全文获取类型
收费全文 | 1816篇 |
免费 | 69篇 |
国内免费 | 90篇 |
专业分类
林业 | 312篇 |
农学 | 192篇 |
基础科学 | 89篇 |
197篇 | |
综合类 | 790篇 |
农作物 | 53篇 |
水产渔业 | 9篇 |
畜牧兽医 | 39篇 |
园艺 | 229篇 |
植物保护 | 65篇 |
出版年
2024年 | 12篇 |
2023年 | 23篇 |
2022年 | 50篇 |
2021年 | 51篇 |
2020年 | 54篇 |
2019年 | 70篇 |
2018年 | 40篇 |
2017年 | 63篇 |
2016年 | 76篇 |
2015年 | 82篇 |
2014年 | 101篇 |
2013年 | 120篇 |
2012年 | 190篇 |
2011年 | 160篇 |
2010年 | 124篇 |
2009年 | 128篇 |
2008年 | 102篇 |
2007年 | 80篇 |
2006年 | 74篇 |
2005年 | 51篇 |
2004年 | 48篇 |
2003年 | 47篇 |
2002年 | 25篇 |
2001年 | 22篇 |
2000年 | 21篇 |
1999年 | 20篇 |
1998年 | 17篇 |
1997年 | 20篇 |
1996年 | 31篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有1975条查询结果,搜索用时 0 毫秒
971.
《Land Degradation u0026amp; Development》2017,28(7):1933-1942
Due to the severe degradation of wetland ecosystems in China, great efforts, such as the reconstruction of forested wetlands, have been devoted to restore the damaged and degraded wetlands to support species diversity and ecosystem services. However, less attention has been given to the diversity and ecological significance of prokaryotes of the domain Archaea compared with prokaryotes of the domain Bacteria during the reconstruction of forested wetlands. Here, the effects of introduced woody plants (Taxodium distichum and Alnus trabeculosa ) on the archaeal community in a freshwater wetland in the Yangtze estuary were investigated. The results showed that Thaumarchaeota obviously predominated at three studied sites in the freshwater wetland, the relative abundance of which decreased with increasing depth, ranging from 93.9% (0–10 cm) to 1.9% (30–40 cm) in mudflats, from 100% (0–10 cm) to 64.8% (30–40 cm) in T. distichum sediment and from 100% (0–10 cm) to 66.7% (40–50 cm) in A. trabeculosa sediment. The abundances of the archaeal amoA gene in woody plant sediments, ranging from 3.27 × 107 to 2.45 × 108 copies g−1 dry soil, were significantly higher than those in bare mudflat, ranging from 9.23 × 106 to 1.35 × 107 copies g−1 dry soil. The archaeal community, which was significantly affected by pH, microbial carbon and SO42− contents according to a canonical correspondence analysis, was significantly altered by plants and soil depth (p < 0.05). These results indicated that the introduction of woody plants stimulates the proliferation of Thaumarchaeota, especially ammonia‐oxidizing archaea, which could be important contributors to the N cycle in forested wetland ecosystems. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
972.
本文调查分析了江西省余江县39个大型养猪场的饲料、猪粪、以及长期施用这些猪粪的菜地土壤及蔬菜的Cu、Zn、Pb、Cd含量,并对饲料、猪粪、土壤和蔬菜重金属含量进行了相关分析。结果表明,大猪和小猪饲料Cu含量超标率分别达81.6%和30.8%,Zn含量超标率分别达89.5%和94.9%,而Pb、Cd未超标。猪粪Cu、Zn含量亦严重超标,且饲料和猪粪中Cu、Zn、Pb、Cd含量呈显著正相关关系。土壤总Zn和总Cd含量分别有7.8%和5.2%的样品超过三级标准,污染较为严重。所有蔬菜样品Cu、Zn、Pb含量均未超过我国食品卫生质量标准,空心菜和芋头Cd含量超标。土壤总Cu、Zn、Cd含量与提取态呈显著正相关。 相似文献
973.
Ethnic vegetable crops are increasingly being grown in the United States and may accumulate heavy metals when grown on urban soils. This study evaluated accumulation of lead (Pb) and arsenic (As) in tissues of Malabar spinach (Basella alba L.) and sweet potato (Ipomoea batatas L.) grown on an urban and an orchard soil with Pb concentrations of 1,120 and 272 mg kg?1, respectively, and As concentrations of 6.92 and 90 mg kg?1, respectively. Tissue Pb was higher in both crops grown on both contaminated soils compared with an uncontaminated soil, while tissue As was higher on the orchard soil only. Malabar spinach did not accumulate Pb or As in its shoot, but concentrations of both metals were higher in sweet potato stems compared to leaves or tubers. Consumption of sweet potato stems should be avoided when sweet potato leaves are grown as a vegetable on soils with elevated levels of Pb and As. 相似文献
974.
Jolanta Franczuk Edyta Kosterna Anna Zaniewicz-Bajkowska 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(5):472-479
Abstract A field experiment was conducted during the period 2002–2006 at the Experimental Farm in Zawady, located in the mid-eastern part of Poland, to evaluate the effect of date of mulch ploughing down (autumn, spring, left till cabbage harvest) and the plant mulches [phacelia (Phacelia tanacetifolia Benth.), vetch (Vicia sativa L.), serradella (Ornithopus sativus), and oat (Avena sativa L.)] on the weed pressure in red cabbage (Brassica oleracea L. var. capitata L. f. rubra) in the first and onion (Allium cepa L. var. cepa Helm.) in the second year after mulching. The biomass yield of plant mulches, total cabbage and onion yields, and biomass and number of weeds before planting and harvest of cabbage and before sowing and harvest of onion were assessed. Weed infestation was determined by the quantitative-weighting method. The biomass yields of phacelia and oat amounted to 26.6 and 24.8 t·ha?1, respectively, and were almost 2.5-times higher than biomass yields of serradella and vetch. The average cabbage and onion yields were 45.8 and 41.9 t·ha?1, respectively. The yields of vegetables following mulches were higher than the yields recorded in the unmulched control. The weed species most often found in the experiment were Viola arvensis Murr., Capsella bursa pastoris, Matricaria indora L., Chenopodium album L., and Stellaria media (L.) Vill. Of the examined dates of mulch ploughing down, the spring-incorporated mulches were most effective in reducing the number of weeds in cabbage whereas the nonincorporated mulches showed such an effect in onion. Nonlegumes (phacelia and oat) used as mulch produced higher fresh biomass yields than did vetch and serradella. Oat and phacelia mulches significantly reduced the fresh biomass and number of weeds before cabbage planting. Additionally, oat mulch reduced the fresh biomass of weeds before cabbage harvest. Also, oat and phacelia mulches reduced the number of weeds before onion harvest. 相似文献
975.
J. Gebauer K. El-Siddig B. A. El Tahir A. A. Salih G. Ebert K. Hammer 《Genetic Resources and Crop Evolution》2007,54(8):1701-1708
The small leaved white cross berry (Grewia tenax [Forssk.] Fiori) is a fruit-producing deciduous shrub or small tree of widespread occurrence in semi-arid and sub-humid tropical
climates. Despite its well-recognized potential and high prices on local markets, there are no commercial plantations in Sudan.
Wild plants have continuously been used to meet the growing commercial demand for their fruits. Recently, there has been an
increased interest in finding alternative, potentially high-value cash crops to improve the income of small farmers who are
currently depending upon growing and selling millet (Pennisetum glaucum [L.] R. Br.), sorghum (Sorghum bicolor [L.] Moench), sesame (Sesamum indicum L.), and groundnut (Arachis hypogaea L.). G. tenax has often been cited as a prime candidate for domestication as a useful horticultural plant. One major factor hampering this
development is the limited and scattered knowledge available on this species. The purpose of this paper is to highlight the
importance of G. tenax by providing information on its botanical and horticultural characteristics in the effort to promote its domestication and
commercialization for regional and global markets. 相似文献
976.
湖北省蔬菜产销现状是供大于求,存在小生产与大市场大流通的矛盾日益加剧,蔬菜品质亟待提高,蔬菜产品加工增值环节薄弱等问题,湖北省应结合省情、国情进行全面规划,制定蔬菜生产可持续发展战略。要统筹安排,搞好蔬菜基地布局,推进蔬菜产业化发展;要建立完善的蔬菜产销体系;提高农民素质,实施科技兴菜;要推广无公害蔬菜生产技术,以优质蔬菜占领市场;提高加工转化能力,促进蔬菜增值。 相似文献
977.
978.
979.
980.
据调查,鄱阳湖野生蔬菜有25种,分16科24属。根据对湖水深度和草洲土壤湿度等适应性的差异,将其生境类型分为水生野生蔬菜有浮叶型、挺水型,旱生野生蔬菜有湿生型和中生型。浮叶型主要分布于高程11~13m的湖底滩地上,叶片浮水而生;挺水型分布高程12~15m,植株挺立水面生长;湿生型和中生型则主要分布于高程14~17m的草洲。鄱阳湖野生蔬菜种类随湖水的涨落呈季节性更替,且多呈不规则等高分布。 相似文献