全文获取类型
收费全文 | 15334篇 |
免费 | 175篇 |
国内免费 | 131篇 |
专业分类
安全科学 | 533篇 |
废物处理 | 620篇 |
环保管理 | 2362篇 |
综合类 | 2505篇 |
基础理论 | 3979篇 |
环境理论 | 19篇 |
污染及防治 | 3784篇 |
评价与监测 | 977篇 |
社会与环境 | 749篇 |
灾害及防治 | 112篇 |
出版年
2023年 | 88篇 |
2022年 | 148篇 |
2021年 | 136篇 |
2020年 | 112篇 |
2019年 | 143篇 |
2018年 | 254篇 |
2017年 | 238篇 |
2016年 | 344篇 |
2015年 | 278篇 |
2014年 | 376篇 |
2013年 | 1186篇 |
2012年 | 519篇 |
2011年 | 726篇 |
2010年 | 565篇 |
2009年 | 627篇 |
2008年 | 708篇 |
2007年 | 728篇 |
2006年 | 633篇 |
2005年 | 541篇 |
2004年 | 469篇 |
2003年 | 490篇 |
2002年 | 441篇 |
2001年 | 541篇 |
2000年 | 395篇 |
1999年 | 262篇 |
1998年 | 174篇 |
1997年 | 202篇 |
1996年 | 207篇 |
1995年 | 233篇 |
1994年 | 233篇 |
1993年 | 194篇 |
1992年 | 170篇 |
1991年 | 191篇 |
1990年 | 194篇 |
1989年 | 175篇 |
1988年 | 126篇 |
1987年 | 134篇 |
1986年 | 141篇 |
1985年 | 106篇 |
1984年 | 129篇 |
1983年 | 137篇 |
1982年 | 146篇 |
1981年 | 134篇 |
1980年 | 111篇 |
1979年 | 126篇 |
1978年 | 78篇 |
1977年 | 84篇 |
1976年 | 72篇 |
1975年 | 85篇 |
1973年 | 73篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
22.
Certain hydrothermal vent invertebrates, e.g. Riftia pachyptila and Calyptogena magnifica, are clearly established as harboring dense populations of chemoautotrophic sulfur bacteria in specialized tissues. By contrast, the physiological characteristics of the abundant intracellular gill symbiont of the vent mussel Bathymodiolus thermophilus have been questioned. The low activities of enzymes diagnostic for CO2 fixation (Calvin cycle) and for sulfur-driven energy generation, as measured by other investigators, have been attributed to bacterial contamination of the gill surface. Based on research at the Galápagos Rift hydrothermal vents in 1988 and subsequent laboratory experiments, the current study confirms that the B. thermophilus symbiont is a psychrophile for which thiosulfate and sulfide stimulate CO2 fixation. It strongly indicates that the symbiont is a chemoautotroph by establishing the following: (1) Sulfide and thiosulfate can stimulate CO2 fixation by partially purified symbionts by up to 43-fold and 120-fold, respectively; (2) the ribulose-1,5-bisphosphate carboxylase/oxygenase activity of the symbiont is sufficient to account for its sulfide- or thiosulfate-stimulated CO2 incorporation; (3) the symbiont's molar growth yield on thiosulfate, as judged by CO2 incorporation, is indistinguishable from that of free-living chemoautotrophs. Due to the high protein-degrading activity of B. thermophilus gill lysate, it is also suggested that host lysis of symbionts plays a more important role in the nutrition of the vent mussel than in R. pachyptila or C. magnifica, for which no comparable protein-degrading activity was found. 相似文献
23.
24.
25.
From 1988 to 1991, we studied the postfledging dispersal of 31 radio-tagged White-crowned Pigeons ( Columba leucocephala ) from three natal keys in Florida Bay. Immature birds dispersed from the natal keys at 26–45 days after batching, and most young dispersed more than 20 km during the first 10 days postdispersal. Dispersing birds flew either north to the Florida mainland or east to northeast to the mainline Florida Keys. On the mainland, immature birds fed nearly exclusively within Everglades National Park or an adjacent state wildlife management area. On the mainline keys, White-crowned Pigeons selectively used 5.01–20 ha forest fragments (p < 0.10) during the first 72 hours postdispersal. After this period, dispersing birds showed no preference among fragment size classes but used deciduous seasonal forests more frequently than suburban habitat(p < 0.10). The spatial pattern of dispersal on the mainline keys suggests that, during the first 72 hours postdispersal. White-crowned Pigeons are not able to reach northern Key Largo, where 69% of the deciduous seasonal forests are protected in state or federal ownership. Protection of large forest fragments, especially on southern Key Largo, should be a priority for maintaining populations of White-crowned Pigeons. These forests provide a series of "stepping stones" that enable dispersing immature White-crowned Pigeons to fly to more distant areas where habitat availability is less restricted. This species is threatened in Florida and may play an important role in maintaining plant species diversity in the seasonal deciduous forests of south Florida by dispersing seeds of at least 37 species of trees and shrubs. Protection of sufficient habitat to allow successful postfledging dispersal of this important seed disperser will also protect the ecosystem's biodiversity. 相似文献
26.
The brittle stars Amphiura filiformis (Müller) and Ophiura albida (Forbes) were exposed to different oxygen saturations (100, 10, 5, 3, and <1% oxygen saturation) and to physiological anoxia
(<1% oxygen saturation) at different total sulfide concentrations (0, 2, 20, 200 μM). The mortality was followed during experiments and the median survival time (LT50) was determined. The infaunal A. filiformis had a significantly higher tolerance to both hypoxia and sulfide than did the epibenthic O. albida. After exposure to 10% oxygen saturation for a month, only 2.0% A. filiformis and 0% O. albida were dead. In oxygen saturations <1% A. filiformis and O. albida had a LT50 of 7.5 and 2.5 d, respectively. The presence of even very small concentrations of sulfide decreased the survival significantly.
Sulfide is shown to be the key factor for the survival of the two species.
Received: 11 October 1996 / Accepted: 12 November 1996 相似文献
27.
Because the classification of extant and fossil articulate brachiopods is based largely upon shell characters observable in fossils, it identifies morphotaxa whose biological status can, in practice, best be inferred from estimates of genetic divergence. Allozyme polymorphism and restriction fragment length polymorphism of mitochondrial DNA (mtDNA RFLP) have been used to show that nuclear and mitochondrial genetic divergence between samples of the cancellothyridid brachiopods Terebratulina septentrionalis from Canada and T. retusa from Europe is compatible with biological speciation, but the genetic distances obtained were biased by methodological limitations. Here, we report estimates of divergence in 12S rDNA mitochondrial sequences within and between samples of these brachiopods. The sequence-based genetic distance between these samples (5.98ǂ.07% SE) is at least 10 times greater than within them and, since they also differ in a complex life-history trait, their species status is considered to be securely established. Divergence levels between 12S rDNA genes of three other cancellothyridids, T. unguicula from Alaska, T. crossei from near Japan, and Cancellothyris hedleyi from near Australia are higher than between the two North Atlantic species, and the mean nucleotide distance between all these cancellothyrids is similar to the mean distance between species of Littorina (Mollusca: Gastropoda). Sequences of both 12S and 16S genes from cancellothyridids and other short-looped brachiopod species show neither saturation nor lineage-specific rate differences and, when analysed with different outgroups, either separately or together, yield one unexpected, but well-supported, tree with Alaskan T. unguicula basal and C. hedleyi nested within Terebratulina, i.e. these genera are paraphyletic. A geologically dated divergence between Antarctic and New Zealand species of the short-looped brachiopod Liothyrella is used to calibrate the rate of 12S divergence at ca. 0.1% per million years (MY), and this rate is used to infer that T. septentrionalis and T. retusa have been diverging for ca. 60 MY and that they and T. unguicula have been diverging from their last common ancestor for ca. 100 MY. This indicates a Mesozoic origin for the present-day distribution of cancellothyridids and the basal position of T. unguicula suggests a possible North Pacific centre of origin, with separate Atlantic and Pacific radiations. The inclusion of Cancellothyris within Terebratulina also shows that adult shell characters such as umbo, foramen and symphytium shape, whilst probably indispensible for the practical classification of fossils, are not reliable guides to genealogy. 相似文献
28.
M Mora R Skiles B McKinney M Paredes D Buckler D Papoulias D Klein 《Environmental pollution (Barking, Essex : 1987)》2002,116(1):169-176
Peregrine falcons (Falco peregrinus) have been recorded nesting in Big Bend National Park, Texas, USA and other areas of the Chihuahuan Desert since the early 1900s. From 1993 to 1996, peregrine falcon productivity rates were very low and coincided with periods of low rainfall. However, low productivity also was suspected to be caused by environmental contaminants. To evaluate potential impacts of contaminants on peregrine falcon populations, likely avian and bat prey species were collected during 1994 and 1997 breeding seasons in selected regions of western Texas, primarily in Big Bend National Park. Tissues of three peregrine falcons found injured or dead and feathers of one live fledgling also were analyzed. Overall, mean concentrations of DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene], a metabolite of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane], were low in all prey species except for northern rough-winged swallows (Stelgidopteryx serripennis, mean = 5.1 microg/g ww). Concentrations of mercury and selenium were elevated in some species, up to 2.5 microg/g dw, and 15 microg/g dw, respectively, which upon consumption could seriously affect reproduction of top predators. DDE levels near 5 microg/g ww were detected in carcass of one peregrine falcon found dead but the cause of death was unknown. Mercury, selenium, and DDE to some extent, may be contributing to low reproductive rates of peregrine falcons in the Big Bend region. 相似文献
29.
V. Thomas Parker 《Conservation biology》2002,16(5):1444-1446
30.
Jürgen Heinze Bernhard Stengl Matthew F. Sledge 《Behavioral ecology and sociobiology》2002,52(1):59-65
Workers in de-queened colonies of the neotropical ant, Pachycondyla cf. inversa, form linear or near-linear dominance hierarchies by violent antennation and biting. In these rank orders, social status and ovarian activity are on average highly correlated. Whereas the presence of a fertile queen appears to be sufficient to prevent workers from laying eggs, fertile workers do not completely control reproduction by their nestmates, suggesting that workers are able to differentiate between an egg-laying queen and an egg-laying worker. Here we show that the composition of cuticular hydrocarbons of egg-laying workers is quantitatively and qualitatively different from that of non-laying workers and resembles the hydrocarbon blend of the queen but does not completely match it. Furthermore, using discriminant analysis, it was possible to distinguish workers with four different classes of ovarian development based only on their cuticular hydrocarbon profiles. Fertility-associated changes in cuticular hydrocarbons may play an important role in the behavioural regulation of reproduction in this ant. 相似文献