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   750篇
  免费   8篇
  国内免费   4篇
安全科学   46篇
废物处理   34篇
环保管理   51篇
综合类   285篇
基础理论   141篇
污染及防治   158篇
评价与监测   29篇
社会与环境   18篇
  2021年   6篇
  2020年   8篇
  2019年   11篇
  2018年   20篇
  2017年   10篇
  2016年   15篇
  2015年   18篇
  2014年   19篇
  2013年   46篇
  2012年   25篇
  2011年   40篇
  2010年   24篇
  2009年   25篇
  2008年   30篇
  2007年   27篇
  2006年   34篇
  2005年   30篇
  2004年   17篇
  2003年   27篇
  2002年   13篇
  2001年   5篇
  2000年   5篇
  1999年   8篇
  1997年   6篇
  1995年   5篇
  1994年   8篇
  1993年   7篇
  1990年   6篇
  1986年   8篇
  1985年   6篇
  1963年   6篇
  1961年   5篇
  1960年   5篇
  1959年   6篇
  1958年   8篇
  1957年   8篇
  1956年   8篇
  1955年   7篇
  1954年   8篇
  1943年   6篇
  1940年   8篇
  1939年   10篇
  1936年   5篇
  1933年   5篇
  1931年   11篇
  1930年   9篇
  1925年   6篇
  1923年   8篇
  1921年   8篇
  1920年   5篇
排序方式: 共有762条查询结果,搜索用时 15 毫秒
61.
A 70,XXX, +18 karyotype was found by chorionic villus sampling, while the fetal fibroblast culture of the affected fetus revealed a 47,XX,+ 18 karyotype. From several possible mechanisms, we assume that a second gamete fusion occurred after the first cell division of the zygote. According to this interpretation, the mosaicism arose in very early pregnancy (at the two-cell stage). This discrepancy can therefore be explained by selection pressure, due to the differentiation processes in the embryonic tissues.  相似文献   
62.
Field application of animal manure is a major cause of odor nuisance in the local environment. Therefore, there is a need for methods for measuring the effect of technologies for reducing odor after manure application. In this work, chemical methods were used to identify key odorants from field application of pig manure based on experiments with surface application by trailing hoses and soil injection. Results from three consecutive years of field trials with full-scale equipment are reported. Methods applied were: membrane inlet mass spectrometry (MIMS), proton-transfer-reaction mass spectrometry (PTR-MS), gold-film hydrogen sulfide (H?S) detection, all performed on site, and thermal desorption gas chromatography with mass spectrometry (TD-GC/MS) based on laboratory analyses of field samples. Samples were collected from a static flux chamber often used for obtaining samples for dynamic olfactometry. While all methods were capable of detecting relevant odorants, PTR-MS gave the most comprehensive results. Based on odor threshold values, 4-methylphenol, H?S, and methanethiol are suggested as key odorants. Significant odorant reductions by soil injection were consistently observed in all trials. The flux chamber technique was demonstrated to be associated with critical errors due to compound instabilities in the chamber. This was most apparent for H?S, on a time scale of a few minutes, and on a longer time scale for methanethiol.  相似文献   
63.
ESP (Electronic Stability Program) has recently been introduced onto the market in an effort to reduce the number and severity of loss-of-control automobile accidents. This reduction is expected to be particularly evident for accidents on roads with low friction (e.g., wet or icy conditions). This study aimed to evaluate the statistical effectiveness of ESP using data from accidents that occurred in Sweden during 2000 to 2002. To control for exposure, induced exposure methods were used, where ESP-sensitive to ESP-insensitive accidents and road conditions were matched in relation to cars equipped with and without ESP. Cars of similar, or in some cases identical, make and model were used to isolate the role of ESP. As predicted, the study showed a positive effect of ESP in circumstances where road surfaces have low friction. The overall effectiveness was 22.1 (+/-21) percent, while for accidents on wet roads, the effectiveness increased to 31.5 (+/-23.4) percent. On roads covered with ice and snow, the corresponding effectiveness was 38.2 (+/-26.1) percent. In addition, ESP was found to be effective for three different types of cars: small front-wheel drive; large front-wheel drive; and large rear-wheel drive.  相似文献   
64.
土地由中心到边缘呈现不同分布利用方式的村庄,构成了欧洲文化景观的基本单元.然而在许多的乡村景观中,那些拥有细致结构的耕地和有树木的草场的真正前工业时代的村庄正在不断失去其原有的结构,这种遗失威胁着文化的继承和生物多样性.因此,监测景观中这样的村庄真实形态的变化范围和速度是非常重要的.随着废弃时间的增加,村庄的真实形态不断丢失,我们所要研究的是怎样的丢失程度才能够通过卫星图像定量分析和目视解译进行评价.1999年,我们在波兰东南部的Bieszczady山脉开展本研究.使用1998年的陆地卫星TM数据,利用景观元素的粒度(田地大小)和土地覆盖组成(灌木和森林的扩侵)对代表真实村庄结构形态退化不同阶段的6种类型村庄进行定量描述.我们利用历史地图勾勒出村庄的边界,并测量从前森林和空地的范围.利用卫星数据,将当前的土地利用和表示成粒度及森林的扩侵状况的土地废弃程度绘制成图.退化沿着2条变化路径发生:被废弃并且最终变成森林,或者形成集约农业.为了验证这样的结果,我们通过对原始卫星影像的目视解译,将1000km2范围内的22个其他村庄分成了4类.而后,我们收集了过去60年人口变化的历史数据.村庄真实形态的分类与人口下降速度明显相关.我们希望验证和应用这种快速评估文化景观真实形态的方法能够得到重视,尤其是在随着欧盟的扩大正在经历或者将要发生巨大变化的欧洲区域.最后,我们论证了村庄具有成为一个融合自然与社会科学的景观尺度的可能性.  相似文献   
65.
Incineration of municipal solid waste is a debated waste management technology. In some countries it is the main waste management option whereas in other countries it has been disregarded. The main discussion point on waste incineration is the release of air emissions from the combustion of the waste, but also the energy recovery efficiency has a large importance.The historical development of air pollution control in waste incineration was studied through life-cycle-assessment modelling of eight different air pollution control technologies. The results showed a drastic reduction in the release of air emissions and consequently a significant reduction in the potential environmental impacts of waste incineration. Improvements of a factor 0.85–174 were obtained in the different impact potentials as technology developed from no emission control at all, to the best available emission control technologies of today (2010).The importance of efficient energy recovery was studied through seven different combinations of heat and electricity recovery, which were modelled to substitute energy produced from either coal or natural gas. The best air pollution control technology was used at the incinerator. It was found that when substituting coal based energy production total net savings were obtained in both the standard and toxic impact categories. However, if the substituted energy production was based on natural gas, only the most efficient recovery options yielded net savings with respect to the standard impacts. With regards to the toxic impact categories, emissions from the waste incineration process were always larger than those from the avoided energy production based on natural gas. The results shows that the potential environmental impacts from air emissions have decreased drastically during the last 35 years and that these impacts can be partly or fully offset by recovering energy which otherwise should have been produced from fossil fuels like coal or natural gas.  相似文献   
66.
We investigated the global metabolite response to artificial selection for tolerance to stressful conditions such as cold, heat, starvation, and desiccation, and for longevity in Drosophila melanogaster. Our findings were compared to data from other levels of biological organization, including gene expression, physiological traits, and organismal stress tolerance phenotype. Overall, we found that selection for environmental stress tolerance changes the metabolomic 1H NMR fingerprint largely in a similar manner independent of the trait selected for, indicating that experimental evolution led to a general stress selection response at the metabolomic level. Integrative analyses across data sets showed little similarity when general correlations between selection effects at the level of the metabolome and gene expression were compared. This is likely due to the fact that the changes caused by these selection regimes were rather mild and/or that the dominating determinants for gene expression and metabolite levels were different. However, expression of a number of genes was correlated with the metabolite data. Many of the identified genes were general stress response genes that are down-regulated in response to selection for some of the stresses in this study. Overall, the results illustrate that selection markedly alters the metabolite profile and that the coupling between different levels of biological organization indeed is present though not very strong for stress selection at this level. The results highlight the extreme complexity of environmental stress adaptation and the difficulty of extrapolating and interpreting responses across levels of biological organization.  相似文献   
67.
This paper is a response to a comment made by Lenzen [1] regarding a paper by Strømman et al. [2]. In this article I comment upon the proposals made by Lenzen. Through this, insights into challenges associated with path based methods in LCA are provided. In particular the application of these to correct for double counting in tiered hybrid LCA. A brief revisit of the rationale for the original work is provided. Key aspects of the methodology are discussed with outset in the comments in [1]. Finally, an assessment of the various approaches, including an option for further improvement is provided.  相似文献   
68.
Homeobox genes regulate development of digits, and it has been suggested that the ratio of length of second to length of fourth digit reflects such genetic effects in a sex-specific manner. We show that digit ratios in the sexually dichromatic house sparrow Passer domesticus differ between sexes, with males having higher ratios than females, and that individuals produce consistent ratios on the two feet. If Homeobox or other genes had pleiotropic effects on development of digits, behavior, and physiology of males and females, we would expect secondary sexual characters and immunity to be related to digit ratio in a sex-specific manner. The size of the visible part of the black badge in February (a secondary sexual character), but not total badge size, was positively correlated with digit ratios, suggesting that males with more male-like digit ratios had larger visible badges. Because of sex-specific effects of development on secondary sexual characters and immunity, we predicted sex-specific differences in immune response to be related to digit ratio. House sparrows with large digit ratios had weaker T cell-mediated immune response than individuals with small digit ratios, particularly in females, implying that females with more male-like digit ratios had weak immune responses. These findings are consistent with the hypothesis that early development, as reflected by digit ratios, and genetics affect the expression of adult characters that are supposedly strongly contributing to fitness.  相似文献   
69.
70.
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