全文获取类型
收费全文 | 9261篇 |
免费 | 430篇 |
国内免费 | 14篇 |
专业分类
林业 | 588篇 |
农学 | 229篇 |
基础科学 | 84篇 |
1586篇 | |
综合类 | 1611篇 |
农作物 | 366篇 |
水产渔业 | 822篇 |
畜牧兽医 | 3372篇 |
园艺 | 278篇 |
植物保护 | 769篇 |
出版年
2024年 | 19篇 |
2023年 | 59篇 |
2022年 | 90篇 |
2021年 | 155篇 |
2020年 | 212篇 |
2019年 | 208篇 |
2018年 | 206篇 |
2017年 | 218篇 |
2016年 | 210篇 |
2015年 | 184篇 |
2014年 | 252篇 |
2013年 | 450篇 |
2012年 | 542篇 |
2011年 | 707篇 |
2010年 | 368篇 |
2009年 | 352篇 |
2008年 | 635篇 |
2007年 | 623篇 |
2006年 | 592篇 |
2005年 | 574篇 |
2004年 | 608篇 |
2003年 | 571篇 |
2002年 | 504篇 |
2001年 | 98篇 |
2000年 | 90篇 |
1999年 | 93篇 |
1998年 | 81篇 |
1997年 | 70篇 |
1996年 | 67篇 |
1995年 | 62篇 |
1994年 | 61篇 |
1993年 | 50篇 |
1992年 | 57篇 |
1991年 | 49篇 |
1990年 | 58篇 |
1989年 | 49篇 |
1988年 | 42篇 |
1987年 | 44篇 |
1986年 | 33篇 |
1985年 | 32篇 |
1984年 | 34篇 |
1983年 | 40篇 |
1982年 | 26篇 |
1981年 | 25篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1974年 | 15篇 |
排序方式: 共有9705条查询结果,搜索用时 0 毫秒
81.
Comparison of antioxidant potency of commonly consumed polyphenol-rich beverages in the United States 总被引:4,自引:0,他引:4
Seeram NP Aviram M Zhang Y Henning SM Feng L Dreher M Heber D 《Journal of agricultural and food chemistry》2008,56(4):1415-1422
A number of different beverage products claim to have antioxidant potency due to their perceived high content of polyphenols. Basic and applied research indicates that pomegranate juice (PJ), produced from the Wonderful variety of Punica granatum fruits, has strong antioxidant activity and related health benefits. Although consumers are familiar with the concept of free radicals and antioxidants, they are often misled by claims of superior antioxidant activity of different beverages, which are usually based only on testing of a limited spectrum of antioxidant activities. There is no available direct comparison of PJ's antioxidant activity to those of other widely available polyphenol-rich beverage products using a comprehensive variety of antioxidant tests. The present study applied (1) four tests of antioxidant potency [Trolox equivalent antioxidant capacity (TEAC), total oxygen radical absorbance capacity (ORAC), free radical scavenging capacity by 2,2-diphenyl-1-picrylhydrazyl (DPPH), and ferric reducing antioxidant power (FRAP)]; (2) a test of antioxidant functionality, that is, inhibition of low-density lipoprotein (LDL) oxidation by peroxides and malondialdehyde methods; and (3) evaluation of the total polyphenol content [by gallic acid equivalents (GAEs)] of polyphenol-rich beverages in the marketplace. The beverages included several different brands as follows: apple juice (3), a?aí juice (3), black cherry juice (3), blueberry juice (3), cranberry juice (3), Concord grape juice (3), orange juice (3), red wines (3), iced tea beverages (10) [black tea (3), green tea (4), white tea (3)], and a major PJ available in the U.S. market. An overall antioxidant potency composite index was calculated by assigning each test equal weight. PJ had the greatest antioxidant potency composite index among the beverages tested and was at least 20% greater than any of the other beverages tested. Antioxidant potency, ability to inhibit LDL oxidation, and total polyphenol content were consistent in classifying the antioxidant capacity of the polyphenol-rich beverages in the following order: PJ>red wine>Concord grape juice>blueberry juice>black cherry juice, a?aí juice, cranberry juice>orange juice, iced tea beverages, apple juice. Although in vitro antioxidant potency does not prove in vivo biological activity, there is also consistent clinical evidence of antioxidant potency for the most potent beverages including both PJ and red wine. 相似文献
82.
Ryan A. Davis David Huggins R. James Cook Timothy C. Paulitz 《Soil & Tillage Research》2008,101(1-2):37-43
Rhizoctonia root rot of wheat can be a problem in no-till systems, especially during the transition from conventional tillage. There are no effective chemical controls or resistant varieties, leaving only cultural methods to manage this disease. In a no-till system, residue and inoculum of soilborne pathogens are not moved by cultivation, therefore the inoculum may be concentrated in the seeding row of the previous year. Using GPS tracking systems with sub-meter accuracy, the seeding row could be placed away from the row of the previous year. We tested the hypothesis that seeding away from the relic row may reduce Rhizoctonia root rot. In two field experiments, plants were sampled at three distances from the seed row, as well as from fumigated plots. Intact soil cores were also removed from the field, planted with seeds at various distances from the previous row, and grown in the greenhouse under controlled conditions. Pasteurized cores served as controls. Disease levels were higher in the field in the second year, but there was no consistent effect of seed row placement on disease or plant parameters. However, soil fumigation and pasteurization had significant effects, indicating that soilborne pathogens were active. Inoculum of Rhizoctonia is not produced in the crowns and lower stems of the plant, but the pathogen survives in living and dead roots of the previous year crop, volunteers, and grassy weeds. Thus, high inoculum densities may be present in between the relic rows, as well as within the rows. If this is the situation with Rhizoctonia, precision placement of seed rows would not be efficacious. 相似文献
83.
Michael Simone-Finstrom Micheline K Strand David R Tarpy Olav Rueppell 《Journal of insect science (Online)》2022,22(1)
The effects of honey bee management, such as intensive migratory beekeeping, are part of the ongoing debate concerning causes of colony health problems. Even though comparisons of disease and pathogen loads among differently managed colonies indicate some effects, the direct impact of migratory practices on honey bee pathogens is poorly understood. To test long- and short-term impacts of managed migration on pathogen loads and immunity, experimental honey bee colonies were maintained with or without migratory movement. Individuals that experienced migration as juveniles (e.g., larval and pupal development), as adults, or both were compared to control colonies that remained stationary and therefore did not experience migratory relocation. Samples at different ages and life-history stages (hive bees or foragers), taken at the beginning and end of the active season, were analyzed for pathogen loads and physiological markers of health. Bees exposed to migratory management during adulthood had increased levels of the AKI virus complex (Acute bee paralysis, Kashmir bee, and Israeli acute bee paralysis viruses) and decreased levels of antiviral gene expression (dicer-like). However, those in stationary management as adults had elevated gut parasites (i.e. trypanosomes). Effects of environment during juvenile development were more complex and interacted with life-history stage and season. Age at collection, life-history stage, and season all influenced numerous factors from viral load to immune gene expression. Although the factors that we examined are not independent, the results illuminate potential factors in both migratory and nonmigratory beekeeping that are likely to contribute to colony stress, and also indicate potential mitigation measures. 相似文献
84.
David L. Renaud Natalia Savor Jessica Gordon David F. Kelton Cynthia Miltenburg 《The Canadian veterinary journal. La revue veterinaire canadienne》2022,63(3):297
The objective of this cross-sectional study was to evaluate the presence of infectious disease in newly arrived cattle on dairy farms in Ontario. Cattle that were more than 2 years old and arrived at dairy farms within the previous year were tested. A total 321 cattle from 56 dairy farms were sampled and had blood submitted to a diagnostic laboratory. Of all sampled cattle, 0.0%, 39.6%, 2.2%, and 1.3% tested positive for Anaplasma, bovine leukemia virus, Mycobacterium avium subsp. paratuberculosis, and Salmonella Dublin, respectively. Based on these results, it is imperative that dairy producers are vigilant to ensure they do not purchase animals with these important and untreatable infectious diseases. 相似文献
85.
86.
Glyphosate was recently evaluated for its potential to interact with the estrogen, androgen and thyroid (EAT) hormone pathways, including steroidogenesis, under the United States Environmental Protection Agency's (USEPA) Endocrine Disruptor Screening Program (EDSP), then by Germany, the rapporteur Member State who led the European Annex 1 renewal for glyphosate, and then by the European Food Protection Agency (EFSA) also as part of the Annex 1 renewal for glyphosate. Under the EDSP, 11 Tier 1 assays were run following the USEPA's validated 890‐series test guidelines and included five in vitro and six in vivo assays to evaluate the EAT pathways. Steroidogenesis was evaluated as part of the estrogen and androgen pathways. An up‐to‐date critical review has been conducted that considered results from the EDSP Tier 1 battery, guideline regulatory studies and an in‐depth analysis of the literature studies that informed an endocrine assessment. A strength of this evaluation was that it included data across multiple levels of biological organization, and mammalian and nonmammalian test systems. There was strong agreement across the in vitro and in vivo Tier 1 battery, guideline studies and relevant literature studies, demonstrating that glyphosate does not interact with EAT pathways including steroidogenesis. Based on an analysis of the comprehensive toxicology database for glyphosate and the literature, this review has concluded that glyphosate does not have endocrine‐disrupting properties through estrogen, androgen, thyroid and steroidogenic modes of action. © 2020 Society of Chemical Industry 相似文献
87.
88.
89.
Řebíčková Kristýna Bajer Tomáš Šilha David Ventura Karel Bajerová Petra 《Plant foods for human nutrition (Dordrecht, Netherlands)》2020,75(4):495-504
Plant Foods for Human Nutrition - The purpose of this study was to compare the yield, chemical composition, antimicrobial and antioxidant properties of essential oils isolated from leaves of Laurus... 相似文献
90.