全文获取类型
收费全文 | 6737篇 |
免费 | 59篇 |
国内免费 | 36篇 |
专业分类
安全科学 | 100篇 |
废物处理 | 432篇 |
环保管理 | 471篇 |
综合类 | 932篇 |
基础理论 | 1446篇 |
环境理论 | 10篇 |
污染及防治 | 2367篇 |
评价与监测 | 630篇 |
社会与环境 | 426篇 |
灾害及防治 | 18篇 |
出版年
2023年 | 78篇 |
2022年 | 195篇 |
2021年 | 249篇 |
2020年 | 101篇 |
2019年 | 91篇 |
2018年 | 235篇 |
2017年 | 222篇 |
2016年 | 345篇 |
2015年 | 192篇 |
2014年 | 373篇 |
2013年 | 630篇 |
2012年 | 424篇 |
2011年 | 443篇 |
2010年 | 334篇 |
2009年 | 267篇 |
2008年 | 386篇 |
2007年 | 411篇 |
2006年 | 336篇 |
2005年 | 244篇 |
2004年 | 190篇 |
2003年 | 167篇 |
2002年 | 159篇 |
2001年 | 94篇 |
2000年 | 73篇 |
1999年 | 53篇 |
1998年 | 27篇 |
1997年 | 23篇 |
1996年 | 18篇 |
1995年 | 41篇 |
1994年 | 27篇 |
1993年 | 16篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1987年 | 9篇 |
1985年 | 8篇 |
1967年 | 9篇 |
1966年 | 13篇 |
1965年 | 16篇 |
1964年 | 31篇 |
1963年 | 12篇 |
1962年 | 17篇 |
1961年 | 12篇 |
1960年 | 9篇 |
1959年 | 27篇 |
1958年 | 37篇 |
1957年 | 20篇 |
1956年 | 14篇 |
1955年 | 19篇 |
排序方式: 共有6832条查询结果,搜索用时 312 毫秒
961.
Jesús Martínez-Padilla 《Behavioral ecology and sociobiology》2006,60(4):510-515
Theoretical models of parental care predict differential allocation in relation to the expected fitness of the offspring. As birds must allocate all the resources required for embryonic development in self-contained packages, maternal egg allocation takes a central role in avian life histories. It is predicted that mothers can influence offspring performance by varying the size or composition of their eggs. In this context, T cell-mediated immune response has been revealed as a valuable tool to evaluate fledgling fitness. However, little is known about its relationships to egg mass. I describe a negative association between egg mass and cellular immune response in Eurasian kestrel nestlings (Falco tinnunculus) throughout 3 years. To explore how environmental conditions could mediate this relationship, I experimentally supplied food to females before egg formation in the third study year. I found that this relationship turned to positive in food-supplied females without any effect on egg size. This result shows that environmental conditions before egg formation mediate the relationship between egg mass and future immune response of the nestlings. I suggest that females may be constrained in improving the future immune response of their offspring due to resource allocation trade-offs determined by their pre-laying condition. 相似文献
962.
Identifying reproductive stocks in commercial species is relevant to fishery management strategies. We obtained muscle samples
of California spiny lobster (Panulirus interruptus) from six localities along the west coast of the Baja California Peninsula and analyzed the genetic structure using mtDNA
RFLPs. Our results indicated that all localities shared the same major haplotypes and showed a spatial homogeneity in the
distribution of haplotype frequencies. An analysis of molecular variance indicated that only 0.84% of the genetic variability
was explained by differences among localities and was not significantly different from zero. Weak divergences were found between
Bahía Magdalena, the most southerly locality, in relation to other populations. Major oceanographic processes along this coast,
combined with a long larval period that supports passive transport among localities, are suggested to explain the results. 相似文献
963.
Summary. Geographic variations in the correspondence between diaspore phenotypes and disperser behavior are thought to determine the
evolution of plant-animal dispersal mutualisms. Helleborus foetidus is a widely distributed plant in Western Europe, which seeds bear a lipid rich elaiosome attracting ant dispersers. Laboratory
cross-tests were conducted to check the correspondence between diaspore phenotypes and ant preference in two localities of
the Iberian Peninsula, Caurel and Cazorla, separated by 750 km. Diaspores from Caurel were systematically preferred to those
from Cazorla by Formica lugubris (the major disperser at Caurel), and Aphaenogatser iberica and Camponotus cruentatus (both major dispersers at Cazorla). Further bioassays conducted on A. iberica only showed that differences in elaiosome traits were sufficient to explain ant preference. Separation of the lipid fractions
composing the elaiosome revealed that triglycerides, diglycerides and free fatty acids were all dominated by oleic acid. The
elaiosomes from Caurel contained relatively more free oleic acid but were less concentrated in linoleyl-containing triglycerides,
free palmitic acid and free linoleic acid than those from Cazorla. The three lipid fractions were attractive to ants but dummies
soaked with the free fatty acids extracted from Caurel were preferred to those from Cazorla. Taken together, these results
reinforce the idea that oleic acid is a major releaser of seed collection by ants and suggest that geographic variations in
free fatty acid composition affect the probability of diaspore removal by ants which in turn potentially determine plant demography. 相似文献
964.
The structure of megabenthic decapod crustacean assemblages on the Galician (north-west Spain) continental shelf (100 to
200 depth) and upper slope (200 to 500 m) was analyzed based on surveys carried out in autumn and spring, from 1980 to 1987.
Forty species belonging to 19 families were caught. The portunid crab Polybius henslowii, a species with pelagic phases, was the most abundant species, but displayed strong spatial and temporal fluctuations. Other
dominant species were the Norway lobster Nephrops norvegicus, the portunid Liocarcinus depurator, the galatheids Munida intermedia and M. sarsi, and the shrimps Solenocera membranacea, Plesionika heterocarpus, Pasiphaea sivado and Dichelopandalus bonnieri. Total abundance and biomass (average values excluding Polybius henslowii = 255 individuals and 2.06 kg/30 min tow) and species richness and diversity, H′ (6.85 species and H′ = 1.45 per tow) displayed a significant positive correlation with depth, and strong interannual fluctuations. The factors
determining community organization were depth and, to a lesser extent, spatial structure. There was clear evidence of bathymetric
zonation, differentiating between species characteristic of the slope (D. bonnieri and Pasiphaea sivado), shelf-slope edge (Macropipus tuberculatus, Pontophilus spinosus, Munida sarsi, S. membranacea, Processa spp.) and shelf (L. depurator, Macropodia tenuirostris, Paguridae and Chlorotocus crassicornis). The spatial zonation was related to changes in oceanography and sediment along the continental margin. Goneplax rhomboides, N. norvegicus, C. crassicornis and Alpheus glaber are benthic species which generally exhibit burrowing behaviour, and they were found mainly in the southern area where there
are fine sediments due to the outwelling from the Rías Baixas. Different benthopelagic shrimps (Pontophilus spinosus, Plesionika heterocarpus,Processa spp. and Pasiphaea sivado) were typical of the zone just north of Fisterra, characterized by a convergence of water masses bringing about an increase
in productivity due to upwelling. The benthic anomuran and brachyuran crabs Munida intermedia, M.␣sarsi, L.␣depurator and Macropipus tuberculatus were characteristic of the northwestern zone between Fisterra and Estaca, where the infauna reaches high biomass despite
coarser sediments with a lower concentration of organic material than in the southern area. Lastly, both the Paguridae and
Macropodia tenuirostris were species typically found in the waters in the northern shelf. Based on interannual changes in assemblage structure, two
periods could be distinguished: between 1980 and 1984, when Polybius henslowii, D. bonnieri and Pasiphaea sivado had abundance peaks; and another period from 1985 to 1987 when L. depurator, Munida intermedia, M.␣sarsi and Macropipus tuberculatus increased in abundance.
Received: 21 May 1996 / Accepted: 9 August 1996 相似文献
965.
In the asperillo dune system, Southwest Spain, lichen vegetation covering the dune sand, has a low species diversity but is
an important component of the perennial vegetation, providing stability, nutrients, and moisture to the soil layer. The Asperillo
dunes harbour (1) natural ecosystems, (2) disturbed systems affected by forestry activities where the natural vegetation is
eliminated, and (3) pine forest resulting from afforestation withPinus pinea since the end of the 1940s where the composition and abundance of the lichen flora has been drastically changed.
Our hypothesis was that the lichen species composition and distribution are influenced by the type and period of human intervention.
To test this hypothesis a 1.2 km × 1.1 km area, which includes zones with different degrees of conservation and perturbation,
consisting of five different habitats, was selected: well preservedJuniperus woodland,Pinus pinea plantations with dense scrub, dense scrub,P. pinea plantations cleared from scrub, and pioneer scrub in recent pine afforestation. In each area, randomly located 5m × 5 m homogeneous
plots were sampled. In each plot the cover of shrub and lichen species was recorded.
The first results show that lichen cover is higher in the most preserved areas,Cladonia mediterranea being the dominant species under theJuniperus phoenicea canopy. The lichen community changes in composition and abundance depending on the time elapsed since the last perturbation. 相似文献
966.
Malia Chevolot Peter H. J. Wolfs Jónbjörn Pálsson Adriaan D. Rijnsdorp Wytze T. Stam Jeanine L. Olsen 《Marine Biology》2007,151(4):1275-1286
Population genetic structure of the thorny skate (Amblyraja radiata) was surveyed in >300 individuals sampled from Newfoundland, Iceland, Norway, the Kattegat and the central North Sea. A 290-bp
fragment of the mt cytochrome-b gene was first screened by SSCP. Sequences of SSCP haplotypes revealed 34 haplotypes, 14 of
which were unique to Iceland, 3 to Newfoundland, 1 to Norway and 3 to the Kattegat. The global F
ST was weak but significant. Removal of the two Kattegat locations, which were the most differentiated, resulted in no significant
genetic differentiation. Haplotype diversity was high and evenly distributed across the entire Atlantic (h = 0.8) with the exception of the North Sea (h = 0.48). Statistical parsimony revealed a star-like genealogy with a central widespread haplotype. A subsequent nested clade
analysis led to the inference of contiguous expansion with evidence for long distance dispersal between Newfoundland and Iceland.
Historical demographic analysis showed that thorny skates have undergone exponential population expansion that started between
1.1 million and 690,000 years ago; and that the Last Glacial Maximum apparently had little effect. These results strongly
differ from those of a parallel study of the thornback ray (Raja clavata) in which clear structure and former refugial areas could be identified. Although both species have similar life history
traits and overlapping ranges, the continental shelf edge apparently does not present a barrier to migration in A. radiata, as it does for R. clavata. 相似文献
967.
968.
F. Mougeot J. Martínez-Padilla L. Pérez-Rodríguez G. R. Bortolotti 《Behavioral ecology and sociobiology》2007,61(5):741-751
Among the most familiar sexual signals are red, yellow, and orange sexual traits pigmented by carotenoids. Many birds can
detect near-ultraviolet (UV) light, and UV signals can play key roles in mate choice. Grouse (Tetraonidae) exhibit bright
carotenoid-dependent sexual ornaments, their supra-orbital combs, which to humans appear orange-red. Combs also reflect in
the UV, which is not visible to humans but is likely to be visible to grouse. In male red grouse Lagopus lagopus scoticus, we show that comb UV reflectance decreases with increasing comb size and redness. By removing the epidermis of combs, where
carotenoid pigments are, we show that the UV reflectance is a property of the dermis, underneath the red pigmented epidermis.
Carotenoid pigmentation of combs acted as a mask to reduce reflectance by the dermis in the range 400–550 nm and in the UV,
300–400 nm. Patagium skin (non-ornamental skin under the wing) also reflects in the UV, but epidermis removal on this bare
part tended to reduce UV reflectance, whereas removal of the red epidermis of combs increased UV reflectance. Males in better
condition (greater body mass relative to size) had bigger and redder combs, but with less UV. Thus, carotenoid pigments of
grouse combs are deposited on a white background with significant UV reflectance, which can influence how the signal is perceived
by conspecifics. Carotenoid-based traits exhibit UV reflectance in a number of species, but how UV reflectance and carotenoid
pigmentation influence colour remains little known for integumentary ornaments compared to plumage traits. UV vision is not
uncommon in birds and other animals, so future studies should investigate how UV reflectance influences the perception of
carotenoid-based signals of quality. 相似文献
969.
When searching for flying insects, Molossops temminckii uses unusual echolocation calls characterized by upward modulation of frequency vs time (UFM). Call frequency increases asymptotically
in the relatively long (∼8 ms) pulses from a starting frequency of ∼40 kHz to a long narrowband tail at ∼50 kHz. When approaching
a prey, the bat progressively increases the duration of calls and intersperses in the sequence broadband downwardly frequency-modulated
signals with a terminal frequency of about 53 kHz, which totally replaces the UFM signals at the end of the approach phase.
The sequence progresses to a capture buzz resembling those from other molossid and vespertilionid bats. The M. temminckii wing morphology is characterized by an average aspect ratio and a high wing loading, suggesting that it is more maneuverable
than the typical Molossidae but less than typical Vespertilionidae. M. temminckii regularly forages near clutter, where it needs to pay attention to the background and might face forward and backward masking
of signals. We hypothesize that the UFM echolocation signals of M. temminckii represent an adaptation to foraging near background clutter in a not very maneuverable bat needing a broad attention window.
The broadband component of the signal might serve for the perception of the background and the narrowband tail for detection
and perhaps classification of prey. Bats may solve the signal masking problems by separating emission and echoes in the frequency
domain. The echolocation behavior of M. temminckii may shed light on the evolution of the narrowband frequency analysis echolocation systems adopted by some bats foraging within
clutter. 相似文献
970.
Carmen?Rossini Alexander?Bezzerides Andrés?González Maria?Eisner Thomas?EisnerEmail author 《Chemoecology》2003,13(4):199-205
Summary. Evidence is presented that pyrrolizidine alkaloid acquired
by Utetheisa ornatrix (Lepidoptera, Arctiidae) as a larva
from Crotalaria foodplants is incorporated in part into the scales
of the adult. A single forewing of a male or female moth may contain in
the order of 6 to 13 g monocrotaline in its scale cover or about 1 to 2%
of the moths systemic monocrotaline content. Based on estimates of the number
of scales per forewing, the monocrotaline content of individual scales is calculated
to be in the order of 0.1 and 0.2 ng monocrotaline per male and female scale,
respectively. This amounts to concentrations of about 1 and 3%, values roughly at
a par with the average systemic concentration (0.5-0.6%) previously determined
for monocrotaline in Utetheisa. It is argued that the presence of pyrrolizidine alkaloid
in the moths scale coating could account for the promptness with which adult Utetheisa are
rejected by spiders. It is suggested further that chemical impregnation of scales with substances
deterrent to predators may be more widespread among insects than generally assumed. 相似文献