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   52827篇
  免费   573篇
  国内免费   432篇
安全科学   1651篇
废物处理   2276篇
环保管理   7208篇
综合类   9306篇
基础理论   13929篇
环境理论   21篇
污染及防治   12961篇
评价与监测   3343篇
社会与环境   2801篇
灾害及防治   336篇
  2022年   401篇
  2021年   469篇
  2019年   385篇
  2018年   675篇
  2017年   726篇
  2016年   1124篇
  2015年   841篇
  2014年   1273篇
  2013年   4238篇
  2012年   1585篇
  2011年   2178篇
  2010年   1748篇
  2009年   1854篇
  2008年   2217篇
  2007年   2222篇
  2006年   1994篇
  2005年   1714篇
  2004年   1667篇
  2003年   1651篇
  2002年   1540篇
  2001年   1879篇
  2000年   1333篇
  1999年   829篇
  1998年   634篇
  1997年   675篇
  1996年   708篇
  1995年   805篇
  1994年   730篇
  1993年   665篇
  1992年   668篇
  1991年   673篇
  1990年   655篇
  1989年   641篇
  1988年   585篇
  1987年   516篇
  1986年   489篇
  1985年   508篇
  1984年   562篇
  1983年   522篇
  1982年   575篇
  1981年   502篇
  1980年   419篇
  1979年   439篇
  1978年   405篇
  1977年   352篇
  1976年   324篇
  1975年   324篇
  1974年   353篇
  1973年   371篇
  1972年   345篇
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
51.
52.
Mosaicism for trisomy 13 and triploidy was detected by amniocentesis performed at 18 weeks' gestation because of fetal anomalies. Pregnancy continued and a live-born male was delivered vaginally at 37 weeks. The infant had features common to both trisomy 13 and triploidy: intrauterine growth retardation (IUGR), small abnormal ears, cleft palate, and a small jaw. In addition, he had complete cutaneous syndactyly of fingers 3 and 4 and partial syndactyly of the toes, as seen in triploidy. Mixoploidy for trisomy 13 and triploidy was confirmed postnatally in blood, skin, and placenta. Examination of chromosome heteromorphisms and DNA markers suggested the presence of two maternal contributions in the triploid cell line. In addition, the extra chromosome 13 in the trisomic cell line was derived from the mother. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
53.
54.
Energy efficiency is often stated to be the most cost-effective measure for satisfying our energy demand with minimal environmental damage. However, the potential energy savings attainable in 'the real world' are frequently overestimated, as is shown in an industrial case study of the glass industry. Nevertheless, there are significant energy savings to be realized, and the role of new technologies in this is important. However, the key to the effective use of new technology for improved energy efficiency is good management and. for best effect, it must be integrated into the normal resource management activities of a company.  相似文献   
55.
全球粮食生产的预测问题   总被引:1,自引:0,他引:1  
本文讨论了全球粮食生产体系能力预测模型的研发问题,文章特别对影响粮食生产的各种因素进行了鉴定和分析,并且对它们的相对影响和可预测性进行了估计。  相似文献   
56.
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   
57.
As part of a programme to characterize floating anthropogenic debris in the aquatic environment, the US Environmental Protection Agency (EPA) conducted 18 field surveys in the harbours of major metropolitan cities of the east, west, and Gulf coasts of the United States and the Mid-Atlantic Bight. the surveys were designed to provide information on the types, relative amounts, and distributions of aquatic debris in different geographic regions of the United States. Neuston nets (0.33 mm mesh) were used to collect surface debris during outgoing tides on two or three consecutive days in selected areas of each city. After each net tow, the debris, which ranged in size from small resin pellets to large plastic sheeting pieces, was identified, categorized, and counted. the data are being used to qualitatively characterize aquatic debris in coastal metropolitan areas, to examine potential regional variations, and to tentatively identify potential sources.  相似文献   
58.
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   
59.
This paper is concerned with developing a model for group decision making under multiple criteria. The multiple criteria group decision making (MCGDM)problem involves a set of feasible land use patterns that are evaluated on the basis of multiple, conflicting and noncommensurate criteria by a group of individuals. The model integrates the Analytic Hierarchy Process (AHP) and an integer mathematical programming method. The former provides a tool for structuring the decision problem and determining land suitability for different socio-economicactivities (the uses of land), the latter is used to identify the land use pattern that maximizes consensus among interest groups. The model is used to analyze environmental conflict over land resource allocation in the Cape Region of Mexico.  相似文献   
60.
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