全文获取类型
收费全文 | 97087篇 |
免费 | 1293篇 |
国内免费 | 1546篇 |
专业分类
安全科学 | 3922篇 |
废物处理 | 3618篇 |
环保管理 | 14654篇 |
综合类 | 21922篇 |
基础理论 | 27252篇 |
环境理论 | 77篇 |
污染及防治 | 17712篇 |
评价与监测 | 5807篇 |
社会与环境 | 4307篇 |
灾害及防治 | 655篇 |
出版年
2022年 | 882篇 |
2021年 | 891篇 |
2020年 | 737篇 |
2019年 | 898篇 |
2018年 | 1287篇 |
2017年 | 1319篇 |
2016年 | 2326篇 |
2015年 | 1910篇 |
2014年 | 2657篇 |
2013年 | 9393篇 |
2012年 | 2558篇 |
2011年 | 3069篇 |
2010年 | 3513篇 |
2009年 | 3611篇 |
2008年 | 2581篇 |
2007年 | 2525篇 |
2006年 | 2739篇 |
2005年 | 2615篇 |
2004年 | 2870篇 |
2003年 | 2751篇 |
2002年 | 2296篇 |
2001年 | 2703篇 |
2000年 | 2240篇 |
1999年 | 1629篇 |
1998年 | 1414篇 |
1997年 | 1393篇 |
1996年 | 1528篇 |
1995年 | 1618篇 |
1994年 | 1506篇 |
1993年 | 1361篇 |
1992年 | 1360篇 |
1991年 | 1323篇 |
1990年 | 1284篇 |
1989年 | 1240篇 |
1988年 | 1081篇 |
1987年 | 1008篇 |
1986年 | 998篇 |
1985年 | 1078篇 |
1984年 | 1179篇 |
1983年 | 1173篇 |
1982年 | 1183篇 |
1981年 | 1102篇 |
1980年 | 953篇 |
1979年 | 945篇 |
1978年 | 827篇 |
1977年 | 728篇 |
1976年 | 643篇 |
1974年 | 626篇 |
1973年 | 651篇 |
1972年 | 650篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
J. B. Harcum Jim C. Loftis Robert C. Ward 《Journal of the American Water Resources Association》1992,28(3):469-478
ABSTRACT: The use of nonparametric tests for monotonic trend has flourished in recent years to support routine water quality data analyses. The validity of an assumption of independent, identically distributed error terms is an important concern in selecting the appropriate nonparametric test, as is the presence of missing values. Decision rules are needed for choosing between alternative tests and for deciding whether and how to pre-process data before trend testing. Several data pre-processing procedures in conjunction with the Mann-Kendall tau and the Seasonal Kendall test (with and without serial correlation correction) are evaluated using synthetic time series with generated serial correlation and missing data. A composite test (pre-testing for serial correlation followed by one of two trend tests) is evaluated and was found to perform satisfactorily. 相似文献
42.
43.
Kennedy N. Igbokwe 《中国人口.资源与环境(英文版)》2005,(1)
1 INTRODUCTIONIn the past, natural resources management initiatives havefocused on large but specific sector projects such as dams,reservoirs for water supply schemes, irrigation systems,crop production, at forestation, etc. Often these projectswere treated as technical and administrative issues ratherthan as a socio-economic and political one. However, thehigh social and environmental cost of such schemes haveled to a change of paradigm since the 1980s towards small-scale community projec… 相似文献
44.
可张孔曝气器曝气能耗试验研究 总被引:1,自引:0,他引:1
通过试验研究,总结出可张孔曝气阻力损失的影响因素,以优化产品的结构设计参数,降低产品在工程应用中的能耗,获取更好的经济效益。 相似文献
45.
The periodicity of fires in larch forests of Evenkia and their relationship with landscape elements have been studied. Cross-sections with “burns” in them caused by past fires have been analyzed in 72 test plots; the fire chronology encompassed the period from the 15th to the 20th century. The between-fire intervals (BFIs) have been calculated by two methods: (I) on the basis of burns alone and (II) on the basis of burns and the start of growth of the new generation of larch after the earliest fire. The BFI depends on local orographic features; it is 86 ± 11 (105 ± 12), 61 ± 8 (73 ± 8), 139 ± 17 (138 ± 18), and 68 ± 14 (70 ± 13) years for northeastern slopes, southwestern slopes, bogs, and flatlands, respectively. The mean BFIs calculated by methods I and II are 82 ± 7 and 95 ± 7 years, respectively. The permafrost horizon rises at a mean rate of 0.3 cm per year after a forest fire. It has been shown that the number of fires regularly peaks at periods of 36 and 82 years. There is also a temporal trend in fire frequency: the mean BFI was approximately 100 years in the 19th century and 65 years in the 20th century. 相似文献
46.
JHERIME L. KELLERMANN MATTHEW D. JOHNSON AMY M. STERCHO STEVEN C. HACKETT 《Conservation biology》2008,22(5):1177-1185
Abstract: Coffee farms can support significant biodiversity, yet intensification of farming practices is degrading agricultural habitats and compromising ecosystem services such as biological pest control. The coffee berry borer (Hypothenemus hampei) is the world's primary coffee pest. Researchers have demonstrated that birds reduce insect abundance on coffee farms but have not documented avian control of the berry borer or quantified avian benefits to crop yield or farm income. We conducted a bird‐exclosure experiment on coffee farms in the Blue Mountains, Jamaica, to measure avian pest control of berry borers, identify potential predator species, associate predator abundance and borer reductions with vegetation complexity, and quantify resulting increases in coffee yield. Coffee plants excluded from foraging birds had significantly higher borer infestation, more borer broods, and greater berry damage than control plants. We identified 17 potential predator species (73% were wintering Neotropical migrants), and 3 primary species composed 67% of migrant detections. Average relative bird abundance and diversity and relative resident predator abundance increased with greater shade‐tree cover. Although migrant predators overall did not respond to vegetation complexity variables, the 3 primary species increased with proximity to noncoffee habitat patches. Lower infestation on control plants was correlated with higher total bird abundance, but not with predator abundance or vegetation complexity. Infestation of fruit was 1–14% lower on control plants, resulting in a greater quantity of saleable fruits that had a market value of US$44–$105/ha in 2005/2006. Landscape heterogeneity in this region may allow mobile predators to provide pest control broadly, despite localized farming intensities. These results provide the first evidence that birds control coffee berry borers and thus increase coffee yield and farm income, a potentially important conservation incentive for producers. 相似文献
47.
48.
S. S. S. Sarma Saúl Avelino Rivera Fabiola Elizalde Hinojosa S. Nandini 《Russian Journal of Ecology》2007,38(5):353-362
We tested separately the effect of two taxonomically related rotifers (B. patulus and B. macracanthus) on the population dynamics of another species (A. fissa) at low (0.5 ×10 6) and high food levels (1.5 × 106 cells/ml of Chlorella vulgaris) using different inoculation densities (0–100%). We also quantified the impact of A. fissa on the two brachionid species. Regardless of the presence of the competing species, an increase in the availability of food
led to increase in the abundances of the three rotifers. The population growth of B. patulus, B. macracanthus, or A. fissa was affected negatively when cultured together with another species. An increase in the initial density of any one of the
competing species became advantageous to maintain a certain population size. At a low algal food level, B. patulus was able to suppress A. fissa more strongly than B. macracanthus. On the other hand, at a high food level, B. macracanthus suppressed the population of A. fissa more strongly than B. patulus. Peak population densities for A. fissa varied from about 150 to 1000 ind./ml, depending on food density and the presence of competitors. The rate of population
increase (r) of A. fissa, B. patulus, and B. macracanthus increased with an increase in food availability but decreased with increasing initial density of the competitor. Both Brachionus spp. experienced negative growth rates in the presence of A. fissa, especially at a high initial density of the latter.
Published in Russian in Ekologiya, 2007, Vol. 38, No. 5, pp. 381–390.
The article was submitted by the authors in English. 相似文献
49.
50.