首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1491篇
  免费   70篇
  国内免费   183篇
林业   95篇
农学   127篇
基础科学   189篇
  318篇
综合类   846篇
农作物   18篇
水产渔业   69篇
畜牧兽医   56篇
园艺   7篇
植物保护   19篇
  2024年   12篇
  2023年   13篇
  2022年   27篇
  2021年   35篇
  2020年   40篇
  2019年   37篇
  2018年   25篇
  2017年   62篇
  2016年   56篇
  2015年   70篇
  2014年   96篇
  2013年   118篇
  2012年   157篇
  2011年   139篇
  2010年   116篇
  2009年   108篇
  2008年   86篇
  2007年   104篇
  2006年   110篇
  2005年   68篇
  2004年   51篇
  2003年   36篇
  2002年   47篇
  2001年   23篇
  2000年   25篇
  1999年   26篇
  1998年   13篇
  1997年   8篇
  1996年   5篇
  1995年   10篇
  1994年   9篇
  1993年   2篇
  1992年   1篇
  1991年   3篇
  1990年   1篇
  1989年   4篇
  1988年   1篇
排序方式: 共有1744条查询结果,搜索用时 15 毫秒
161.
粉煤灰处理含氟废水单因素实验研究   总被引:2,自引:0,他引:2  
为处理含氟废水,本实验采用粉煤灰作为吸附材料,并进行了影响粉煤灰处理含氟废水的各种单因素条件下的实验.结果表明最佳处理条件是pH值为3,水灰比小于11:1,振荡时间为135min,氟浓度小于400mg/L.在此条件下对400mg/L的含氟废水可达到94%以上的去除率.粉煤灰对处置含氟废水是一个很好的吸附材料,但除氟后饱和灰的处置也应引起重视.  相似文献   
162.
畜禽废水胁迫对芦苇叶绿素含量及抗氧化酶系统的影响   总被引:11,自引:0,他引:11  
采用自然条件模拟实验,以两种浓度畜禽废水(高浓度畜禽废水原水和经一倍稀释的中浓度畜禽废水)胁迫湿地植物芦苇,研究其对芦苇叶绿素含量及其抗氧化酶系统的影响。结果表明,高浓度畜禽废水较中浓度畜禽废水对芦苇的影响更大。两种浓度畜禽废水胁迫均促使芦苇叶绿素含量下降、叶绿素a/b值上升、CAT活性下降、POD活性急速下降后逐渐上升,到处理末期时与对照基本相同、SOD活性明显上升。说明畜禽废水胁迫对芦苇的影响较小,芦苇在畜禽废水胁迫下具有较强的抗逆性和耐受性.如果将其运用于我国集约化畜禽养殖业废水的处理,将极大地缓解我国畜禽养殖业发展与环境污染之间的矛盾。  相似文献   
163.
In many nurseries in the Mediterranean area irrigation water supply is a major problem due to climatic conditions, and it is important to evaluate alternative water resources, such as treated wastewater, for ornamental plant production. For this reason, a nursery study was conducted in order to determine: (1) the effect of irrigation with a saline reclaimed wastewater (reused water) on the growth and visual quality of Lantana camara and Polygala myrtifolia, and (2) the effectiveness of the mixing the same water with canal water to reduce any negative effects observed with the reused water. Potted plants were irrigated with reused water, canal water and reused water diluted 50% with canal water. The results suggest that polygala can be irrigated with reused water since visual damage is minimal and growth reduction very slight, which seems to be related with the plant's low accumulation of saline ions. In lantana, reused water led to an excessive uptake of chloride, sodium and boron in the leaves, which was associated with defoliation, leaf burn, leaf chlorosis and damage to the photosynthetic apparatus, diminishing both growth and its aesthetic value. The dilution of reused water alleviated some negative effects in lantana, but not sufficiently to avoid a significant loss of plant quality.  相似文献   
164.
The purpose of this study was to evaluate the physico-chemical characteristics and the post-harvest loss of mass of curly lettuce (Lactuca sativa L.) cv. Verônica that was grown in a protective environment with applications of biopesticides. The curly lettuce was treated by spraying with neem oil, cassava flour wastewater (manipueira), biofertiliser or the control treatment of deltamethrin. We determined the weight, circumference, dry matter, ash, crude protein, total phenols and minerals profile for the heads of lettuce. After harvesting, the lettuce was packed into opened plastic bags and kept at 5 °C for 5 days to evaluate its weight loss. No differences were observed among the treatments for the physico-chemical parameters. The lettuce that was sprayed with manipueira or biofertiliser had the greatest weight loss during storage. The achievement of similar yields with cheaper products suggests a benefit of using organic bioinsecticides.  相似文献   
165.
The scarcity of freshwater resources is a critical problem in semi-arid zones and marginal quality water is increasingly being used in agriculture. This paper aimed at evaluating the physico-chemical and biological risks on irrigated soils and fruits of macrophyte treated wastewater (TWW), the nutrients supply, and the effect on tomato and eggplant production in semi-arid Burkina Faso. During three years of experiments, treated wastewater was used, with fresh water as control, in combination with or without mineral fertilizer application at recommended rate (140 kg N/ha + 180 kg P2O5/ha + 180 kg K2O/ha). The study revealed that the treated wastewater provided variable nutrients supply depending on year and element. The treated wastewater without mineral fertilizer improved eggplant yield (40% in average) compared to the freshwater. Both crops responded better to mineral fertilizer (52% for tomato and 82% for eggplant) and the effects of the treated wastewater and fertilizer were additive. As the N supply of TWW was very unsteady (8-227% of crop need), and P2O5 supply did not satisfy in whole crop need (3-58%) during any of the three years of experiment, we recommended that moderate N and P2O5 fertilizers be applied when irrigating with TWW in semi-arid West-Africa. On the contrary, the K2O supply was more steady and close to crop requirement (78-126%) over the three years of experiment and no addition of K fertilizer may be needed when irrigated with TWW. Faecal coliforms and helminth eggs were observed in treated wastewater and irrigated soils at rate over the FAO and WHO recommended limits for vegetable to be eaten uncooked. Tomato fruits were observed to be faecal coliform contaminated with the direct on-foliage irrigation with treated wastewater. Our results indicate that treated wastewater can effectively be used as both nutrients source and crop water supply in market gardening in the semi-arid Sub-Saharan West Africa (SSWA) where freshwater and farm income are limiting. Yet consumers should properly cook or disinfect treated-wastewater irrigated vegetables before eating, and market gardeners should also be careful manipulating treated wastewater to avoid direct health contamination in this environment.  相似文献   
166.
氧化塘深度对猪场厌氧消化液后处理的影响   总被引:1,自引:0,他引:1  
采用小试装置对3个不同深度氧化塘处理猪场厌氧消化液的效果进行了研究,结果表明:当平均气温为21.9℃,停留时间在80 ~110天,进水负荷为0.05 m3·m-2d-1的条件下,氧化塘对NH4-N的去除率达到了90%以上,CODcr,TP的去除率分别为50%,40%.硝化作用和藻类的吸收是氧化塘去除NH4-N的主要方式,沉淀作用则是CODcr和TP的主要去除方式,在较长停留时间下,微生物对于溶解性CODcr的分解和同化也能提供一定的去除效果.当平均气温为21.9℃,在表面负荷为0.05 m3·m-2d-1的条件下,有效深度为0.3m和0.7m的氧化塘面积去除负荷分别为1.41 g·m-2d-1,1.49 g·m-2d-1,容积去除负荷分别为4.7g·m -3d-1,2.8g·m-3d-1.虽然较深氧化塘具有较高的面积去除负荷,但较浅的氧化塘却有更高的容积去除负荷.  相似文献   
167.
稻田对池塘养殖肥水的吸收利用效果研究   总被引:3,自引:0,他引:3  
池塘养殖废水由于富含氮、磷等营养物质,故有时又称其为养殖肥水。为了实现养殖废水零排放的目标,进行了池塘养殖水灌溉稻田的试验。结果表明,①稻田对来自养殖池塘的灌溉水中的营养物质具有明显的吸收效果,尤其对NO3--N和TP。池塘养殖水在田间滞留8h以上,就有一定吸收效果:对TN、TP、NO3--N、NH4+-N和CODMn...  相似文献   
168.
选择一种新型高效反应器系统对奶牛养殖场废水进行处理试验研究,这种反应器系统主要包括两级组合生物巢厌氧反应器和砂式沼液处理池。试验结果表明,该系统处理奶牛养殖废水速度快,两级组合生物巢厌氧反应器水力停留时间(HRT)仅为15h,处理效率高,砂式沼液处理池结构简单,对生物巢厌氧反应器出水处理效果好。该新型高效反应器组合系统对化学需氧量(COD)、生化需氧量(BOD)、氨氮(NH3-N)和总固体悬浮物(TSS)的平均去除率分别为97.6%、98.2%、81.3%和98.1%,出水体积质量平均值分别为89.0、27.1、15.7mg·L^-1和64.9mg·L^-1,满足国家二级排放标准。  相似文献   
169.
170.
污水回用是解决城市缺水问题的一条有效途径。该文提出了一种新方法,尝试利用多孔介质毛细管作用过滤生活污水。制造了4个毛管逆滤渗污水净化器,采用普通河砂作为过滤介质进行了室内试验。试验采用两个因素:水势差、滤池内外径比。水势差选取4个水平:0.11、0.26、0.41、0.56 m,外层与内层水池直径比选取3个水平:14/6、12/6、10/6,以研究利用毛细管作用净化污水的可行性,并定量确定水势差及内外层水池的相对大小对该系统运行效果的影响。用反应器去除污水COD的多少来评价过滤效果。结果表明,过滤速度及净化效果与水势差之间呈极显著的对数相关关系,两者都随着水势差的增大而提高。当水势差为0.56 m时,COD的去除率可高达80%左右,过滤速度可以高达0.15 m/h。外层与内层水池的直径比(D/d)越大滤速越小,但该比值对COD的去除率无明显影响。该装置在运行过程中,污水被过滤介质所覆盖,有效地避免了污水的刺激性气味和蚊蝇孳生对周边环境的影响。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号