首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   52263篇
  免费   603篇
  国内免费   642篇
安全科学   1773篇
废物处理   2460篇
环保管理   6764篇
综合类   8362篇
基础理论   13655篇
环境理论   26篇
污染及防治   13304篇
评价与监测   3614篇
社会与环境   3219篇
灾害及防治   331篇
  2023年   233篇
  2022年   546篇
  2021年   594篇
  2020年   389篇
  2019年   482篇
  2018年   844篇
  2017年   878篇
  2016年   1298篇
  2015年   983篇
  2014年   1495篇
  2013年   4260篇
  2012年   1828篇
  2011年   2464篇
  2010年   1968篇
  2009年   1985篇
  2008年   2416篇
  2007年   2415篇
  2006年   2136篇
  2005年   1839篇
  2004年   1716篇
  2003年   1768篇
  2002年   1596篇
  2001年   1941篇
  2000年   1377篇
  1999年   843篇
  1998年   611篇
  1997年   624篇
  1996年   635篇
  1995年   753篇
  1994年   709篇
  1993年   597篇
  1992年   636篇
  1991年   622篇
  1990年   614篇
  1989年   571篇
  1988年   504篇
  1987年   450篇
  1986年   414篇
  1985年   425篇
  1984年   467篇
  1983年   444篇
  1982年   463篇
  1981年   387篇
  1980年   310篇
  1979年   342篇
  1978年   299篇
  1977年   228篇
  1975年   247篇
  1973年   232篇
  1972年   243篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
51.
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   
52.
53.
54.
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   
55.
56.
57.
Male phenotype associated with a 45,X karyotype is an infrequent finding. We present a case diagnosed prenatally on amniocentesis performed for maternal age. The male phenotype was associated with a translocation of a distal part of Yp including the pseudoautosomal SHOX gene and SRY gene on the short arm of a chromosome 21. By DNA analysis we could show that the X chromosome was of maternal origin and that the breakpoint was in interval 3 of the Y chromosome. Mechanisms and genetic counselling are discussed based on a review of published cases of 45,X and XX males. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
58.
Quick fix. Putting out firs. Do it over. Fix it again. Bottlenecks. Come back to it later. Out of stock. Back order. Not what we ordered. Is that the best you can do? It's the contractor's fault. Not within specs. Defective. Nobody's perfect. Lost in the system. Over budget. Delayed. Late penalities. Fines.  相似文献   
59.
The haematotoxicity of technical hexachlorocyclohexane (HCH) (1000 ppm) was investigated in male albino rats fed with diet free of vitamin A or containing vitamin A at 2000 or 10(5) I.U./kg. Assessment of HCH-induced haematotoxicity at the end of the 7 weeks feeding period was done on the basis of haemoglobin content, total count of red blood cells and white blood cells and the differential counts of the white blood cells as well as by parameters such as packed cell volume, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin content, prothrombin time and clotting time. In the rats fed with vitamin A-free diet containing HCH, significant reductions were noticed in the total white blood cells count, clotting time and prothrombin time indicating severe haematotoxicity. Differential count of the white blood cells of these rats revealed a non-significant reduction in the lymphocyte count. The only indication of haematotoxicity caused by hexachlorocyclohexane in the vitamin A supplemented rats was a slight but statistically significant reduction of the total count of white blood cells. These results demonstrate that the haematotoxicity of hexachlorocyclohexane in the rats is enhanced by vitamin A-deficiency and its supplementation particularly in excess but not at hypervitaminotic level is protective against the toxicity.  相似文献   
60.
Although most research has focussed on inorganic nutrient forms of nitrate (NO-3) and phosphorus (PO34) in runoff and receiving waters, nitrogen loss from agricultural land can also occur in organic and ammonium-nitrogen form; phosphorus losses, although often dominated by particulate transport, may occur in soluble organic and inorganic form. Furthermore, fluxes between different species may take place during transport from the land to the stream and as a result of in-stream, in-river or in-lake transformations. Knowledge of the spatial and temporal variation in all nitrogen species and phosphorus fractions in a drainage basin is therefore essential if the wider environmental significance of elevated nutrient concentrations in natural waters are to be assessed. This paper reviews recent work on N and P losses from agricultural land and presents some results from two intensive agricultural catchments: Slapton, Devon and the river Windrush catchment in the Cotswolds.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号