全文获取类型
收费全文 | 980篇 |
免费 | 49篇 |
国内免费 | 382篇 |
专业分类
安全科学 | 67篇 |
废物处理 | 56篇 |
环保管理 | 75篇 |
综合类 | 537篇 |
基础理论 | 204篇 |
污染及防治 | 331篇 |
评价与监测 | 38篇 |
社会与环境 | 35篇 |
灾害及防治 | 68篇 |
出版年
2024年 | 1篇 |
2023年 | 27篇 |
2022年 | 56篇 |
2021年 | 43篇 |
2020年 | 38篇 |
2019年 | 28篇 |
2018年 | 36篇 |
2017年 | 55篇 |
2016年 | 48篇 |
2015年 | 68篇 |
2014年 | 73篇 |
2013年 | 99篇 |
2012年 | 83篇 |
2011年 | 108篇 |
2010年 | 90篇 |
2009年 | 60篇 |
2008年 | 85篇 |
2007年 | 61篇 |
2006年 | 54篇 |
2005年 | 52篇 |
2004年 | 32篇 |
2003年 | 27篇 |
2002年 | 26篇 |
2001年 | 20篇 |
2000年 | 20篇 |
1999年 | 27篇 |
1998年 | 21篇 |
1997年 | 12篇 |
1996年 | 15篇 |
1995年 | 22篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有1411条查询结果,搜索用时 31 毫秒
341.
342.
Fossil record of Phanerozoic non-spicular sponges, beside of being important with respect to the lineage evolution per se, could provide valuable references for the investigation of Precambrian ancestral animal fossils. However, although modern phylogenomic studies resolve non-spicular demosponges as the sister group of the remaining spiculate demosponges, the fossil record of the former is extremely sparse or unexplored compared to that of the latter; the Middle Cambrian Vauxiidae Walcott 1920, is the only confirmed fossil taxon of non-spicular demosponges. Here, we describe carbonate materials from Devonian (Upper Givetian to Lower Frasnian) bioherms of northern France and Triassic (Anisian) microbialites of Poland that most likely represent fossil remnants of keratose demosponges. These putative fossils of keratose demosponges are preserved as automicritic clumps. They are morphologically distinguishable from microbial fabrics but similar to other spiculate sponge fossils, except that the skeletal elements consist of fibrous networks instead of assembled spicules. Consistent with the immunological behavior of sponges, these fibrous skeletons often form a rim at the edge of the automicritic aggregate, separating the inner part of the aggregate from foreign objects. To confirm the architecture of these fibrous networks, two fossil specimens and a modern thorectid sponge for comparison were processed for three-dimensional (3-D) reconstruction using serial grinding tomography. The resulting fossil reconstructions are three-dimensionally anastomosing, like modern keratose demosponges, but their irregular and nonhierarchical meshes indicate a likely verongid affinity, although a precise taxonomic conclusion cannot be made based on the skeletal architecture alone. This study is a preliminary effort, but an important start to identify fossil non-spicular demosponges in carbonates and to re-evaluate their fossilization potential. 相似文献
343.
Immigrant bacteria located on leaf surfaces are important to the health of plants as well as to people who consume fresh fruits and vegetables. However, the spatial distribution and organization of these immigrant bacteria on leaf surfaces are still poorly understood. To examine the spatial organization of these strains, two bacterial strains on tobacco leaves: (1) an indigenous strain, Pseudomonas stutzeri Nov. Y2011 labeled with green fluorescent protein, and (2) an immigrant strain Pantoea agglomerans labeled with cyan fluorescent protein isolated from pear, were studied. Under moist conditions, P. agglomerans cells quickly disappeared from direct observation by laser- scanning confocal microscopy, although elution results indicated that large amounts of live cells were still present on the leaves. Following exposure to desiccation stress, particles of cyan fluorescent protein-labeled P. agglomerans were visible within cracked aggregates of P. stutzeri Nov. Y2011. Detailed observation of sectioned aggregates showed that colonies of immigrant P. agglomerans were embedded within aggregates of P. stutzeri Nov. Y2011. Furthermore, carbon-resource partitioning studies suggested that these two species could coexist without significant nutritional competition. This is the first observation of an immigrant bacterium embedding within aggregates of indigenous bacteria on leaves to evade harsh conditions in the phyllosphere. 相似文献
344.
345.
采用美国EPA1623方法,研究滤池反冲洗水回用的贾第鞭毛虫和隐孢子虫泄漏问题.通过检测某水厂原水、出厂水和滤池反冲洗水中贾第鞭毛虫和隐孢子虫数量,表明该厂水源未受到贾第鞭毛虫和隐孢子虫的污染,但输送过程易造成水质的污染.滤池反冲洗水中只检出贾第鞭毛虫,出厂水中未检出贾第鞭毛虫和隐孢子虫,说明该厂滤池反冲洗水直接回用未造成"两虫"泄漏问题. 相似文献
346.
Alumina supported Pd catalyst(Pd/Al2O3) is active for complete oxidation of methane, while often suffers transient deactivation during the cold down process. Herein, heating and cooling cycle tests between 200 and 900 °C and isothermal experiments at 650 °C were conducted to investigate the influence of NOx on transient deactivation of Pd/θ-Al2O3 catalyst during the methane oxidation. It was found that the co-fed of NO alleviated transient d... 相似文献
347.
348.
349.
Yuliang Zhou Dong Zhang Ping Zhou Zhaoli Wang Pan Yang Juliang Jin Yi Cui Shaowei Ning 《Journal of the American Water Resources Association》2023,59(3):571-583
In univariate frequency analysis, the return period of an event has a one-to-one correspondence with its characteristic value, and the response of the hydraulic structure to hydrological load expressed by the hydrological event is monotonic. Thus, the design criteria of the hydraulic structure can be equivalently represented by the return period of the hydrological event, and consequently, design event-based design parameters evaluated have been widely used in practical engineering. However, the monotonic correspondence between the return period of the hydrological event and the response of the hydraulic structure does not exist in the multivariate context, and hydrological load with a larger joint return period does not always produce a more unsafe response. Misunderstandings of concepts of return periods of hydrological event, and estimation of hydrological design events usually take place in multivariate frequency analysis. This study theoretically derives the relations between different types of joint return periods, joint return period and its marginal return periods, the occurrence of bivariate extreme events and their return periods, and then the theoretical framework is tested. Results from the case contribute to the understanding of bivariate return periods of hydrological event, and the results demonstrate that design criteria cannot be equivalently represented by joint return periods of hydrological load, and design parameters of the hydraulic structure should not be determined by multivariate hydrological design events. 相似文献
350.