全文获取类型
收费全文 | 815篇 |
免费 | 6篇 |
国内免费 | 6篇 |
专业分类
安全科学 | 12篇 |
废物处理 | 62篇 |
环保管理 | 68篇 |
综合类 | 88篇 |
基础理论 | 134篇 |
污染及防治 | 294篇 |
评价与监测 | 95篇 |
社会与环境 | 74篇 |
出版年
2023年 | 15篇 |
2022年 | 50篇 |
2021年 | 63篇 |
2020年 | 24篇 |
2019年 | 23篇 |
2018年 | 41篇 |
2017年 | 35篇 |
2016年 | 56篇 |
2015年 | 21篇 |
2014年 | 40篇 |
2013年 | 76篇 |
2012年 | 34篇 |
2011年 | 58篇 |
2010年 | 33篇 |
2009年 | 35篇 |
2008年 | 36篇 |
2007年 | 29篇 |
2006年 | 40篇 |
2005年 | 25篇 |
2004年 | 22篇 |
2003年 | 13篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1970年 | 1篇 |
1968年 | 2篇 |
1957年 | 1篇 |
1938年 | 1篇 |
排序方式: 共有827条查询结果,搜索用时 578 毫秒
321.
Marco Antonio DS Guidugli-Lazzarini KR do Nascimento AM Simões ZL Hartfelder K 《Die Naturwissenschaften》2008,95(10):953-961
The switch from within-hive activities to foraging behavior is a major transition in the life cycle of a honeybee (Apis mellifera) worker. A prominent regulatory role in this switch has long been attributed to juvenile hormone (JH), but recent evidence
also points to the yolk precursor protein vitellogenin as a major player in behavioral development. In the present study,
we injected vitellogenin double-stranded RNA (dsVg) into newly emerged worker bees of Africanized genetic origin and introduced them together with
controls into observation hives to record flight behavior. RNA interference-mediated silencing of vitellogenin gene function shifted the onset of long-duration flights (>10 min) to earlier in life (by 3–4 days) when compared with sham
and untreated control bees. In fact, dsVg bees were observed conducting such flights extremely precociously, when only 3 days
old. Short-duration flights (<10 min), which bees usually perform for orientation and cleaning, were not affected. Additionally,
we found that the JH titer in dsVg bees collected after 7 days was not significantly different from the controls. The finding
that depletion of the vitellogenin titer can drive young bees to become extremely precocious foragers could imply that vitellogenin
is the primary switch signal. At this young age, downregulation of vitellogenin gene activity apparently had little effect on the JH titer. As this unexpected finding stands in contrast with previous results
on the vitellogenin/JH interaction at a later age, when bees normally become foragers, we propose a three-step sequence in
the constellation of physiological parameters underlying behavioral development.
David Santos Marco Antonio and Karina Rosa Guidugli-Lazzarini contributed equally to the present study. 相似文献
322.
Santos FJ López-Gutiérrez JM García-León M Suter M Synal HA 《Journal of environmental radioactivity》2005,84(1):103-109
In this work we present results of the (129)I/(127)I ratio in aerosols of Seville, Southwest of Spain (37.4 degrees N,6 degrees W). A radiochemical method is applied to extract the iodine from the aerosols and prepare samples to be measured by accelerator mass spectrometry (AMS) at the ETH facility in Zürich. We have found the possibility of monitoring the (129)I/(127)I isotopic ratio on a two-days basis with sensitivities in the order of 10(4)-10(5) atoms (129)I/m(3), and values of 10(-8)-10(-9) for the isotopic ratio. 相似文献
323.
324.
Baraka Kuguru Gidon Winters Sven Beer Scott R. Santos Nanette E. Chadwick 《Marine Biology》2007,151(4):1287-1298
Corallimorpharians may dominate some habitats on coral reefs and compete with stony corals for access to light, yet little
is known concerning their photosynthetic traits. At Eilat in the northern Red Sea, we observed that the abundance of individuals
of the corallimorpharian Rhodactis rhodostoma decreased significantly with depth on the reef slope. Field and laboratory experiments revealed that they employ several
mechanisms of photoadaptation to high irradiance on the shallow reef flat. Their endosymbiotic microalgae (zooxanthellae)
varied significantly in both abundance and chlorophyll content with level of irradiance. Use of a diving pulse amplitude modulated
fluorometer revealed that the zooxanthellae of R. rhodostoma effectively disperse excess light energy by expressing significantly higher values of non-photochemical quenching and maximum
excitation pressure on photosystem II when experimentally exposed to high light (HL) versus low light (LL). Host corallimorpharian
tissues mediated this response by shielding the algal symbionts from high irradiance. The endoderm of host tentacles thickened
significantly and microalgal cells were located further from the mesoglea in HL than in LL. The clades of zooxanthellae hosted
by the corallimorpharians also varied with depth. In shallow water, all sampled individuals hosted clade C zooxanthellae,
while in deep water the majority hosted clade D. The photosynthetic output of individuals of R. rhodostoma was less affected by HL than was that of a stony coral examined. When exposed to both high temperature (HT) and HL, individuals
of R. rhodostoma reduced their maximum quantum yield, but not when exposed to HL at low temperature (LT). In contrast, colonies of the scleractinian
coral Favia favus reduced their photosynthetic output when exposed to HL in both temperature regimes. After 2 weeks of HT stress, R. rhodostoma polyps appeared to bleach completely but re-established their zooxanthella populations upon return to ambient temperature.
We conclude that mechanisms of photoadaptation to high irradiance employed by both the endosymbiotic zooxanthellae and host
corallimorpharians may explain in part the abundance of R. rhodostoma on some shallow reef flats. The ability to survive for weeks at HT while bleached also may allow corallimorpharians to repopulate
shallow reef areas where scleractinians have been killed by thermal stress.
B. Kuguru and G. Winters contributed equally to this work. 相似文献
325.
Anita Aisenberg Carmen Viera Fernando G. Costa 《Behavioral ecology and sociobiology》2007,62(1):29-35
Sexual selection theory predicts that a higher investment in offspring will turn females into the selective sex, while males
will compete for accessing and courting them. However, there are exceptions to the rule. When males present a high reproductive
investment, sex roles can reverse from typical patterns, turning males into the choosy sex, while females locate males and
initiate courtship. In many spiders, males are smaller than females, wandering in search of sedentary females and maximizing
the number of copulations. In the present study, we present findings on the sand-dwelling wolf spider, Allocosa brasiliensis, evidencing a reversal in typical courtship roles reported for the first time in spiders. Males were bigger than females.
Females located males and initiated courtship. Copulation always occurred in male burrows and took place mainly in long burrows.
Males donated their burrows to the females after copulation, closing the entrance before leaving with female cooperation from
inside. Males would provide females with a secure place for ovipositing, being exposed to predation and diminishing their
future mating possibilities until constructing a new burrow. The cost of vacating the burrow and losing the refuge in an unpredictable
habitat, such as sand dunes, would explain the courtship roles reversal in this spider species. Results turn A. brasiliensis as a promising model for discussing the determinants of sex roles and the pressures that drive their evolution and maintenance.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献
326.
Summary Genetic relatedness in social insect colonies may vary spatially or temporally as a result of changes in colony membership due to immigration or to variation in patterns of maternity and paternity. We estimated relatedness for eastern tent caterpillars (Malacosoma americanum) in laboratory colonies derived from egg masses using multilocus genotypic data derived from electrophoresis. This estimate is compared with estimates obtained from colony samples taken in the field at four intervals spanning the larval developmental season. We found that average intracolony relatedness is close to 0.5 initially but declines through the developmental season due to colony merging, showing that caterpillars do not discriminate between siblings and nonsiblings in order to preserve colony family structure. Using the intracolony values together with relatedness values for higher levels of population structure, we estimated the effective mean number of simple families represented in single colonies through the season. The overall effective number of families per tent increased from one at the time of eclosion to 1.3 by the end of the season. Average intracolony relatedness remained relatively high despite the occurrence of colony merging, apparently as a result of the low density of tents on most trees, combined with high relatedness within the original colonies. Thus, high intracolony relatedness is maintained in M. americanum populations through the effects of adult dispersal, mating, and oviposition patterns, rather than through behavioral discrimination mechanisms of the larvae. These findings underscore the importance of considering the causes of temporal variation in genetic relatedness as well as the consequences for the indirect component of inclusive fitness.
Correspondence to: J.T. Costa 相似文献
327.
S. I. C. O. Santos L. De Neve J. T. Lumeij M. I. Förschler 《Behavioral ecology and sociobiology》2007,61(9):1499-1506
The assessment of plumage colouration has become a common procedure in many ornithological studies, especially after the discovery
of differences between avian and human visual systems, namely the avian ability to perceive ultraviolet wavelengths. There
are many techniques available for plumage colour assessment. Nevertheless, unidirectional reflectance spectrometry seems actually
to be the method of choice and is used in most studies. The active avian visual communication skills, the physical characteristics
of the plumage surface and the birds’ body shape prompted us to study plumage colouration with different angles of incidence
and observation by bidirectional reflectance spectrometry. In this study, we explore the effect of different angles of incidence
and observation, on a single plane of incidence, on the reflectance spectrometric assessment of five differently coloured
body regions of the blue fronted Amazon parrot (Amazona aestiva). Measurements were made using a AVS-USB2000 spectrometer with a DH-2000 light source and two different reflection probes
(bifurcated fibre optic probe and a specially designed fibre holder). The results of this study illustrate clear angle dependence
of colour parameters in differently coloured non-iridescent plumage regions of the blue fronted Amazon parrot. Our results
may have direct implications on the observed transmitted information of display and its associated predation risk (trade-off)
in birds, but also in other animals. Moreover, the results show that unidirectional reflectance spectrometry alone may be
a rather limited procedure to quantify and compare true colour of a complex surface such as birds’ plumage. Therefore, slight
but behavioural important characteristics of plumage pattern may remain undiscovered with this method. 相似文献
328.
Ruiz-Pérez M Almeida M Dewi S Costa EM Pantoja MC Puntodewo A de Postigo AA de Andrade AG 《Ambio》2005,34(3):218-223
Extractive reserves constitute an innovative approach to match conservation and development objectives, which were originally envisaged as part of a land struggle by forest dwellers in Brazil. In spite of the idea's popularity and the attempts to apply the concept to different tropical regions, there has been little analysis of the combined conservation and development performance of extractive reserve programs. We present a detailed analysis of deforestation and demographic and socioeconomic changes in Alto Juruá, the first extractive reserve created in Brazil in 1990. Forest cover has remained fairly stable. Population has declined slightly, with some internal displacements. The cash economy base has shifted from the original rubber production to a diversified portfolio of agriculture and livestock, and there has been a dramatic rise in nonagrarian income. We conclude that the Reserve represents a very dynamic setting with positive conservation and development outcomes during its first decade. 相似文献
329.
Etienne Paul Delmira Beatriz Wolff Juan Carlos Ochoa Rejane Helena Ribeiro da Costa 《Water environment research》2007,79(7):765-774
The reduction of organic and nitrogen pollution of wastewater was investigated in two hybrid reactors and compared with the reduction obtained by using a conventional activated sludge reactor (ASR) run as a control. Both HR-1 and HR-2 were activated sludge systems where a low-density carrier, P1 (polyethylene) for HR-1 and P2 (recycled plastics) for HR-2, was added. Firstly, the three reactors were operated at 10 days Suspended Solid Retention Time (SRT(SS)), leading to a complete nitrification. Secondly, the SRT(SS) for each reactor was lowered to 3 days. Nitrification was lost for the ASR but remained complete for HR's. Respirometric techniques were used to measure fixed or suspended biomass activities for heterotrophic and autotrophic biomass. More than 90% of the autotrophic activity was found on the supports whatever the SRT(SS) used. The results may underline the role of the carrier geometry or surface characteristics on the autotrophic/heterotrophic microorganism distribution. 相似文献
330.
Speciation as a screening tool for the determination of heavy metal surface water pollution in the Guadiamar river basin 总被引:7,自引:0,他引:7
The Guadiamar river basin has traditionally received pollutants from two main sources: in its northern section of mining origin, and in its southern section (next to Do?ana National Park) from urban-industrial and agricultural sources. In April 1998, the spill of 6 million m3 of mining wastes (acidic waters and sludge) severely polluted the Guadiamar river basin with heavy metals, which caused serious damage to the local ecosystem. There is a direct association between the physicochemical speciation of an element and its toxicity, biological activity, bioavailability, solubility, etc. This work describes a distribution study of the metals Zn, Cd, Pb and Cu by speciation analysis of surface waters in eleven sampling points of the Guadiamar river basin. Four metal fractions were determined using anodic stripping voltammetry: labile metal forms, H+ exchangeable metal forms, strongly inert forms (associated with organic and inorganic matter in solution), and forms associated with suspended matter. Total concentrations in surface waters followed the trend Zn > Cu > Pb > Cd. The speciation study showed that Zn and Cd were present to a large extent in available forms (labile and H+ exchangeable), while Pb and Cu were found mostly in the less available forms (strongly inert). Moreover, the available forms were found in the northern section (mining pollution) and the strongly inert forms in the southern section (urban, industrial and agricultural pollution). These results can illustrate the potential value of speciation to discern between different sources of pollution. 相似文献