全文获取类型
收费全文 | 1825篇 |
免费 | 67篇 |
国内免费 | 80篇 |
专业分类
林业 | 42篇 |
农学 | 173篇 |
基础科学 | 94篇 |
179篇 | |
综合类 | 1089篇 |
农作物 | 104篇 |
水产渔业 | 77篇 |
畜牧兽医 | 168篇 |
园艺 | 28篇 |
植物保护 | 18篇 |
出版年
2024年 | 7篇 |
2023年 | 18篇 |
2022年 | 58篇 |
2021年 | 48篇 |
2020年 | 43篇 |
2019年 | 46篇 |
2018年 | 17篇 |
2017年 | 70篇 |
2016年 | 72篇 |
2015年 | 105篇 |
2014年 | 118篇 |
2013年 | 125篇 |
2012年 | 151篇 |
2011年 | 151篇 |
2010年 | 115篇 |
2009年 | 135篇 |
2008年 | 108篇 |
2007年 | 98篇 |
2006年 | 85篇 |
2005年 | 67篇 |
2004年 | 37篇 |
2003年 | 55篇 |
2002年 | 26篇 |
2001年 | 23篇 |
2000年 | 23篇 |
1999年 | 26篇 |
1998年 | 16篇 |
1997年 | 19篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 17篇 |
1993年 | 13篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有1972条查询结果,搜索用时 671 毫秒
151.
Cary Fowler 《Genetic Resources and Crop Evolution》2004,51(6):609-620
The International Treaty on Plant Genetic Resources for Food and Agriculture is rapidly gathering sufficient ratifications to become international law. Once it enters into force, it will define the rules for access and benefit-sharing associated with most genetic resources of major food crops. This paper explains how the new Multilateral System established by the Treaty will work, and points out a number of ambiguities and problems in the text. Despite these shortcomings, the Treaty provides the international community of researchers, plant breeders, and farmers with an opportunity to foster cooperation and further the conservation and use of plant genetic resources. 相似文献
152.
153.
Soil food webs are mainly based on three primary carbon (C) sources: root exudates, litter, and recalcitrant soil organic matter (SOM). These C sources vary in their availability and accessibility to soil organisms, which could lead to different pathways in soil food webs. The presence of three C isotopes (12C, 13C and 14C) offers an unique opportunity to investigate all three C sources simultaneously. In a microcosm experiment we studied the effect of food web complexity on the utilization of the three carbon sources. We choose an incomplete three factorial design with (i) living plants, (ii) litter and (iii) food web complexity. The most complex food web consisted of autochthonous microorganisms, nematodes, collembola, predatory mites, endogeic and anecic earthworms. We traced C from all three sources in soil, in CO2 efflux and in individual organism groups by using maize grown on soil developed under C3 vegetation and application of 14C labelled ryegrass shoots as a litter layer. The presence of living plants had a much greater effect on C pathways than food web complexity. Litter decomposition, measured as 14CO2 efflux, was decreased in the presence of living plants from 71% to 33%. However, living plants increased the incorporation of litter C into microbial biomass and arrested carbon in the litter layer and in the upper soil layer. The only significant effect of food web complexity was on the litter C distribution in the soil layers. In treatments with fungivorous microarthropods (Collembola) the incorporation of litter carbon into mineral soil was reduced. Root exudates as C source were passed through rhizosphere microorganisms to the predator level (at least to the third trophic level). We conclude that living plants strongly affected C flows, directly by being a source of additional C, and indirectly by modifying the existing C flows within the food web including CO2 efflux from the soil and litter decomposition. 相似文献
154.
农用化学品及废弃物对土壤环境与食物安全的影响 总被引:5,自引:0,他引:5
综述了农用化学品和废弃物(化肥、农药、酸沉降、污水污泥、畜禽粪便和“三废”等)利用现状及其对土壤环境污染与食物安全的影响。 相似文献
155.
Impacts of population growth, economic development, and technical change on global food production and consumption 总被引:3,自引:0,他引:3
Uwe A. Schneider Petr HavlíkErwin Schmid Hugo ValinAline Mosnier Michael ObersteinerHannes Böttcher Rastislav SkalskýJuraj Balkovi? Timm SauerSteffen Fritz 《Agricultural Systems》2011,104(2):204-215
Over the next decades mankind will demand more food from fewer land and water resources. This study quantifies the food production impacts of four alternative development scenarios from the Millennium Ecosystem Assessment and the Special Report on Emission Scenarios. Partially and jointly considered are land and water supply impacts from population growth, and technical change, as well as forest and agricultural commodity demand shifts from population growth and economic development. The income impacts on food demand are computed with dynamic elasticities. Simulations with a global, partial equilibrium model of the agricultural and forest sectors show that per capita food levels increase in all examined development scenarios with minor impacts on food prices. Global agricultural land increases by up to 14% between 2010 and 2030. Deforestation restrictions strongly impact the price of land and water resources but have little consequences for the global level of food production and food prices. While projected income changes have the highest partial impact on per capita food consumption levels, population growth leads to the highest increase in total food production. The impact of technical change is amplified or mitigated by adaptations of land management intensities. 相似文献
156.
157.
将“六五”和“七五”期间各省、市初步选出的优异种质,包括单一性状和综合性状优异的种质资源,在“八五”期间进行再评价。安徽试点承担小豆优异种质产量鉴定、豇豆优异种质产量鉴定和豇豆优异种质资源观察鉴定圃等三项试验。经田间试验和统计分析,初步选出7—8个产量高、综合性状优良的小豆和豇豆品种,还选出一批具有矮生、早熟、大粒、多荚、蛋白质含量高的单项性状优良的种质资源,供育种、生物科学和生产上利用。 相似文献
158.
159.
160.