全文获取类型
收费全文 | 2302篇 |
免费 | 119篇 |
国内免费 | 219篇 |
专业分类
林业 | 125篇 |
农学 | 191篇 |
基础科学 | 208篇 |
501篇 | |
综合类 | 1257篇 |
农作物 | 51篇 |
水产渔业 | 93篇 |
畜牧兽医 | 148篇 |
园艺 | 24篇 |
植物保护 | 42篇 |
出版年
2024年 | 13篇 |
2023年 | 24篇 |
2022年 | 44篇 |
2021年 | 60篇 |
2020年 | 62篇 |
2019年 | 67篇 |
2018年 | 52篇 |
2017年 | 93篇 |
2016年 | 111篇 |
2015年 | 108篇 |
2014年 | 140篇 |
2013年 | 170篇 |
2012年 | 260篇 |
2011年 | 200篇 |
2010年 | 180篇 |
2009年 | 149篇 |
2008年 | 120篇 |
2007年 | 140篇 |
2006年 | 142篇 |
2005年 | 97篇 |
2004年 | 77篇 |
2003年 | 56篇 |
2002年 | 68篇 |
2001年 | 36篇 |
2000年 | 37篇 |
1999年 | 32篇 |
1998年 | 20篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1984年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有2640条查询结果,搜索用时 269 毫秒
101.
目前我国水产养殖废水直接排放的现象较多, 使受纳水体富营养化和生物多样性降低; 同时养殖水体中残饵、水生生物排泄物容易引起水体溶解氧下降、病原体增加并产生有害物质如氨氮、亚硝酸盐等, 引起养殖对象发病甚至死亡。提出采用以组合填料为载体的序批式生物膜反应器处理水产养殖废水。通过试验确定了最佳运行模式: 水力停留时间12 h, 其中瞬时进水y 厌氧( 3 h) y 曝气( 5 h) y 添加原水(添加比1B 3) y 缺氧( 3 h) y 曝气( 1 h) y 沉淀( 0. 5 h) y 排水( 0. 5 h), 并考察了试验对污染物的去除特性。试验结果表明了序批式生物膜法处理水产养殖废水的可行性, 对有机物、氨氮、TN、TP的平均去除率分别为91. 1%、85. 1%、751 8%、89. 5%, 处理后出水可回用于水产养殖。 相似文献
102.
《Communications in Soil Science and Plant Analysis》2012,43(19-20):2641-2655
Abstract Superferrite is marketed as a turf fertilizer in the United States, but there is limited information on its effectiveness or potential risks due to high zinc (Zn) and lead (Pb) contents. A greenhouse study was conducted where hybrid bermudagrass and tall fescue, growing in a calcareous clay or acid sandy soil, and creeping bentgrass, growing in a putting green root zone mix, were fertilized with 0, 50, 100, and 150% the recommended rate of Superferrite fertilizer (73.4 g m?2). Bermudagrass and tall fescue clipping weights increased with Superferrite rate but root mass was not affected. Tissue iron (Fe) concentrations were mostly unaffected by Superferrite, but total Fe uptake, tissue Zn, and total Zn uptake increased with Superferrite rate. Increased yields were probably due to increasing nitrogen (N) applications rather than Fe or Zn. Small increases in Pb uptake with Superferrite applications suggest that Superferrite Pb had low bioavailability to turf. 相似文献
103.
对菊花加工厂废水中的化学污染物和物理性状进行了检测,并在实验室内采用粉末炭活性污泥法对废水进行小规模处理。在实验条件下,BOD5去除率达93%,CODcr去除率为87%,总氮去除率为47%,总磷去除率为40%〈总硬度降低52%,出水的色度,悬浮物,PH等均达到排放标准。 相似文献
104.
105.
《Land Degradation \u0026amp; Development》2017,28(8):2432-2445
We combine high‐resolution soil sampling with lead (Pb) analyses (concentrations and stable isotopes) in two temperate podzols, together with previous data obtained with selective Al and Fe dissolution techniques. We aim to assess how atmospheric Pb is incorporated into the soils during pedogenesis. Partial least squares modelling for Pb concentrations shows that the podzolization process has the largest effect on Pb concentration (80·3% of the variance). The proportion of inorganic secondary compounds, the input of fresh organic matter from the soil surface and the relative abundance of Fe versus Al are responsible for a small part of the Pb concentration variance. Lead isotopic composition (206Pb/207Pb ratios) depends on soil organic matter content either fresh/poorly humified (57·3% of the variance) or humified (24·7% of the variance). The Pb linked to inorganic compounds and the overall podzolization process play a minor role in isotopic signature (5·3 and 3·7% of the variance respectively). Soil pH appears to be the controlling variable of the different transport and retention mechanisms. The relatively low isotopic ratios observed in spodic horizons result from geogenic Pb released through the preferential dissolution of the isotopically distinct most weatherable minerals of the parent material in the eluvial horizons, which undergoes downward mobilization. An accurate knowledge of soil reactive components and formation mechanisms is essential to a correct diagnose of the scope of Pb pollution and a more effective design of remediation strategies. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
106.
107.
108.
109.
Coke oven waste water is respectively pretreated by blast furnace sludge method and blast furnace sludge plus iron scrap method, the effects of pH and the quantity of materials and treatment time on the removal efficiency of COD are analyzed. The results indicate that blast furnace sludge plus iron scrap method is superior to blast furnace sludge method .The treatment time and pH can greatly affect on the removal efficiency of COD using blast furnace sludge plus iron scrap method. The treatment time after 30 minutes and pH have no remarkable effects the removal efficiency of COD using blast furnace sludge method. The removal efficiency of COD increases with the increase of blast furnace sludge and iron scrap, but the increase rate decreases gradually. 相似文献
110.