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   265篇
  免费   10篇
  国内免费   13篇
林业   22篇
农学   4篇
基础科学   9篇
  93篇
综合类   138篇
农作物   2篇
水产渔业   2篇
畜牧兽医   14篇
园艺   1篇
植物保护   3篇
  2024年   1篇
  2023年   2篇
  2022年   3篇
  2021年   5篇
  2020年   5篇
  2019年   8篇
  2018年   4篇
  2017年   10篇
  2016年   11篇
  2015年   11篇
  2014年   21篇
  2013年   27篇
  2012年   24篇
  2011年   17篇
  2010年   20篇
  2009年   24篇
  2008年   16篇
  2007年   14篇
  2006年   7篇
  2005年   7篇
  2004年   7篇
  2003年   6篇
  2002年   3篇
  2001年   2篇
  2000年   4篇
  1999年   6篇
  1998年   3篇
  1997年   3篇
  1996年   4篇
  1995年   4篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1990年   3篇
  1988年   1篇
  1987年   1篇
排序方式: 共有288条查询结果,搜索用时 15 毫秒
81.
介绍了纤维板车间的煤耗、水耗情况 ,讨论了节煤和节水途径。重点论述了锅炉机械不完全燃烧热损失 q4 与锅炉排烟热损失 q2 偏大的原因及降低的途径。  相似文献   
82.
[目的]为了探明改良剂与土壤Cu和Cd的作用规律。[方法]通过解吸试验和土培试验,分析粉煤灰和石灰为化学改良剂对矿区土壤Cu和Cd化学形态的影响。[结果]当粉煤灰和石灰用量分别为土重的5.00%和0.10%时,Cu和Cd的浸提量可控制在阈值内(TCLP,USEPA)。[结论]粉煤灰和石灰可有效降低土壤重金属可提取态的含量。  相似文献   
83.
针对高潜水位采煤塌陷区受损特点和农业经济发展态势,以江苏省徐州市贾汪区土地整理项目区为对象,开展3方面研究:①在框架导向的基础上,提出结合人与自然和谐观与问题导向的土地整理规划设计理念和技术路线;②提出土地平整、田间道路、农田水利、田间道路、农田防护林、生态坑塘等特色工程布局;③针对采煤塌陷区区特有潜水位上升,生态环境恶化与土壤质量及结构受到破坏等现状,提出生态型降水排水沟道与土壤修复工程等特色设计。这一针对性的土地整理规划设计为高潜水位采煤塌陷区科学开展土地整理,科学恢复生产能力,重建农田生态和区域土地利用效率的提高提供了科学借鉴。  相似文献   
84.
Abstract

Fly ash from the coal‐burning industry may be a potential inorganic soil amendment to increase rice productivity and to restore the soil nutrient balance in paddy soil. In this study, fly ash was applied at rates of 0, 40, 80, and 120 Mg ha?1 in two paddy soils (silt loam in Yehari and loamy sand in Daegok). During rice cultivation, available phosphorus (P) increased significantly with fly ash application, as there was high content of P (786 mg kg?1) in the applied fly ash. In addition, high content of silicon (Si) and high pH of fly ash contributed to increased available‐P content by ion competition between phosphate and silicate and by neutralization of soil acidity, respectively. With fly‐ash application, water‐soluble P (W‐P) content increased significantly together with increasing aluminum‐bound P (Al‐P) and calcium‐bound P (Ca‐P) fractions. By contrast, iron‐bound P (Fe‐P) decreased significantly because of reduction of iron under the flooded paddy soil during rice cultivation. The present experiment indicated that addition of fly ash had a positive benefit on increasing the P availability.  相似文献   
85.
This study was conducted to assess changes in soil properties of a soil that received a one-time application (360 Mg ha?1) of fluidized bed combustion material (FBCM) 23 years earlier. Soil samples were taken at three depths (0–10, 10–20, and 20–30 cm). Samples were also collected from an adjacent field with the same soil type for control. Hot nitric acid and Mehlich 3 extractions were used for total and extractable elements. Analyses indicated improvement in soil physical and chemical properties after 23 years of FBCM application. For example at the 20- to 30-cm depth, soil pH values increased from 4.9 to 7.7, whereas calcium concentrations increased from 0.23 to 1.52 g kg?1 with FBCM amendment. In most cases, metal concentrations were less with FBCM amendment. Results from this study demonstrated that soil physical and chemical improvements from FBCM were maintained even 23 years after an extremely high application of FBCM.  相似文献   
86.
抚顺西露天矿大型煤矸石山及其周边土壤重金属污染研究   总被引:5,自引:1,他引:4  
对抚顺西露天矿煤矸石山表层及其周边0~1500m范围土壤进行多点分层取样,分析测定土壤样品中Cd、Cr、Cu、Pb、Ni等重金属元素含量。结果表明:矸石山碳质页岩与绿色泥岩重金属Cd含量较高,表层风化物中Cd、Ni含量较高,超过土壤环境质量2级标准,其中一些样点超过3级标准。随着与矸石山距离的增加,周边西南部风向方向上土壤Cd、Cr、Ni、Cu含量呈现规律性递减趋势。重金属Cd、Cr、Ni在20~40cm含量大于0~20cm含量,表明其具有一定的纵向迁移性。矸石山表层与周边邻近土壤pH较高,可有效减低重金属污染风险。  相似文献   
87.
济宁引黄复垦区不同年限土壤养分变化预测   总被引:1,自引:0,他引:1  
在济宁市梁山县选择引黄充填复垦典型复垦地块,并选择一块具有相同耕作方式的未塌陷地作为参照,通过分析复垦样地多年来的观测数据,构建不同土壤养分指标与年限间的回归方程,研究同一复垦方式不同复垦年限的土壤养分变化,并对耕层土壤养分恢复时间进行预测。结果表明:(1)随着复垦年限的增加,土壤有机质、碱解氮、有效磷、速效钾含量均呈增加的趋势,至复垦5a时,土壤有机质、碱解氮、速效钾基本趋近于对照地块含量,有效磷含量虽总体呈上升趋势,但复垦5 a后0~20 cm、20~40 cm、40~60 cm土壤有效磷含量分别为6.34、6.21、5.93 mg·kg~(-1),仅达到对照地块的60%;(2)预测引黄充填复垦耕层土壤有机质、碱解氮和速效钾含量在5~6 a后可恢复至对照耕地水平,复垦地块耕层土壤有效磷含量如要恢复至对照耕地水平需要15 a。引黄充填复垦地块耕层土壤的供磷能力明显较弱,可通过改善农艺措施和后期合理增施磷肥或有机肥料来提升土壤质量。  相似文献   
88.
王锐  李希来  马钰  仁欠端智  王彩云  赵洁  张静 《土壤》2020,52(2):386-393
针对高寒地区露天煤矿开采产生的煤矸石堆积对多年冻土区高寒湿地的影响问题,本文通过地面调查、取样比较,研究分析了矿区周边高寒湿地植被和土壤特征对煤矸石渣山堆积的响应。结果表明,矿区煤矸石堆积的4年时间已经对周边近、中、远不同距离(300m,650m,1000m)高寒湿地植被和土壤产生了一定程度的影响,引起原生莎草类盖度和高度减小,靠近煤矸石渣山区域的牧草高度降低,中距离杂草平均高度比近距离高2.65cm。矸石堆积造成周围土壤容重增加,全氮和有机质含量逐渐减少,远距离0-10 cm土层全氮和有机质平均含量分别是近距离的1.16和1.20倍。高寒湿地土壤真菌和放线菌数量减少, 0-10cm土层近距离样区真菌数量仅为中距离的51.8 %,中距离样区放线菌数量分别是近距离和远距离的4.32和3.4倍。除锌元素和镉元素以外,煤矸石堆积没有显著影响土壤砷、铬、镍、铜、汞、铅等6种重金属元素含量。随机森林算法分析表明,杂草类高度,Zn元素含量,土壤容重、莎草盖度、有机质含量是煤矸石堆积对周围高寒湿地影响的主要因子。  相似文献   
89.
In the Lusatian mining district, rehabilitated mine soils contain substantial amounts of lignite in addition to recent carbon derived from plant litter. The aim of this study was to examine the importance of the two organic matter types as substrates for soil microbial biomass in mine soils containing organic matter with a contrasting degree of humification. Samples were taken from the lignite-containing overburden material, from a mine soil under 14-year-old black pine (Pinus nigra) and from a mine soil under 37-year-old red oak (Quercus rubra). Overburden material was ameliorated with alkaline ash and incubated in an identical manner as the 14-year-old and 37-year-old mine soils for 16 months. Carbon mineralisation was monitored throughout. After 0, 3, 6, 12 and 16 months, samples were removed and analysed for chemical parameters and for microbial biomass. In addition, 14C activity measurements in bulk soil and microbial biomass were used to estimate their lignite content.Despite the high content of organic carbon in lignite-rich overburden material, low contents of microbial biomass were recorded. Ash-amelioration led to high pH values in the overburden material, resulting in high concentrations of dissolved organic carbon most likely derived from lignite. Development of the microbial community was subsequently stimulated by presence of an easily available carbon source. In older mine soils, larger amounts of microbial biomass are most likely related to the presence of recent organic matter. Radiocarbon analysis of the microbial biomass extracted from the 14-year-old mine soil indicated higher lignite carbon contribution than recorded for microbial biomass of the 37-year-old mine soil. The highest concentration of lignite C present in microbial biomass as indicated by the Cmic/Corg ratio was, however, observed in the ameliorated overburden material. Therefore, we conclude that the importance of lignite as a carbon source for micro-organisms decreases when recent organic matter is present in the older stages of mine soil development.  相似文献   
90.
矿区生态重建过程中的土地利用/覆被变化   总被引:4,自引:1,他引:4  
以平朔矿区为例,采用野外定点调查、室内分析、历史资料查证等相结合的方法,研究了黄土区大型露天矿生态重建中的土地利用/覆被变化。结果表明:矿区土地作为一种特殊的土地利用形式,土地利用/覆被变化异常剧烈,其中,地貌重塑过程中的土地利用/覆被变化主要体现在海拔高度、坡向、坡度、坡型、比表面积的变化;土壤重构过程中的土地利用/覆被变化主要体现在土壤物理性状、化学性状、生物性状及侵蚀性状发生变化;植被重建过程中的土地利用/覆被变化主要体现在91种人工植被的增加和95种野生植被的侵入。  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