全文获取类型
收费全文 | 2446篇 |
免费 | 300篇 |
国内免费 | 651篇 |
专业分类
安全科学 | 428篇 |
废物处理 | 54篇 |
环保管理 | 238篇 |
综合类 | 1516篇 |
基础理论 | 348篇 |
污染及防治 | 296篇 |
评价与监测 | 255篇 |
社会与环境 | 129篇 |
灾害及防治 | 133篇 |
出版年
2024年 | 24篇 |
2023年 | 53篇 |
2022年 | 110篇 |
2021年 | 112篇 |
2020年 | 129篇 |
2019年 | 123篇 |
2018年 | 117篇 |
2017年 | 151篇 |
2016年 | 154篇 |
2015年 | 152篇 |
2014年 | 148篇 |
2013年 | 213篇 |
2012年 | 195篇 |
2011年 | 189篇 |
2010年 | 135篇 |
2009年 | 173篇 |
2008年 | 120篇 |
2007年 | 149篇 |
2006年 | 140篇 |
2005年 | 127篇 |
2004年 | 89篇 |
2003年 | 104篇 |
2002年 | 62篇 |
2001年 | 62篇 |
2000年 | 54篇 |
1999年 | 51篇 |
1998年 | 44篇 |
1997年 | 50篇 |
1996年 | 42篇 |
1995年 | 24篇 |
1994年 | 16篇 |
1993年 | 14篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 3篇 |
排序方式: 共有3397条查询结果,搜索用时 656 毫秒
341.
阐述了生物膜系统中与降解基因有关的水平基因转移的研究进展,表明生物膜中致密的群落结构增加了细菌间水平基因转移的效率.近年发展起来的研究策略和新的分子生物学方法使人们能对自然和人工模拟状态下的水平基因转移进行更精细的分析,降解基因在环境中的水平传播促进了难降解有机物的生物降解,尤其是携带降解基因的接合质粒向原位细菌种群中的转移在生物强化中具有巨大的潜力.参23 相似文献
342.
燃煤灰渣中微量元素分布规律的研究 总被引:23,自引:2,他引:23
研究了锅炉飞灰和底灰中15种微量元素的含量和分布,探讨了煤炭燃烧后,微量元素在灰渣中的集散及其影响因素,飞灰和底灰中大多数元素高于全国土壤背景值,7种元素高于克拉克值,其余8种低于克拉克值,飞灰中多数元素的地球化学富集因子高于1,呈富集状态,而底灰中多数元素富集因子小于1,飞灰和底灰中微量元素含量与煤中微量元素含量呈线性关系,微量元素含量不仅与煤有关,还受锅炉燃烧方式等人为因素影响。 相似文献
343.
344.
Summary 2-methyl-1,4-benzoquinone as a target compound of the tergal gland secretion of the rove beetle,Aleochara curtula, was quantified from the reservoirs of individual beetles. Males store less secretion than females, and they evaporate more of the secretion as measured by adsorption from the air (closed-loop-stripping-analysis). The amount of emitted quinone is increased during aggressive interactions of rival males. The pulsed emission of the secretion during aggression is demonstrated by a novel technique combining observation of behavior with the on-line measurement of target fragment ions by mass-spectrometry (tandem bioassay — mass fragmentography). The emission of the secretion is used as a weapon in combats between males and may result in the repulsion of subordinate males from the mating site, but may also serve to mimic females chemically in order to avoid aggressive encounters. 相似文献
345.
水平基因转移加速了部分生物体基因组的进化和革新;但随着基因改造生物的大量运用,由水平基因转移引起的生态安全问题越来越成为人们争论的焦点.由于大量异生污染物的产生,污染地区成为细菌水平基因转移的一个"热点"区域.为了实现污染地区的生物修复及强化难降解废水处理的效果,人为的制造和加快特定降解基因的水平转移被认为是解决这些问题的一个新思路.图2参57 相似文献
346.
Social network theory has made major contributions to our understanding of human social organisation but has found relatively
little application in the field of animal behaviour. In this review, we identify several broad research areas where the networks
approach could greatly enhance our understanding of social patterns and processes in animals. The network theory provides
a quantitative framework that can be used to characterise social structure both at the level of the individual and the population.
These novel quantitative variables may provide a new tool in addressing key questions in behavioural ecology particularly
in relation to the evolution of social organisation and the impact of social structure on evolutionary processes. For example,
network measures could be used to compare social networks of different species or populations making full use of the comparative
approach. However, the networks approach can in principle go beyond identifying structural patterns and also can help with
the understanding of processes within animal populations such as disease transmission and information transfer. Finally, understanding
the pattern of interactions in the network (i.e. who is connected to whom) can also shed some light on the evolution of behavioural
strategies. 相似文献
347.
Shinnosuke Nakayama Reiji Masuda Masaru Tanaka 《Behavioral ecology and sociobiology》2007,61(9):1383-1390
Grouping behavior has various types of antipredator functions. Some of these functions require social transmission of information,
such as the many-eyes effect, whereas others do not, such as the dilution and confusion effects. Functions of grouping behavior
would enhance with social transmission among group members. We investigated and compared the onsets of schooling behavior
and social transmission of information in chub mackerel Scomber japonicus. Onset of schooling behavior was observed in rearing tanks by calculating the degree of parallel swimming. Onset of social
transmission was examined by using visual cues from conspecifics. A group of five individuals was put in each of three experimental
chambers from which they could see a group of conspecifics in the neighboring chamber. A weak electric stimulus was given
to one of these chambers, and information transfer among individuals was observed. We found that social transmission by visual
cues started on 30 days posthatching (25.1 mm in standard length), which was 2 weeks after the onset of schooling behavior.
The late onset of social transmission relative to schooling behavior might be attributed to different predation pressure with
development, or by underdevelopment of optic tectum, as the volume of the optic tectum did not increase just after the onset
of schooling behavior. 相似文献
348.
广州城郊环境梯度下马尾松针叶元素质量分数变化特征 总被引:1,自引:0,他引:1
城市化、工业化迅速发展及人类活动的加剧给城市及其周边地区森林生态系统带来前所未有的干扰和压力。植物冠层是植物与大气直接进行气体交换的界面,冠层叶组织化学分析已成为评价环境污染对森林树木健康的影响,指示环境污染的有效手段。文章以广州黄埔工业区(丹水坑风景区)、城郊接壤区(华南植物园)和近郊(帽峰山森林公园)这一环境梯度为对象,在各研究点上选定自然生长的、成熟健康的马尾松(Pinus massonianaL.)5株,分别采集树冠中部向阳枝条上的当年生(Current,C)和一年生(Current 1,C 1)针叶,然后将每组针叶区分为带叶鞘针叶、去叶鞘针叶和叶鞘3个组分进行样本制备,测定N、Al、Cu、Cd、Pb、Zn、Cr、Ni元素质量分数,旨在探讨利用马尾松针叶不同组分的元素质量分数用于指示城郊梯度环境质量变化的适宜性和可靠性。研究结果表明:①当年生带叶鞘针叶中Al质量分数显著高于当年生去叶鞘针叶(p<0.05),其余元素在当年生和一年生的去叶鞘针叶与带叶鞘的完整针叶间均无显著差异;②Ni在当年生针叶及其叶鞘间没有显著差异(p<0.05),其它被测定的金属元素无论在当年生还是一年生针叶中,均表现为叶鞘中的元素质量分数均显著高于去叶鞘针叶(p<0.05),体现了针叶与叶鞘在形态结构上的差异引起重金属积累的差异;而非金属元素N质量分数则针叶显著高于叶鞘;③一年生针叶中Ni质量分数显著低于当年生针叶,但Al、Pb、Zn质量分数显著高于当年生针叶,一年生叶鞘中所有金属元素的质量分数都显著高于当年生叶鞘,表现出随暴露时间和针叶寿命的延长而持续累积的特征;而营养元素N质量分数在当年生针叶和一年生针叶以及当年生叶鞘和一年生叶鞘间无显著差异;④城乡环境梯度下生长的马尾松为研究环境质量演变提供了一个天然的实验室,受人类活动干扰大的城区马尾松一年生针叶的Cd和N质量分数及其叶鞘中的Cu、Cr、Ni质量分数显著高于受人为干扰较少的郊区,表明植物组织中元素化学特征反映了城市发展过程中人类活动的足迹。在城市环境尤其是重金属污染的监测中,成熟的一年生叶鞘更具指示意义,效果更显著。 相似文献
349.
Abstract: Forest-associated species in fragmented landscapes must traverse potentially inhospitable gaps to move between habitat patches. Although conservation biologists advocate connecting patches with corridors or improving the matrix to make it suitable for movement, little is known about the factors influencing gap-crossing decisions for most species. We investigated gap crossing by the red squirrel ( Tamiasciurus hudsonicus ) in logged landscapes in southeastern Alaska, where the species avoids microhabitats associated with gaps created by clearcutting. We released individuals across clearcuts and determined the routes they took home with tracking spools and radio telemetry. Of 36 adult red squirrels translocated across six clearcuts, 14 crossed clearcuts to reach home. Squirrels were more likely to cross clearcuts if the detour efficiency (distance to home crossing gap divided by distance of forested detour) was low, indicating an ability to compare distances along alternate routes and travel costs or risks in different habitats. No other landscape metrics, such as gap size or crossing distance, predicted crossing behavior. Red squirrels of low body mass were more likely to cross clearcuts, where the probability of encountering conspecifics is low. Distance predicted route choice for squirrels detouring around clearcuts. Indirect evidence suggests that perceived predation risk, energetic costs, or both are higher in clearcuts. Detour efficiency reportedly influences the gap-crossing decisions of some forest-associated birds, but this is the first demonstration of its role in gap-crossing decisions by a mammal. 相似文献
350.
三种类型油菜(Brassica spp.)和野芥菜(B. juncea var.gracilis Tsen et Lee)杂交亲和性及F1的适合度--潜在基因转移的研究 总被引:11,自引:0,他引:11
通过人工去雄授粉,采用荧光显微镜观察了3种类型栽培油菜花粉在两地采集的野芥菜柱头上的萌发生长情况,结合杂交后的结实率,探讨了3种类型油菜和野芥菜杂交的亲和性.结果表明,甘蓝型油菜和芥菜型油菜与野芥菜的亲和性都非常高,亲和性指数达10.0以上,而白菜型油菜和野芥菜的亲和性较低,亲和指数小于0.2.子一代的适合度研究结果表明,芥菜型油菜向野芥菜杂交一代的适合度没有降低,而甘蓝型及白菜型和野芥菜杂交一代的适合度明显下降,表现在花粉活力降低,结实率极低.上述结果表明,白菜型油菜和野芥菜的基因转移可能性最小,甘蓝型居中,而芥菜型极易向野芥菜发生基因转移. 相似文献