全文获取类型
收费全文 | 5035篇 |
免费 | 91篇 |
国内免费 | 48篇 |
专业分类
安全科学 | 169篇 |
废物处理 | 168篇 |
环保管理 | 899篇 |
综合类 | 805篇 |
基础理论 | 1285篇 |
环境理论 | 13篇 |
污染及防治 | 1238篇 |
评价与监测 | 320篇 |
社会与环境 | 225篇 |
灾害及防治 | 52篇 |
出版年
2023年 | 35篇 |
2022年 | 36篇 |
2021年 | 62篇 |
2020年 | 42篇 |
2019年 | 55篇 |
2018年 | 113篇 |
2017年 | 119篇 |
2016年 | 125篇 |
2015年 | 125篇 |
2014年 | 144篇 |
2013年 | 367篇 |
2012年 | 227篇 |
2011年 | 307篇 |
2010年 | 222篇 |
2009年 | 250篇 |
2008年 | 265篇 |
2007年 | 312篇 |
2006年 | 286篇 |
2005年 | 219篇 |
2004年 | 177篇 |
2003年 | 166篇 |
2002年 | 191篇 |
2001年 | 98篇 |
2000年 | 85篇 |
1999年 | 66篇 |
1998年 | 68篇 |
1997年 | 79篇 |
1996年 | 61篇 |
1995年 | 75篇 |
1994年 | 71篇 |
1993年 | 42篇 |
1992年 | 47篇 |
1991年 | 37篇 |
1990年 | 34篇 |
1989年 | 22篇 |
1988年 | 31篇 |
1987年 | 26篇 |
1986年 | 34篇 |
1985年 | 22篇 |
1984年 | 27篇 |
1983年 | 31篇 |
1982年 | 28篇 |
1981年 | 25篇 |
1980年 | 25篇 |
1979年 | 30篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1974年 | 13篇 |
1965年 | 14篇 |
1957年 | 13篇 |
排序方式: 共有5174条查询结果,搜索用时 15 毫秒
101.
The machair sand dune systems of the Outer Hebrides of Scotland are a unique habitat, which is rare within both a global and
European context. Unusually, the machair habitat also represents an agricultural resource that is very important to the Hebridean
people, having been subject to both grazing and cultivation throughout the historical period. Following designation as an
Environmentally Sensitive Area (ESA) in 1988, the machairs of South Uist have been studied with the aim of understanding the
links between agricultural practice and their plant community and ecosystem dynamics. This research focused primarily on the
effects of cultivation practices and their role in maintaining plant species richness and community and ecosystem stability.
Within two carefully selected areas, the successional plant communities of machair at different stages of recovery following
ploughing and cultivation of cereals and potato patches or ‘lazy beds’ were identified at both a macro- and micro-level. Investigations
of the vegetation recovery processes on turves taken from newly ploughed land indicated that the initial stages of recolonization
are characterized primarily by rapid vegetative reproduction and growth, although re-vegetation by seeds is also an important
factor. The implications of these findings for the long-term management of machair plant communities are discussed and in
particular the need to maintain old cultivation practices such as shallow ploughing. The need for more detailed research into
both seed banks and seed rain and into processes of vegetative reproduction is stressed.
Nomenclature: Clapham et al. (1981) and Stace (1991, 1997) for vascular plants; Hubbard (1984) for grasses; Pankhurst & Mullin (1991) for
the regional flora; Dobson (1992) for lichens; Watson (1981) for mosses and liverworts. 相似文献
102.
103.
104.
Lucas Ferrante Augusto Getirana Fabricio Beggiato Baccaro Jochen Schöngart Ana Cristina Monteiro Leonel Renato Gaiga Michel Varajão Garey Philip Martin Fearnside 《Conservation biology》2023,37(3):e14033
Given the speed at which humans are changing the climate, species with high degrees of endemism may not have time to avoid extinction through adaptation. We investigated through teleconnection analysis the origin of rainfall that determines the phylogenetic diversity of rainforest frogs and the effects of microclimate differences in shaping the morphological traits of isolated populations (which contribute to greater phylogenetic diversity and speciation). We also investigated through teleconnection analysis how deforestation in Amazonia can affect ecosystem services that are fundamental to maintaining the climate of the Atlantic rainforest biodiversity hotspot. Seasonal winds known as flying rivers carry water vapor from Amazonia to the Atlantic Forest, and the breaking of this ecosystem service could lead Atlantic Forest species to population decline and extinction in the short term. Our results suggest that the selection of morphological traits that shape Atlantic Forest frog diversity and their population dynamics are influenced by the Amazonian flying rivers. Our results also suggest that the increases of temperature anomalies in the Atlantic Ocean due to global warming and in the Amazon forest due to deforestation are already breaking this cycle and threaten the biodiversity of the Atlantic Forest hotspot. 相似文献
105.
Frequency and timing of extrapair fertilisation in the polyandrous red phalarope (Phalaropus fulicarius) 总被引:1,自引:0,他引:1
James Dale Robert Montgomerie Denise Michaud Peter Boag 《Behavioral ecology and sociobiology》1999,46(1):50-56
In sequentially polyandrous bird species, where females mate with different males in succession during a single breeding
season, sperm stored by females can occasionally lead to extrapair fertilisations (EPFs) in clutches cared for by the second
and subsequent males. Thus, we predicted that in red phalaropes (Phalaropus fulicarius) – a sex-role-reversed, sequentially polyandrous, arctic breeding shorebird – EPFs would occur more frequently in clutches
laid later in the breeding season. We used multilocus DNA profiling to examine the frequency and timing of EPFs in a population
of red phalaropes breeding in the Canadian high arctic. Using a technique to determine parentage without maternal DNA, we
inferred that 6 of 70 chicks in 18 broods resulted from EPFs – one extrapair chick in each of 6 broods. These results were
supported by a further analysis using microsatellite DNA. As predicted, broods containing EPFs hatched from clutches laid
significantly later in the season than did broods containing no EPFs. The difference in median hatch dates between broods
with and without EPFs was 9.0 days, or 38% of the entire egg-laying period in that season. For the whole breeding season,
we estimated that 6.5% of chicks were sired by extrapair males, which is similar to extrapair paternity estimates for other
sex-role-reversed birds, but relatively low compared to the majority of socially monogamous species studied so far.
Received: 24 August 1998 / Received in revised form: 18 January 1999 / Accepted: 24 January 1999 相似文献
106.
Flat lizards (Platysaurus broadleyi) at Augrabies Falls National Park, South Africa, are restricted to rocky terrain where the predominant tree is the Namaqua
fig (Ficus cordata cordata). P. broadleyi readily feeds on Namaqua figs when they are available, and the lizards sometimes form large (maximum recorded=134) congregations
under fruiting fig trees. The distance lizards travel to fruiting trees also exceed normal daily foraging distances. Location
of fruiting fig trees by a lizard can have a high pay-off because figs are energetically rich and trees fruit irregularly
and asynchronously, resulting in a resource that is available, but unpredictable in time and space. The prediction that bird
activity in fig trees provides a cue to the presence of ripe figs was tested experimentally. By placing cages containing birds
and empty control cages in trees devoid of fruit, we demonstrated that P. broadleyi are drawn to fig trees with high bird congregations. We also tested if the presence of a fig tree was necessary to draw lizards
to bird congregations by placing cages containing birds and empty control cages in a matched-pairs design on rock away from
trees. Namaqua fig trees were not necessary to draw lizards to bird congregations.
Received: 12 May 1998 / Accepted after revision: 30 November 1998 相似文献
107.
Kevin R. Foster Perttu Seppä Francis L. W. Ratnieks Peter A. Thorén 《Behavioral ecology and sociobiology》1999,46(4):252-257
Queen mating frequency was studied in the European hornet, Vespa crabro, by analyzing four DNA microsatellite loci in 20 workers from each of 14 nests. Queens were found to be predominantly singly
mated (9/14), although double (4/14) and triple mating (1/14) also occurred. For most multiply mated queens, paternity was
significantly biased with the majority male fathering on average 80% of the female offspring. The population-wide effective
mating frequency was therefore low (1.11), and sister-sister relatedness high (0.701 ± 0.023 SE). Low effective mating frequency
in Vespa, in combination with data from other vespines, suggests that high paternity frequency is derived in the group. Some problems
with the non-detection of fathers, where the queen was not sampled or shared alleles with males, are analyzed.
Received: 16 November 1998 / Received in revised form: 29 March 1999 / Accepted: 12 April 1999 相似文献
108.
Understanding within-stand variation in diversity of epiphytes will provide an improved basis for producing timber while conserving biological diversity. Two 80-ha, 50–year–old managed stands of conifers were surveyed to locate 0.4 ha putative "diversity" plots, the areas appearing most diverse in lichen epiphytes. These plots were generally located in areas made heterogeneous by canopy gaps, wolf trees (trees with large-diameter lower branches), and old-growth remnant trees. "Matrix" plots, in contrast, were chosen at random from the remaining, more homogenous forest. Diversity plots hosted from 25% to 40% more epiphytic lichen species than matrix plots in both stands. The strongest within-stand gradients in species composition were correlated with percentage of plot occupied by gaps and wolf trees. Percentage of the plot in gaps was correlated with species richness (r = 0.79). In the more structurally diverse stand, diversity and abundance of nitrogen-fixing "cyanolichens" were correlated with percentage of the plot occupied by gaps (0.5 < r < 0.9), and alectorioid lichens were correlated with percentage of the plot occupied by old-growth remnant trees (0.5 < r < 0.6). In the stand with more homogenous structure, percentage of the plot under gaps was correlated with regionally common species that were otherwise absent or sparse in the matrix. Protecting gaps, hardwoods, wolf trees, and old-growth remnant trees during thinning or other partial cutting is likely to promote the majority of epiphytic macrolichens in young conifer forests. Because these features are easily recognized on aerial photos and on the ground by land managers, it is practical to manage for forest structures that would promote lichen diversity. 相似文献
109.
110.