 7篇 |
262篇 | |
综合类 | 700篇 |
农作物 | 87篇 |
水产渔业 | 141篇 |
畜牧兽医 | 756篇 |
园艺 | 62篇 |
植物保护 | 166篇 |
出版年
2023年 | 12篇 |
2022年 | 7篇 |
2021年 | 28篇 |
2020年 | 35篇 |
2019年 | 48篇 |
2018年 | 46篇 |
2017年 | 39篇 |
2016年 | 36篇 |
2015年 | 34篇 |
2014年 | 37篇 |
2013年 | 90篇 |
2012年 | 131篇 |
2011年 | 174篇 |
2010年 | 95篇 |
2009年 | 74篇 |
2008年 | 138篇 |
2007年 | 162篇 |
2006年 | 153篇 |
2005年 | 142篇 |
2004年 | 157篇 |
2003年 | 148篇 |
2002年 | 126篇 |
2001年 | 22篇 |
2000年 | 27篇 |
1999年 | 31篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1979年 | 8篇 |
1977年 | 6篇 |
1975年 | 7篇 |
1973年 | 6篇 |
1971年 | 6篇 |
1969年 | 7篇 |
1968年 | 5篇 |
1967年 | 10篇 |
1885年 | 5篇 |
排序方式: 共有2337条查询结果,搜索用时 31 毫秒
991.
Jeffrey G. Scott Cheryl A. Leichter Frank D. Rinkevihc Sarah A. Harris Cathy Su Lauren C. Aberegg Roger Moon Christopher J. Geden Alec C. Gerry David B. Taylor Ronnie L. Byford Wes Watson Gregory Johnson David Boxler Ludek Zurek 《Pesticide biochemistry and physiology》2013
Although insecticide resistance is a widespread problem for most insect pests, frequently the assessment of resistance occurs over a limited geographic range. Herein, we report the first widespread survey of insecticide resistance in the USA ever undertaken for the house fly, Musca domestica, a major pest in animal production facilities. The levels of resistance to six different insecticides were determined (using discriminating concentration bioassays) in 10 collections of house flies from dairies in nine different states. In addition, the frequencies of Vssc and CYP6D1 alleles that confer resistance to pyrethroid insecticides were determined for each fly population. Levels of resistance to the six insecticides varied among states and insecticides. Resistance to permethrin was highest overall and most consistent across the states. Resistance to methomyl was relatively consistent, with 65–91% survival in nine of the ten collections. In contrast, resistance to cyfluthrin and pyrethrins + piperonyl butoxide varied considerably (2.9–76% survival). Resistance to imidacloprid was overall modest and showed no signs of increasing relative to collections made in 2004, despite increasing use of this insecticide. The frequency of Vssc alleles that confer pyrethroid resistance was variable between locations. The highest frequencies of kdr, kdr-his and super-kdr were found in Minnesota, North Carolina and Kansas, respectively. In contrast, the New Mexico population had the highest frequency (0.67) of the susceptible allele. The implications of these results to resistance management and to the understanding of the evolution of insecticide resistance are discussed. 相似文献
992.
Maia Tsikolia Ulrich R. Bernier Monique R. Coy Katelyn C. Chalaire James J. Becnel Natasha M. Agramonte Nurhayat Tabanca David E. Wedge Gary G. Clark Kenneth J. Linthicum Daniel R. Swale Jeffrey R. Bloomquist 《Pesticide biochemistry and physiology》2013
Twenty trifluoromethylphenyl amides were synthesized and evaluated as fungicides and as mosquito toxicants and repellents. Against Aedes aegypti larvae, N-(2,6-dichloro-4-(trifluoromethyl)phenyl)-3,5-dinitrobenzamide (1e) was the most toxic compound (24 h LC50 1940 nM), while against adults N-(2,6-dichloro-4-(trifluoromethyl)phenyl)-2,2,2-trifluoroacetamide (1c) was most active (24 h LD50 19.182 nM, 0.5 μL/insect). However, the 24 h LC50 and LD50 values of fipronil against Ae. aegypti larvae and adults were significantly lower: 13.55 nM and 0.787 × 10−4 nM, respectively. Compound 1c was also active against Drosophila melanogaster adults with 24 h LC50 values of 5.6 and 4.9 μg/cm2 for the Oregon-R and 1675 strains, respectively. Fipronil had LC50 values of 0.004 and 0.017 μg/cm2 against the two strains of D. melanogaster, respectively. In repellency bioassays against female Ae. aegypti, 2,2,2-trifluoro-N-(2-(trifluoromethyl)phenyl)acetamide (4c) had the highest repellent potency with a minimum effective dosage (MED) of 0.039 μmol/cm2 compared to DEET (MED of 0.091 μmol/cm2). Compound N-(2-(trifluoromethyl)phenyl)hexanamide (4a) had an MED of 0.091 μmol/cm2 which was comparable to DEET. Compound 4c was the most potent fungicide against Phomopsis obscurans. Several trends were discerned between the structural configuration of these molecules and the effect of structural changes on toxicity and repellency. Para- or meta- trifluoromethylphenyl amides with an aromatic ring attached to the carbonyl carbon showed higher toxicity against Ae. aegypti larvae, than ortho- trifluoromethylphenyl amides. Ortho- trifluoromethylphenyl amides with trifluoromethyl or alkyl group attached to the carbonyl carbon produced higher repellent activity against female Ae. aegypti and Anopheles albimanus than meta- or para- trifluoromethylphenyl amides. The presence of 2,6-dichloro- substitution on the phenyl ring of the amide had an influence on larvicidal and repellent activity of para- trifluoromethylphenyl amides. 相似文献
993.
Laboratory experiments and field trials demonstrated that canola oil, which is rich in fatty acids that are kairomonal cues in cannibalism, is an effective attractant of rangeland grasshoppers and a suitable oil-based carrier for insecticides. Laboratory-based olfactory tests revealed a significant, positive chemotaxis of Melanoplus sanguinipes in response to canola oil and olive oil mixtures. Small-scale field tests made by airbrush applications of 5 ml of canola oil (equivalent to 500 l/ha) to centres of aluminium rings (0.1 m2 相似文献
994.
Designing relevant biochars as soil amendments using lignocellulosic-based and manure-based feedstocks 总被引:1,自引:0,他引:1
Jeffrey M. Novak Keri B. Cantrell Donald W. Watts Warren J. Busscher Mark G. Johnson 《Journal of Soils and Sediments》2014,14(2):330-343
Purpose
Biochars are a by-product of the biofuel processing of lignocellulosic and manure feedstocks. Because biochars contain an assemblage of organic and inorganic compounds, they can be used as an amendment for C sequestration and soil quality improvement. However, not all biochars are viable soil amendments; this is because their physical and chemical properties vary due to feedstock elemental composition, biofuel processing, and particle size differences. Biochar could deliver a more effective service as a soil amendment if its chemistry was designed ex ante with characteristics that target specific soil quality issues. In this study, we demonstrate how biochars can be designed with relevant properties as successful soil amendments through feedstock selection, pyrolysis conditions, and particle size choices.Materials and methods
Biochars were produced by pyrolysis of parent lignocellulosic feedstock sources—peanut hull (PH; Archis hypogaea), pecan shell (PS; Carya illinoensis), switchgrass (SG; Panicum virgatum), pine chips (PC; Pinus taeda), hardwood wastes (wood), and poultry litter manure (PL; Gallus domesticus), as well as blends of these feedstocks at temperatures ranging from 250 to 700 °C. Additionally, blended feedstocks were made into pellets (>2 mm) prior to pyrolysis at 350 °C. Dust-sized (<0.42 mm) biochar was obtained through grinding of pelletized biochars. After chemical characterization, the biochars were evaluated as fertility amendments in a Norfolk soil (fine-loamy, kaolinitic, thermic, Typic Kandiudult) during two different pot incubation experiments.Results and discussion
PL biochars were alkaline and enriched in N and P, whereas biochar from lignocellulosic feedstocks exhibited mixed pH and nutrient contents. Blending PL with PC resulted in lower biochar pH values and nutrient contents. In pot experiment 1, most biochars significantly (P?<?0.05) raised soil pH, soil organic carbon, cation exchange capacity, and Mehlich 1 extractable P and K. PL biochar added at 20 g?kg?1 resulted in excessive soil P concentrations (393 to 714 mg?kg?1) and leachate enriched with dissolved phosphorus (DP, 22 to 70 mg?L?1). In pot experiment 2, blended and pelletized PL with PC feedstock reduced soil pH and extractable soil P and K concentrations compared to pot experiment 1. Water leachate DP concentrations were significantly (P?<?0.05) reduced by pelletized biochar blends.Conclusions
Short-term laboratory pot experiments revealed that biochars can have different impacts at modifying soil quality characteristics. Keying on these results allowed for creating designer biochars to address specific soil quality limitations. In the process of manufacturing designer biochars, first, it is important to know what soil quality characteristics are in need of change. Second, choices between feedstocks, blends of these feedstocks, and their accompanying particle sizes can be made prior to pyrolysis to create biochars tailored for addressing specific soil quality improvements. Utilization of these principles should allow for effective service of the designed biochar as a soil amendment while minimizing unwanted ex facto soil quality changes and environmental effects. 相似文献995.
Alejandro M. S. Mayer Mary L. Hall Michael Holland Cristina De Castro Antonio Molinaro Monica Aldulescu Jeffrey Frenkel Lauren Ottenhoff David Rowley Jan Powell 《Marine drugs》2014,12(4):1732-1756
Although human exposure to Gram-negative Vibrio vulnificus (V. vulnificus) lipopolysaccharide (LPS) has been reported to result in septic shock, its impact on the central nervous system’s innate immunity remains undetermined. The purpose of this study was to determine whether V. vulnificus MO6-24/O LPS might activate rat microglia in vitro and stimulate the release of superoxide anion (O2−), a reactive oxygen species known to cause oxidative stress and neuronal injury in vivo. Brain microglia were isolated from neonatal rats, and then treated with either V. vulnificus MO6-24/O LPS or Escherichia coli O26:B6 LPS for 17 hours in vitro. O2− was determined by cytochrome C reduction, and matrix metalloproteinase-2 (MMP-2) and MMP-9 by gelatinase zymography. Generation of cytokines tumor necrosis factor alpha (TNF-α), interleukin-1 alpha (IL-1α), IL-6, and transforming growth factor-beta 1 (TGF-β1), chemokines macrophage inflammatory protein (MIP-1α)/chemokine (C-C motif) ligand 3 (CCL3), MIP-2/chemokine (C-X-C motif) ligand 2 (CXCL2), monocyte chemotactic protein-1 (MCP-1)/CCL2, and cytokine-induced neutrophil chemoattractant-2alpha/beta (CINC-2α/β)/CXCL3, and brain-derived neurotrophic factor (BDNF), were determined by specific immunoassays. Priming of rat microglia by V. vulnificus MO6-24/O LPS in vitro yielded a bell-shaped dose-response curve for PMA (phorbol 12-myristate 13-acetate)-stimulated O2− generation: (1) 0.1–1 ng/mL V. vulnificus LPS enhanced O2− generation significantly but with limited inflammatory mediator generation; (2) 10–100 ng/mL V. vulnificus LPS maximized O2− generation with concomitant release of thromboxane B2 (TXB2), matrix metalloproteinase-9 (MMP-9), and several cytokines and chemokines; (3) 1000–100,000 ng/mL V. vulnificus LPS, with the exception of TXB2, yielded both attenuated O2− production, and a progressive decrease in MMP-9, cytokines and chemokines investigated. Thus concentration-dependent treatment of neonatal brain microglia with V. vulnificus MO6-24/O LPS resulted in a significant rise in O2− production, followed by a progressive decrease in O2− release, with concomitant release of lactic dehydrogenase (LDH), and generation of TXB2, MMP-9, cytokines and chemokines. We hypothesize that the inflammatory mediators investigated may be cytotoxic to microglia in vitro, by an as yet undetermined autocrine mechanism. Although V. vulnificus LPS was less potent than E. coli LPS in vitro, inflammatory mediator release by the former was clearly more efficacious. Finally, we hypothesize that should V. vulnificus LPS gain entry into the CNS, it would be possible that microglia might become activated, resulting in high levels of O2− as well as neuroinflammatory TXB2, MMP-9, cytokines and chemokines. 相似文献
996.
Santosh Sanjel Martha Hincapie Yunwen Wang James Todd Bhim Chaulagain Sushma Sood Jack C. Comstock Richard N. Raid Philippe Rott 《Plant pathology》2021,70(7):1616-1625
Orange rust of sugarcane caused by Puccinia kuehnii was first reported in Florida in 2007. Since then, several sugarcane cultivars that were resistant during the initial epidemics became susceptible within a few years. These shifts in resistance were attributed to the evolution of the pathogen and appearance of new races. To study the variation in virulence of P. kuehnii, healthy leaf pieces of sugarcane cultivars susceptible to orange rust were brush inoculated with isolates of P. kuehnii collected from susceptible cultivars in the field. After inoculation, leaf pieces were placed in an incubator and disease severity based on the number of rust uredinia was determined 2 weeks postinoculation. Isolates of P. kuehnii collected from sugarcane cultivar CP 89-2143, which only showed severe symptoms of orange rust starting in 2011–2012, produced 300%–500% more uredinia on CP 89-2143 than the isolates collected from cultivar CL 85-1040 that has been susceptible since 2007. Sugarcane cultivar CL 85-1040 exhibited high and equivalent numbers of uredinia regardless of the inoculated isolate of the pathogen. These data support the occurrence of pathogenic specialization within P. kuehnii and the existence of at least two races of this pathogen in Florida. Analysis of amplified fragment-length polymorphism among isolates of P. kuehnii from cultivars CP 89-2143 and CL 85-1040 differing in resistance to orange rust revealed genetic variation among rust uredinia. However, this variation was not associated with a specific sugarcane cultivar, suggesting that pathogenic variation was not linked to major, but rather to small genetic changes within the genome of P. kuehnii. 相似文献
997.
Alexander Rodriguez-Palacios Tim Barman Jeffrey T. LeJeune 《The Canadian veterinary journal. La revue veterinaire canadienne》2014,55(8):786-789
The cross-sectional (period) prevalence of Clostridium difficile in 875 farm animals from 29 commercial operations during the summer of 2008 in Ohio, USA was quantified. Compared to an external referent population of intensively managed race horses (12.7%), intensively managed commercially mature food animals (poultry, cattle, swine; < 0.6%) were infrequent shedders of C. difficile (P < 0.00001) during the warmest weeks of 2008. 相似文献
998.
Erin N. Kishi Shannon P. Holmes Jeffrey R. Abbott Nicholas J. Bacon 《The Canadian veterinary journal. La revue veterinaire canadienne》2014,55(4):383-388
A 12-year-old dachshund dog was presented for persistent hypercalcemia and hyperparathyroidism despite bilateral parathyroidectomy. Magnetic resonance imaging of the head, neck, and cranial mediastinum identified an increased number of cranial mediastinal lymph nodes with heterogeneous signal intensity. Hypercalcemia and hyperparathyroidism resolved after surgery to remove multiple cranial mediastinal lymph nodes, one of which contained presumed metastatic parathyroid tissue. 相似文献
999.