全文获取类型
收费全文 | 16062篇 |
免费 | 149篇 |
国内免费 | 118篇 |
专业分类
安全科学 | 337篇 |
废物处理 | 650篇 |
环保管理 | 1889篇 |
综合类 | 3671篇 |
基础理论 | 3677篇 |
环境理论 | 7篇 |
污染及防治 | 4006篇 |
评价与监测 | 1021篇 |
社会与环境 | 1024篇 |
灾害及防治 | 47篇 |
出版年
2022年 | 112篇 |
2021年 | 130篇 |
2019年 | 106篇 |
2018年 | 204篇 |
2017年 | 194篇 |
2016年 | 316篇 |
2015年 | 246篇 |
2014年 | 363篇 |
2013年 | 1099篇 |
2012年 | 414篇 |
2011年 | 626篇 |
2010年 | 478篇 |
2009年 | 555篇 |
2008年 | 642篇 |
2007年 | 682篇 |
2006年 | 611篇 |
2005年 | 505篇 |
2004年 | 530篇 |
2003年 | 522篇 |
2002年 | 489篇 |
2001年 | 623篇 |
2000年 | 394篇 |
1999年 | 296篇 |
1998年 | 187篇 |
1997年 | 206篇 |
1996年 | 223篇 |
1995年 | 234篇 |
1994年 | 234篇 |
1993年 | 218篇 |
1992年 | 196篇 |
1991年 | 209篇 |
1990年 | 199篇 |
1989年 | 171篇 |
1988年 | 169篇 |
1987年 | 154篇 |
1986年 | 154篇 |
1985年 | 149篇 |
1984年 | 171篇 |
1983年 | 168篇 |
1982年 | 172篇 |
1981年 | 145篇 |
1980年 | 132篇 |
1979年 | 123篇 |
1978年 | 134篇 |
1977年 | 115篇 |
1976年 | 103篇 |
1975年 | 107篇 |
1974年 | 118篇 |
1971年 | 98篇 |
1967年 | 101篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
721.
In Europe, the use of direct methods using lysimeters for measuring water and solute flow in soils increased in recent years.
Large weighable lysimeters are best suitable for obtaining reliable data about seepage water quantity and quality. Field lysimeters
– lysimeters built in directly in agriculturally used areas – of high technical standard allow a precise determination of
the influence of different cropping systems on groundwater quality. They combine the advantages of true field conditions and
laboratory possibilities of varying parameters, handling and maintenance. Due to the specific needs of each application the
instrumentation varies. Based on general remarks on the advantages of precise weighing lysimeters four standardized lysimeter
configurations are presented. Beside the specific needs of design and setup of lysimeter stations, there is need to define
general requirements to enable comparable results based on standardized basic design and to reduce individual mistakes. 相似文献
722.
K. Pritsch D. Ernst F. Fleischmann S. Gayler T. E. E. Grams A. Göttlein W. Heller N. Koch H. Lang R. Matyssek J. C. Munch M. Olbrich H. Scherb S. Stich J. B. Winkler M. Schloter 《Water, Air, & Soil Pollution: Focus》2008,8(2):139-154
A lysimeter study was performed to monitor effects of elevated ozone on juvenile trees of Fagus sylvatica L. as well as on the plant–soil system. During a fumigation period over almost three growing seasons, parameters related
to plant growth, phenological development and physiology as well as soil functions were studied. The data analyses identified
elevated ozone to delay leaf phenology at early and to accelerate it at late developmental stages, to reduce growth, some
leaf nutrients (Ca, K) as well as some soluble phenolics (hydroxycinnamic acid derivatives, total flavonol glycosides). No
or very weak ozone effects were found in mobile carbon pools of leaves (starch, sucrose), and other phenolic compounds (flavans).
Altered gene expression related to stress and carbon cycling corresponded well with findings from leaf phenology and chemical
composition analyses indicating earlier senescence and oxidative stress in leaves under elevated ozone. Conversely in the
soil system, no effects of ozone were detected on soil enzyme activities, rates of litter degradation and lysimeter water
balances. Despite the fact that the three reported years 2003–2005 were climatically very contrasting including a hot and
dry as well as an extremely wet summer, and also mild as well as cold winters, the influence of ozone on a number of plant
parameters is remarkably consistent, further underlining the phytotoxic potential of elevated tropospheric ozone levels. 相似文献
723.
M. Gochfeld D. J. Gochfeld D. Minton B. G. Murray Jr P. Pyle N. Seto D. Smith J. Burger 《Environmental monitoring and assessment》1999,59(3):343-358
Levels of environmental pollutants are usually higher in mainland and coastal areas than in offshore or oceanic islands due to higher inputs from agricultural and industrial sources. Levels of heavy metals are usually higher in adult than in young birds, because they have had longer to accumulate metals in their tissues, and/or because they may eat larger, more contaminated, prey. We examined the levels of arsenic, cadmium, chromium, lead, manganese, mercury, and selenium in the adults and young of Bonin petrel (Pterodroma hypoleuca), Christmas shearwater (Puffinus nativitatis) and red-tailed tropicbird (Phaethon rubricauda) on Midway Atoll, and adult wedge-tailed shearwater (Puffinus pacificus) on Midway Atoll and on Manana Island (off Oahu) in the northern Pacific. All birds were analyzed individually except for Christmas Shearwater chicks where samples were pooled to obtain sufficient quantities for analysis. Significant (p<0.05) age-related differences were found for mercury, selenium, manganese and chromium in Bonin petrels, for selenium and mercury in Christmas shearwaters, and for chromium and mercury in Red-tailed Tropicbirds. Lead approached significance for all three species. Adults had higher levels than young except for chromium and manganese in the petrels and arsenic in all three species. There were significant interspecific differences in concentrations of all metals except arsenic for the adults nesting on Midway. Christmas shearwaters had the highest levels of all metals except mercury and chromium. Bonin petrels, the smallest species examined, had mercury levels that were over three times higher than any of the adults of the other three species. For wedge-tailed shearwaters, levels of chromium and lead were significantly higher, and manganese and selenium were lower on Midway than Manana. Knowledge of the foraging ranges and habits of these far-ranging seabirds is inadequately known, but does not currently explain the observed differences among species. We could not find a consistent pattern of differences between the burrow nesting species (Bonin petrel, Wedge-tailed shearwater) and the surface nesting tropicbirds. There was no consistent pairwise correlation between any metals across all species. 相似文献
724.
H. T. Schreuder R. Czaplewski R. G. Bailey 《Environmental monitoring and assessment》1999,56(3):269-291
A forest ecological inventory and monitoring system combining information derived from maps and samples is proposed based on ecosystem regions (Bailey, 1994). The system extends the design of the USDA Forest Service Region 6 Inventory and Monitoring System (R6IMS) in the Pacific Northwest of the United States. The key uses of the information are briefly discussed and expected results are illustrated with examples. The system is flexible, allowing regions based on ecological considerations to be modified. Sampling intensities that are affordable are likely to be insufficient to provide meaningful estimates for key parameters relating to rare and endangered species, watersheds, and other ecological units. Methods are proposed for collecting additional information in follow-up surveys and combining it with relevant information obtained in R6IMS. Near-continuous information on weather and possible pollution variables recorded by instruments at sampling sites is needed to develop meaningful models to understand what is happening in the ecoregions. R6IMS and the proposed additions constitute a dynamic system which will be modified further as data are analyzed. 相似文献
725.
Donald G. Miller III. 《Behavioral ecology and sociobiology》1998,43(2):95-103
This study investigated the consequences of communal gall induction on individual and group fitness in the aphid Tamaliacoweni. The possibilities that kin discrimination and foundress density are factors favoring communal gall occupation were examined.
Clonally produced aphid foundresses were collected to create two treatments: clonal groups and groups of less closely related
individuals. These were confined on suitable host plant tissue to compare their respective propensities towards communal behavior.
There were no significant differences in the frequencies of communal gall occupation; therefore, active kin discrimination
by T.coweni foundresses apparently does not play a role in their communal behavior, within the context of this experiment. In a second
experiment, aphid foundress density on the host plant was manipulated in three treatments and was correlated with the frequency
of communal gall occupation. Individual fitness was inversely related to the mean number of foundresses per gall. These results
suggest that communal gall occupation does not necessarily represent mutual cooperation but may instead be the outcome of
competition for limited gall sites on the host plant. However, natural selection at the clonal level may favor communal gall
occupation under the conditions of resource limitation and high within-group relatedness.
Received: 26 September 1997 / Accepted after revision: 28 March 1998 相似文献
726.
Jacobus C. Biesmeijer Mark G. L. van Nieuwstadt Saskia Lukács Marinus J. Sommeijer 《Behavioral ecology and sociobiology》1998,42(2):107-116
Social insect foragers have to make foraging decisions based on information that may come from two different sources: information
learned and memorised through their own experience (“internal” information) and information communicated by nest mates or
directly obtained from their environment (“external” information). The role of these sources of information in decision-making
by foragers was studied observationally and experimentally in stingless bees of the genus Melipona. Once a Melipona forager had started its food-collecting career, its decisions to initiate, continue or stop its daily collecting activity
were mainly based upon previous experience (activity on previous days, the time at which foraging was initiated the day(s)
before, and, during the day, the success of the last foraging flights) and mediated through direct interaction with the food
source (load size harvested and time to collect a load). External information provided by returning foragers advanced the
start of foraging of experienced bees. Most inexperienced bees initiated their foraging day after successful foragers had
returned to the hive. The start of foraging by other inexperienced bees was stimulated by high waste-removal activity of nest
mates. By experimentally controlling the entries of foragers (hence external information input) it was shown that very low
levels of external information input had large effect on the departure of experienced foragers. After the return of a single
successful forager, or five foragers together, the rate of forager exits increased dramatically for 15 min. Only the first
and second entry events had large effect; later entries influenced forager exit patterns only slightly. The results show that
Melipona foragers make decisions based upon their own experience and that communication stimulates these foragers if it concerns the
previously visited source. We discuss the organisation of individual foraging in Melipona and Apis mellifera and are led to the conclusion that these species behave very similarly and that an information-integration model (derived
from Fig. 1) could be a starting point for future research on social insect foraging.
Received: 16 April 1997 / Accepted after revision: 30 August 1997 相似文献
727.
An Ecology-Based Method for Defining Priorities for Large Mammal Conservation: The Tiger as Case Study 总被引:2,自引:0,他引:2
728.
729.
A Systematic Test of an Enterprise Strategy for Community-Based Biodiversity Conservation 总被引:6,自引:0,他引:6
N. Salafsky H. Cauley G. Balachander B. Cordes J. Parks C. Margoluis S. Bhatt C. Encarnacion D. Russell R. Margoluis 《Conservation biology》2001,15(6):1585-1595
Abstract: A commonly held belief is that if people can benefit financially from enterprises that depend on nearby forests, reefs, and other natural habitats, then they will take action to conserve and sustainably use them. The Biodiversity Conservation Network brought together conservation and development organizations and local communities to systematically test this hypothesis across 39 conservation project sites in Asia and the Pacific. Each project implemented one or more community-based enterprises such as setting up an ecotourism lodge, distilling essential oils from wild plant roots, producing jams and jellies from forest fruits, harvesting timber, or collecting marine samples to test for pharmaceutical compounds. Each project team collected the biological, enterprise, and social data necessary to test the network's hypothesis. We present the results of this test. We found that a community-based enterprise strategy can lead to conservation, but only under limited conditions and never on its own. We summarize the specific conditions under which an enterprise strategy will and will not work in a decision chart that can be used by project managers to determine whether this strategy might make sense at their site. We also found that an enterprise strategy can be subsidized and still create a net gain that pays for conservation. Based on our experiences, we recommend developing "learning portfolios" that combine action and research to test other conservation strategies. 相似文献
730.