全文获取类型
收费全文 | 332篇 |
免费 | 27篇 |
国内免费 | 82篇 |
专业分类
安全科学 | 7篇 |
废物处理 | 18篇 |
环保管理 | 52篇 |
综合类 | 278篇 |
基础理论 | 44篇 |
污染及防治 | 26篇 |
评价与监测 | 8篇 |
社会与环境 | 8篇 |
出版年
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 17篇 |
2018年 | 8篇 |
2017年 | 17篇 |
2016年 | 16篇 |
2015年 | 11篇 |
2014年 | 6篇 |
2013年 | 22篇 |
2012年 | 29篇 |
2011年 | 23篇 |
2010年 | 18篇 |
2009年 | 15篇 |
2008年 | 18篇 |
2007年 | 22篇 |
2006年 | 25篇 |
2005年 | 30篇 |
2004年 | 23篇 |
2003年 | 18篇 |
2002年 | 11篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 11篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有441条查询结果,搜索用时 62 毫秒
51.
A simple method for the quantitative gradient analysis of a xerotermic forest-margin ecotone is described. In this method, the mean value of the coefficient of similarity between all plots of the transect is used for estimating the rate of changes in species composition. Changes in the phytosociological spectrum are analyzed. The method adequately reflects trends in the displacement of forest species by forest-margin, steppe, and meadow species. 相似文献
52.
Over the last few years, many studies have presented the real options valuation (ROV) as a promising technique of valuing natural resource investments under conditions of uncertainty. Apart from the common conclusion that the ROV is better than the conventional net present value (NPV) method in integrating the value of management flexibility and proper handling of cash flows risk, there is a lack of procedures for testing the usefulness and advantages of the ROV over the static NPV method in practice. Arguably, it is not yet clear whether the ROV can deal with the complexity of mining projects and whether it can really be applied to make decisions that improve project value. 相似文献
53.
By 2009, Ghana was the second-ranked African producer after South Africa, and had become the world's ninth largest producer of gold, at some 3.8% of global production, up from 2.6% five years earlier. Gold production volumes and revenues rose significantly over the decade from 2000. Yet gold mining tends to be perceived negatively in Ghana, and is seen as providing far less than it should in terms of public revenue, employment, skills development and spillovers, and localised economic development. Gold mining is often depicted as having an enclave status, disconnected and isolated from the rest of the economy. In contrast, the research findings here demonstrate that after a period of strong investment and growth, gold mining can no longer be viewed as an enclave activity: it is in fact more deeply linked into the Ghanaian economy than hitherto understood, through a set of as yet under-researched but promising economic linkages, notably backward linkages, which can potentially be strengthened by policy and support measures. 相似文献
54.
55.
56.
以Cu-TEPA为模板剂原位水热合成一系列具有优良deNOx特性的Cu-SSZ-13/堇青石整体式催化剂.为进一步改善其氨的选择性催化还原氮氧化物的活性,在制备过程中添加HF对原位制备Cu-SSZ-13/堇青石整体式催化剂进行改性.利用XRD、SEM、XPS、BET、ICP-AES等对样品进行了表征.结果表明,当nHF/nAl在0.015—0.0375时,晶化72 h的Cu-SSZ-13/堇青石表现出了优异的脱硝性能和抗老化性能,其最大转化率为99.8%,NOx转化率保持在90%以上的最宽活性温度窗口为280—640℃,而无HF的新鲜样品的NOx转化率保持在90%以上的活性温度窗口为300—580℃;720℃老化50 h处理后,nHF/nAl=0.015—0.0375样品的NOx转化率保持在90%以上的最宽活性温度窗口为360—520℃,未添加HF的老化样品相应的活性温度窗口为400—500℃.无论新鲜还是老化,nHF/nAl=0.015—0.0375样品在低温段200—300℃和高温段500—700℃的NOx转化率基本都大于未添加HF的样品.结合表征结果,在催化剂原位水热合成过程中HF的加入既提高了样品的相对结晶度和负载量,又增大了样品的比表面积和比孔容,且提高了Cu-SSZ-13/堇青石骨架结构的稳定性,进而在一定程度上改善了Cu-SSZ-13/堇青石的高温脱硝活性和水热稳定性. 相似文献
57.
58.
Sonia Rombout Daniel Sartenaer Benoît Parmentier Christian Dugauquier Yves Gillerot 《黑龙江环境通报》2004,24(10):822-827
We present a case of de novo trisomy of distal 19q diagnosed prenatally by cytogenetics and FISH analysis. The autopsy performed after termination of the pregnancy showed major internal and external malformations that are associated with this chromosome abnormality. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
59.
Prenatal diagnosis of 5p deletion syndrome, or cri du chat, following an abnormally low measurement of a screening of serum human chorionic gonadotrophin (hCG), is reported. Karyotyping following amniocentesis revealed a terminal deletion in the short arm of one chromosome 5. The pregnancy was electively terminated. 5p deletion syndrome has been described with abnormally high hCG levels and normal hCG levels. This is the first report of its association with abnormally low levels. The association between chromosomal abnormalities and hCG is discussed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
60.
Agnès Guichet Stéphane Triau Catherine Lépinard Chantal Esculapavit Florence Biquard Philippe Descamps Férechté Encha-Razavi Dominique Bonneau 《黑龙江环境通报》2004,24(10):828-832
We report an interstitial deletion of chromosome 3q26-q28 in a fetus in which anophthalmia had been detected prenatally. FISH analysis, using BAC clones encompassing the SOX2 locus, showed that SOX2 gene was involved in the chromosomal breakpoint of the deletion. This case confirms that haploinsufficiency for SOX2 plays a crucial role in human eye development and emphasizes the necessity of careful chromosomal analysis, including FISH analysis of the 3q region, in case of prenatal discovery of anophthalmia. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献