全文获取类型
收费全文 | 1404篇 |
免费 | 123篇 |
国内免费 | 667篇 |
专业分类
安全科学 | 120篇 |
废物处理 | 117篇 |
环保管理 | 275篇 |
综合类 | 982篇 |
基础理论 | 204篇 |
环境理论 | 1篇 |
污染及防治 | 343篇 |
评价与监测 | 29篇 |
社会与环境 | 111篇 |
灾害及防治 | 12篇 |
出版年
2024年 | 6篇 |
2023年 | 26篇 |
2022年 | 71篇 |
2021年 | 59篇 |
2020年 | 64篇 |
2019年 | 75篇 |
2018年 | 72篇 |
2017年 | 93篇 |
2016年 | 96篇 |
2015年 | 106篇 |
2014年 | 134篇 |
2013年 | 145篇 |
2012年 | 148篇 |
2011年 | 131篇 |
2010年 | 109篇 |
2009年 | 112篇 |
2008年 | 70篇 |
2007年 | 118篇 |
2006年 | 101篇 |
2005年 | 70篇 |
2004年 | 61篇 |
2003年 | 65篇 |
2002年 | 53篇 |
2001年 | 37篇 |
2000年 | 32篇 |
1999年 | 29篇 |
1998年 | 16篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有2194条查询结果,搜索用时 31 毫秒
941.
本文指出,把旅游资源优势转化为经济优势是河南旅游业发展的关键,转化的方式是将旅游资源变为旅游产品,转化的原则是市场的需求,转化的步骤是根据市场需求,对旅游资源进行筛选,加工成适销对路的产品再推向旅游市场. 相似文献
942.
Markus Metz Georg M. Klump Thomas W. P. Friedl 《Behavioral ecology and sociobiology》2007,61(9):1369-1381
The red bishop (Euplectes orix) is a highly polygynous and colonial weaverbird. Males construct several nests within their territories to which they try
to attract females, and females are solely responsible for incubation and raising offspring. In this paper, we describe the
characteristics of the red bishop’s mating system as a biological market and investigate the role of nests built by males
as a traded commodity in a mating market. As timing of breeding in red bishops in arid and semi-arid zones depends on rainfall
patterns which are often unpredictable, there are temporal changes in demand for and supply of nests within a breeding season,
with breeding activities of males and females being highly synchronised. We found that males increased their nest-building
speed with increased female breeding activity independently of rainfall, indicating that supply follows demand in this mating
market. The supply of nests was always larger than the demand for nests. Construction costs for nests increased with demand
for nests as indicated by shorter nest-building duration and shorter building delays between two consecutively built nests
at times of high breeding activity. Males as a trading class are chosen according to the age of their nests offered, with
young nests having a higher probability of being accepted by females. Furthermore, female choosiness with regard to nest age
decreased when their own market value decreased, as predicted by biological market theory. The temporal changes of breeding
activity together with the female preference for young and fresh nests require that males quickly adjust nest-building activity
to varying female demand for new nests. However, males with a better adjustment of building speed to female breeding activity
did not gain higher mating success. 相似文献
943.
Influence of iron, nickel and cobalt on biogas production during the anaerobic fermentation of fresh residual biomass 总被引:2,自引:0,他引:2
We have investigated the dependence of the rate of the production of biogas upon the concentration of nickel, cobalt and iron at sub-toxic concentration and monitored its composition as amount of hydrogen, methane and carbon dioxide. The distribution of the added metals between the liquid and solid phase has also been monitored.
The results of our investigations show that the addition of any of the listed metals to the sludge may cause the production of a higher amount of biogas and influence the methane or carbon dioxide percentage. Conversely, the effect on the hydrogen production depends upon the metal added, the age of the active sludge used, and its adaptation to the susbtrate. As a general feature, during the acidogenesis phase, nickel reduces, while iron increases, the percentage of dihydrogen in the biogas, while cobalt has no influence. 相似文献
The results of our investigations show that the addition of any of the listed metals to the sludge may cause the production of a higher amount of biogas and influence the methane or carbon dioxide percentage. Conversely, the effect on the hydrogen production depends upon the metal added, the age of the active sludge used, and its adaptation to the susbtrate. As a general feature, during the acidogenesis phase, nickel reduces, while iron increases, the percentage of dihydrogen in the biogas, while cobalt has no influence. 相似文献
944.
945.
946.
细菌Rieske型非血红素铁加氧酶研究进展 总被引:2,自引:2,他引:2
细菌Rieske型非血红素铁加氧酶是催化芳香化合物好氧降解第一步反应的酶,能够激发好氧环境下大量芳香或取代芳香化合物的生物降解,同时还可作为有机化合物的合成子.这是一类新型且丰富的酶资源,在受污环境的生物修复方面有着巨大的潜力,并且符合“绿色化学”的要求.本文综述了该类酶的分类、晶体结构、作用机理及其基因改造等最新研究进展. 图4表1参17 相似文献
947.
Hu Y Li JH Zhu YG Huang YZ Hu HQ Christie P 《Environmental geochemistry and health》2005,27(2):169-176
A pot experiment was carried out in a greenhouse to investigate the sequestration of As in iron plaques on root surface of
three rice (Oryza sativa L.) cultivars. Phosphate (P) fertilization increased both plant biomass and tissue P concentrations significantly, indicating
that the soils used in this study was highly P-deficient. Results from this study confirmed that low P supply improved the
formation of iron plaque on rice roots. As a consequence, arsenic (As) concentrations in DCB-extracts with no P addition were
significantly higher than those with P fertilization. Arsenic was highly sequestrated in iron plaque; arsenic concentration
in iron was up to nearly 120 mg kg−1, while arsenic concentrations in roots were just several mg kg−1. Both arsenic and phosphate concentrations in iron plaque were highly positively correlated with the amounts of iron plaque
(DCB-extractable Fe). Contrary to normal understanding that increasing P supply could reduced As accumulation in plants, results
from the present study showed that P fertilization did not inhibit the As uptake by plants (As accumulation in aboveground),
which was probably due to the fact that iron plaque formation was improved under low P conditions, thus leading to more As
sequestration in the iron plaque. Thus results obtained in this study indicated that the iron plaque may inhibit the transfer
of As from roots to shoots, and thus alter the P–As interaction in plant As uptake processes. 相似文献
948.
949.
原子吸收法测定水中铁的不确定度分析 总被引:6,自引:0,他引:6
通过对原子吸收法测定水中铁的不确定度的分析,找出了导致不确定度的因素。对测量不确定度进行计算和评定,结果表明,影响其测量不确定度的主要因素是标准曲线精密度以及仪器漂移。 相似文献
950.
用铁泥制备高效无机絮凝剂聚硅酸铁及其絮凝性能研究 总被引:6,自引:0,他引:6
马淞江 《环境污染治理技术与设备》2006,7(9):130-133
研究了以铁泥、硅酸钠为原料,制备高效絮凝剂聚硅酸铁(PSF)的方法,确定了合理的生产工艺和操作条件。并对絮凝剂PSF处理工业废水的絮凝性能进行了研究,探讨了PSF处理工业废水的反应机理。结果表明,PSF具有良好的絮凝性能,是一种比聚合硫酸铁(PFS)性能更优良的絮凝剂。 相似文献