全文获取类型
收费全文 | 253136篇 |
免费 | 16236篇 |
国内免费 | 36075篇 |
专业分类
安全科学 | 23733篇 |
废物处理 | 11656篇 |
环保管理 | 29181篇 |
综合类 | 103617篇 |
基础理论 | 47755篇 |
环境理论 | 211篇 |
污染及防治 | 50549篇 |
评价与监测 | 16620篇 |
社会与环境 | 15044篇 |
灾害及防治 | 7081篇 |
出版年
2024年 | 681篇 |
2023年 | 3281篇 |
2022年 | 9021篇 |
2021年 | 9052篇 |
2020年 | 8692篇 |
2019年 | 6816篇 |
2018年 | 7928篇 |
2017年 | 9267篇 |
2016年 | 9268篇 |
2015年 | 9259篇 |
2014年 | 11453篇 |
2013年 | 21000篇 |
2012年 | 16165篇 |
2011年 | 18133篇 |
2010年 | 15844篇 |
2009年 | 15618篇 |
2008年 | 16009篇 |
2007年 | 15694篇 |
2006年 | 14666篇 |
2005年 | 11363篇 |
2004年 | 8764篇 |
2003年 | 7743篇 |
2002年 | 6851篇 |
2001年 | 6244篇 |
2000年 | 5293篇 |
1999年 | 3626篇 |
1998年 | 2455篇 |
1997年 | 2227篇 |
1996年 | 2256篇 |
1995年 | 2322篇 |
1994年 | 2045篇 |
1993年 | 1515篇 |
1992年 | 1535篇 |
1991年 | 1367篇 |
1990年 | 1255篇 |
1989年 | 1147篇 |
1988年 | 1014篇 |
1987年 | 906篇 |
1986年 | 859篇 |
1985年 | 871篇 |
1984年 | 896篇 |
1983年 | 824篇 |
1982年 | 918篇 |
1981年 | 818篇 |
1980年 | 627篇 |
1979年 | 686篇 |
1978年 | 585篇 |
1977年 | 513篇 |
1975年 | 467篇 |
1974年 | 461篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
541.
542.
543.
The coastal water of northeast Taiwan island, called 'Yin-Yang Hai' for its distinct yellow colour compared with blue offshore water, was investigated from 1989 to 1990 by the authors. Biological study showed the dominant species of plankton to be Copepoda, Cladocera, planktonic eggs and Diatoma. Dominant species of benthos were young crabs, Amphipoda and Annelida, with Amphipoda usually occurring in heavily polluted areas. Heavy metal data showed that the concentration of copper was high. the copper and iron concentration in algae of the intertidal zone was also high. the concentrations of iron and copper in inshore water were also higher than in offshore water. By comparison of the pH and salinity distribution of this area, we conclude that this coastal water has been polluted by acid waste water from coastal industry. the suspended solids concentration in sea water is high. Flocculation occurring at the boundary of fresh and saline water might be a reason for the distinct yellow colour of the water of this area. Further study is required. 相似文献
544.
关中地区飑线天气的预测及灾害对策探讨 总被引:1,自引:0,他引:1
对1961~1990年发生在陕西省关中地区的飑线天气及其灾害进行了统计分析,并从天气形势背景方面对飑线的发生发展进行了研究和分析,同时就飑线的预测和防灾对策进行了探讨。 相似文献
545.
This paper reports the first investigation of risk perception by workers on offshore oil and gas installations on the UK Continental Shelf, following changes in offshore safety legislation in the wake of the Piper Alpha disaster in 1988. The Offshore Safety Case regulations (Health and Safety Executive, 1992, A Guide to the Offshore Installations (Safety Case) Regulations) put the onus on the operator to identify the major hazards and to reduce the risks to As Low As is Reasonably Practicable (ALARP). The regulations specifically state that Quantitative Risk Assessments (QRA) must be used when preparing the Safety Case. However, people do not use QRA when making everyday judgements about risk; they make subjective judgements known as risk perceptions, which are influenced by a number of different factors. This study was designed to complement the extensive QRA calculations that have already been carried out in the development of Safety Cases. The aim was to measure subjective risk perception in offshore personnel and examine how this relates to the more objective risk data available, namely accident records and QRA calculations. This paper describes the Offshore Risk Perception Questionnaire developed to collect the data and reports on UK offshore workers' perceptions of the risks associated with major and minor hazards, work tasks and other activities aboard production platforms. 相似文献
546.
Red pine (Pinus resinosa Ait.) is rare (< 15 000 mature trees) in Newfoundland and is known from only 22 locations in the central region. Red pine occupies 3 major site types in Newfoundland: 1) red pine on medium-textured sands (RP1), 2) red pine on coarse-textured glaciofluvial deposits (RP2), and 3) red pine on Folisols over bedrock (RP3). The succession of red pine site types after cutting is from red pine to Kalmia-black spruce (Picea mariana (Mill.) B.S.P.) for RP1, and to Cladonia-Kalmia-black spruce for types RP2 and RP3. Succession after fire is usually to the pre-fire type, but this depends on the severity of the fire.Although occupying a relatively poor site, red pine at 60–70 years reaches heights in excess of 18 m, dbh in excess of 40 cm, and individual tree volumes greater than 1 m3 were recorded in 75 stemanalyzed fire-killed trees. Black spruce on that same site produces less than one-third that volume in 60 years. Merchantable volume of 140–280 m3 ha-1 were recorded i.e., Canada Land Inventory (CLI) forest capability class 5 and class 4 ratings. This raises the CLI rating two capability classes if red pine were occupying these poor quality sites over black spruce. In terms of nutrition, even the best growing red pine are nitrogen (N) deficient as shown by foliar analysis. All natural stands have foliar N concentrations below 1.3% which is the critically low level shown in the literature. Immediately after fire, foliar concentrations reach this level but are usually about 1% or less. Most other nutrients are low but are within the generally reported adequate levels in testing for P, K, Ca and Mg.Fire influences soil nutrient availability as pH increases in the RP1 type. Burning temperature also affects soil pH and the understory vegetation. The RP2 type loses more N in hotter burns on this site type and more N is tied up in these ortstein hardpan soils. The pattern of regeneration following wildfire is related to slope, density, age and species mixture of the stand as well as the thickness and composition of the duff layer. 相似文献
547.
This text describes two different experiences of co-operation between unionists and researchers that resulted in writing of a book. We emphasize their similarities and differences and discuss the importance of these experiences in the dynamics of research and training in Ergonomics. 相似文献
548.
549.
Supportive Breeding and Variance Effective Population Size 总被引:2,自引:0,他引:2
The practice of supporting weak, wild populations through release of individuals bred in captivity is becoming an increasingly important conservation measure. A frequently recommended form of such breeding-release activity refers to supportive breeding: a fraction of the target population is brought into captivity for reproduction, and the resulting progeny are released to mix with the wild segment of the population. We derived an expression for the variance effective size of a population managed through supportive breeding and discuss its relationship to previously published equations that are based on the assumption of random mating. We show that the effect of supportive breeding may be quite different on the inbreeding and the variance effective sizes. Whereas supportive breeding always results in a reduction of the inbreeding effective number, the variance effective number may either decrease, increase, or remain unchanged. We discuss these observations in relation to conservation management and suggest some general guidelines for supportive breeding situations. Our recommendations include making a distinction between inbreeding and variance effective numbers; taking particular care when dealing with organisms with high reproductive potential; assuring that the amount of drift be no larger than it would be without supportive breeding; and focusing primarily on the variance effective size of a population-that is, on the effective number directly related to the rate of loss of gene diversity. 相似文献
550.