全文获取类型
收费全文 | 49553篇 |
免费 | 453篇 |
国内免费 | 354篇 |
专业分类
安全科学 | 1350篇 |
废物处理 | 2528篇 |
环保管理 | 6623篇 |
综合类 | 7117篇 |
基础理论 | 13577篇 |
环境理论 | 11篇 |
污染及防治 | 11831篇 |
评价与监测 | 3689篇 |
社会与环境 | 3362篇 |
灾害及防治 | 272篇 |
出版年
2022年 | 337篇 |
2021年 | 410篇 |
2020年 | 262篇 |
2019年 | 348篇 |
2018年 | 1893篇 |
2017年 | 1834篇 |
2016年 | 2022篇 |
2015年 | 797篇 |
2014年 | 1093篇 |
2013年 | 3349篇 |
2012年 | 1720篇 |
2011年 | 2910篇 |
2010年 | 2075篇 |
2009年 | 1974篇 |
2008年 | 2567篇 |
2007年 | 2837篇 |
2006年 | 1666篇 |
2005年 | 1426篇 |
2004年 | 1459篇 |
2003年 | 1415篇 |
2002年 | 1352篇 |
2001年 | 1593篇 |
2000年 | 1102篇 |
1999年 | 664篇 |
1998年 | 539篇 |
1997年 | 529篇 |
1996年 | 552篇 |
1995年 | 639篇 |
1994年 | 589篇 |
1993年 | 508篇 |
1992年 | 539篇 |
1991年 | 513篇 |
1990年 | 510篇 |
1989年 | 502篇 |
1988年 | 434篇 |
1987年 | 373篇 |
1986年 | 362篇 |
1985年 | 366篇 |
1984年 | 416篇 |
1983年 | 403篇 |
1982年 | 409篇 |
1981年 | 361篇 |
1980年 | 273篇 |
1979年 | 315篇 |
1978年 | 269篇 |
1977年 | 226篇 |
1975年 | 231篇 |
1974年 | 221篇 |
1973年 | 243篇 |
1972年 | 242篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Certain hydrothermal vent invertebrates, e.g. Riftia pachyptila and Calyptogena magnifica, are clearly established as harboring dense populations of chemoautotrophic sulfur bacteria in specialized tissues. By contrast, the physiological characteristics of the abundant intracellular gill symbiont of the vent mussel Bathymodiolus thermophilus have been questioned. The low activities of enzymes diagnostic for CO2 fixation (Calvin cycle) and for sulfur-driven energy generation, as measured by other investigators, have been attributed to bacterial contamination of the gill surface. Based on research at the Galápagos Rift hydrothermal vents in 1988 and subsequent laboratory experiments, the current study confirms that the B. thermophilus symbiont is a psychrophile for which thiosulfate and sulfide stimulate CO2 fixation. It strongly indicates that the symbiont is a chemoautotroph by establishing the following: (1) Sulfide and thiosulfate can stimulate CO2 fixation by partially purified symbionts by up to 43-fold and 120-fold, respectively; (2) the ribulose-1,5-bisphosphate carboxylase/oxygenase activity of the symbiont is sufficient to account for its sulfide- or thiosulfate-stimulated CO2 incorporation; (3) the symbiont's molar growth yield on thiosulfate, as judged by CO2 incorporation, is indistinguishable from that of free-living chemoautotrophs. Due to the high protein-degrading activity of B. thermophilus gill lysate, it is also suggested that host lysis of symbionts plays a more important role in the nutrition of the vent mussel than in R. pachyptila or C. magnifica, for which no comparable protein-degrading activity was found. 相似文献
53.
D. K. A. Barnes 《Marine Biology》1995,121(3):555-563
Photographs were taken every 0.5 m along three transects of 5.5 m length on shallow rock faces at Signy Island, Antarctica, during the austral summer of 1991/1992. The percentage cover of substratum ranged from 0 to 100% and the colonising communities included representatives of ten phyla. The zone from mean low-water neap level to 1.5 m depth was mostly devoid of organisms as a result of the seasonal formation of the encrusting ice foot. Coralline and macroalgae dominated from 2 to 3 m, and animal groups from 3.5 to 5.5 m. Bryozoans, and to a lesser extent sponges, were the most abundant animal phyla. Within the bryozoans a succession of colonisation of different species was observed, the most abundant two of which occupied >80% of substratum in places. Substratum type seemed to be the main factor influencing community development in the shallow sublittoral at Signy Island, although ice impact prevents community development in the top 1.5 m and limits it over the rest of the transect down to 5.5 m. Depth and profile of substratum also influenced communities within this depth range (particularly taxonomic composition). 相似文献
54.
Fragile X syndrome is the most common cause of familial mental retardation. The most common mutation is expansion of a triplet (CGG)n repeat in the 5′ untranslated region of the FMR1 gene on Xq27.3. The expansion is refractory to PCR due to preferential amplification of the smaller allele in heterozygous cells and the high GC content of the repeat and surrounding sequences. Direct detection of the normal parental alleles in preimplantation embryos has been used for preimplantation genetic diagnosis (PGD) of this disorder. However, this approach is only suitable for approximately 63% of couples due to the heterozygosity of the repeat in the normal population. As an alternative we investigated the use of polymorphic markers flanking the mutation to track the normal and premutation carrying maternal chromosomes in preimplantation embryos. Using a panel of 11 polymorphisms, six (CA)n repeats and five single nucleotide polymorphisms, diagnosis was developed for 90% of referred couples. Multiplex amplification of informative markers was tested in 300 single buccal cells from interested couples with efficiency and allele drop out (ADO) rates ranging from 69% to 96% and 6% to 18%, respectively. Use of this approach is accurate and applicable to a larger number of patients at risk of transmitting fragile X to their offspring. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
55.
D Heinevetter H J Lewerenz R Plass R Macholz 《Journal of environmental science and health. Part. B》1985,20(5):539-558
In vitro investigations of the influence of lindane and its metabolites were performed on microsomal and mitochondrial ATPases from liver, kidney and brain of rat and mouse. The microsomal Na+-K+-ATPases in rat liver were inhibited by the tested substances. An increase of activity was observed only with 2.5 X 10(-5) M gamma-HCH. Effects on the microsomal Na+-K+-ATPase from kidney and brain of rat were also indicated. The mitochondrial enzyme in rat liver was stimulated by all the compounds tested at concentrations of 10(-4) M - 10(-2) M. The effects on mitochondrial enzymes from kidney and brain varied in dependence on the tested substances. In the microsomes and mitochondria of mouse an influence on the Na+-K+-ATPases similar to the effects on the preparations from organs of rat was evident. 相似文献
56.
The purpose of this paper is to analyse the recent behaviour of the US zinc processing industry and the impact of US government policies on it. The first section of the paper is a discussion on the basic structure and conditions of the US zinc processing industry since 1950 and how they have changed. The discussion contains a general presentation of the US zinc market, a detailed look at the behaviour of individual primary zinc processing plants in the USA, Canada, Japan and Western Europe and an analysis of US government policies and their impacts on the US zinc industry. The second section of the paper is a discussion of the factors that have contributed to the decline in US zinc processing capacity and the type of government policy that should be followed in response. 相似文献
57.
58.
59.
A. V. Krylov 《Russian Journal of Ecology》2004,35(5):316-323
The abundance and trophic structure of zooplankton along the longitudinal profile of two typical rivers in the Yaroslavl sector of the Volga region are determined by anthropogenic and zoogenic factors. The distribution of zooplankton under the influence of these factors is described by the concept of patch dynamics. The abundance of zooplankton reaches the highest values in the ameliorated upper reaches of rivers and in beaver ponds. 相似文献
60.