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   731篇
  免费   69篇
  国内免费   161篇
安全科学   102篇
废物处理   10篇
环保管理   110篇
综合类   444篇
基础理论   122篇
污染及防治   60篇
评价与监测   70篇
社会与环境   11篇
灾害及防治   32篇
  2023年   7篇
  2022年   11篇
  2021年   26篇
  2020年   17篇
  2019年   17篇
  2018年   23篇
  2017年   25篇
  2016年   30篇
  2015年   43篇
  2014年   40篇
  2013年   52篇
  2012年   58篇
  2011年   62篇
  2010年   47篇
  2009年   56篇
  2008年   38篇
  2007年   61篇
  2006年   70篇
  2005年   51篇
  2004年   38篇
  2003年   29篇
  2002年   27篇
  2001年   27篇
  2000年   27篇
  1999年   18篇
  1998年   12篇
  1997年   10篇
  1996年   10篇
  1995年   7篇
  1994年   6篇
  1993年   3篇
  1992年   4篇
  1991年   4篇
  1990年   2篇
  1987年   1篇
  1986年   1篇
  1974年   1篇
排序方式: 共有961条查询结果,搜索用时 411 毫秒
791.
猪场生物发酵床垫料卫生研究   总被引:1,自引:0,他引:1  
通过选择有3个采用发酵床养猪模式的猪场,采集不同使用年限、不同深度及饲养不同阶段猪舍的发酵床垫料,通过测定水分、总N、总P、可溶性盐、黄曲霉毒素B1(AFB1)、枯草芽孢杆菌和大肠杆菌数目、Cu和Zn含量(全重金属及有效态重金属)评估垫料的卫生学状况.并将垫料与土壤以不同比例混合,研究对植物生长及Cu、Zn在植株中残留影响.研究表明,发酵床垫料随着深度增加,垫料的水分含量逐渐降低,温度逐渐升高,大肠杆菌、枯草芽孢杆菌数量减少.随着发酵床使用年限的延长,总N随垫料使用时间延长而变低,而总P含量随时间延长而增加,但变化均不显著(P>0.05);Cu、Zn、Pb、可溶性盐含量都呈现显著的增加(P<0.05).在1年、2年、3年期的垫料中AFB1均有检出,含量均小于10 μg/kg.种植实验结果显示,土壤添加垫料后,Cu、Zn含量随着添加比例增加而增加,植物中残留量随着垫料添加比例的增加而增加.因此在处理发酵床垫料时,要综合考虑其对环境及食品安全的影响.  相似文献   
792.
餐饮业废油脂皂化工艺的探索   总被引:2,自引:0,他引:2  
研究了废油脂的皂化方法和皂化机理。通过红外光谱分析废油脂皂化样品 ,对皂化度的影响因素进行了讨论。摸索出最佳皂化工艺条件 :皂化时间 4h ,皂化温度 10 0℃ ,碱液用量 (NaOH与废油脂的质量比 ) 1∶2 ,皂化用NaOH碱液浓度为 30 %。  相似文献   
793.
紫茎泽兰(Eupatorium adenophorum Spreng),菊科多年生草本或半灌木植物,是世界性入侵杂草,也是目前危害我国最为严重的外来入侵杂草之一,对我国西南地区农业、畜牧业的良好发展以及生态环境造成了严重的危害。种子繁殖是紫茎泽兰初始建群,尤其是远距离传播的主要途径。环境对种子萌发具有决定性作用,对于物种的生存具有重要意义。因此,本试验通过室内生测法分析了紫茎泽兰种子保存时间、种内竞争及环境温度、盐分胁迫及水分胁迫等因素对紫茎泽兰种子萌发的影响。结果表明:紫茎泽兰种子寿命较长,存放2.5年的种子萌发率仍可达45.67%;紫茎泽兰种子萌发时种内竞争作用较强,能够显著降低其种子的萌发势和萌发率;紫茎泽兰种子萌发所需的温度范围较宽,在12~30℃温度范围内均可萌发,且随环境温度的升高,种子萌发越快,萌发率越高,高温(30℃/22℃)处理下种子萌发率可达到90.33%;同时发现,紫茎泽兰种子萌发对环境中的盐分浓度十分敏感,0.25%的盐质量分数即可达到种子的致死水平,1%的盐质量分数处理即可使种子完全丧失萌发能力。紫茎泽兰种子较耐水淹环境,浸水处理6 d的种子的萌发率仍高达65.68%。由此表明,紫茎泽兰种子不适应盐碱环境,而适宜于温暖潮湿的自然环境。这为探析紫茎泽兰种子萌发活动生理提供了一定的基础资料,同时,也为有效、安全的防除紫茎泽兰提供了科学依据。  相似文献   
794.
Benthic infauna were sampled from 251 Southern California Bight (SCB) mainland shelf sites in the summer of 1994. Sample sites were selected using a stratified random design, with the primary strata being depth zone, geography, and proximity to point and non-point discharges. Benthic infaunal condition was assessed using the Benthic Response Index (BRI), and by comparing dominant taxa and community parameters (e.g., number of taxa) among strata. Ninety-one percent of sediments in the SCB were found to contain healthy benthic communities. Most stations with altered benthos were located near river mouths, in Santa Monica Bay, or on the Palos Verdes Shelf. Deviations at sites with altered benthic communities were mostly limited to minor changes in species composition, rather than to large declines in diversity or abundance.  相似文献   
795.
气相色谱法测定元素磷时应注意的几个问题   总被引:1,自引:0,他引:1  
阐述了气相色谱法测定水中元素磷时盐析剂、振荡次数(幅度)、振荡时间和干扰物对测定的影响,确定了最佳测定条件及消除干扰的方法。  相似文献   
796.
灰霾天气条件下天津市环境空气中颗粒物污染特征分析   总被引:8,自引:1,他引:7  
针对天津地区灰霾天气条件下环境空气中颗粒物的污染程度及变化特征进行分析。指出出现灰霾天气是污染加重的直观反映,将其发展成为一项环保指标,将对大气污染控制起到一定的积极作用。  相似文献   
797.
798.
Australian reporting requirements for native vegetation require improved spatial and temporal information on the anthropogenic effects on vegetation. This includes better linkage of information on vegetation type (e.g., native vegetation association), extent and change, vegetation condition, or modification. The Vegetation Assets, States and Transitions (VAST) framework is presented as a means for ordering vegetation by degree of anthropogenic modification as a series of condition states, from a residual or base-line condition through to total removal. The VAST framework facilitates mapping and accounting for change and trends in the status and condition of vegetation. The framework makes clear the links between land management and vegetation condition states, provides a mechanism for describing the consequences of land management practices on vegetation condition, and contributes to an understanding of resilience. VAST is a simple communication and reporting tool designed to assist in describing and accounting for anthropogenic modification of vegetation. A benchmark is identified for each vegetation association. Benchmarks are based on structure, composition, and current regenerative capacity. This article describes the application of the VAST framework as a consistent national framework to translate and compile existing mapped information on the modification of native vegetation. We discuss the correspondence between these compiled VAST datasets at national and regional scales and describe their relevance for natural resource policy and planning.  相似文献   
799.
Reproduction in birds requires the input of time and energy during discrete breeding phases leading to investment trade-offs between laying date, clutch size, body mass, and incubation constancy. We investigated costs during incubation by experimentally enlarging 25 clutches of white-tailed ptarmigan Lagopus leucurus. The experiment was conducted in 2 years, one with harsh weather that forced a natural delay in reproduction. When forced to delay egg-laying, females began incubation with poorer body condition and foraged more during incubation. Rates of mass loss during incubation were not affected by clutch enlargement, and did not differ between harsh and benign years; however, females that were heavier at the start of incubation lost more mass than lighter females. Clutch-enlarged females had reduced nest attendance compared to control birds in both years and incubation periods increased by up to 2 days relative to controls. In the harsh year, there was a trend for clutch-enlarged females to have lower nest success, but there was no effect on overwinter survival. Different behavioral responses by females in the 2 years showed that incubation costs may depend on other factors such as female quality, food supply, or weather conditions. Incubation is a dynamic period during which birds may adjust energy balances by varying body condition and food intake. Received: 28 March 2000 / Received in revised form: 18 August 2000 / Accepted: 2 July 2000  相似文献   
800.
张锐波  张丽萍 《灾害学》2000,15(2):66-69
将 1 999年世界灾难性地震进行灾情与成因分析 ,总结出其特点及造成严重灾难的人为因素 ,最后综述了世界性地震预测的一些主要结论  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