全文获取类型
收费全文 | 5308篇 |
免费 | 43篇 |
国内免费 | 25篇 |
专业分类
安全科学 | 81篇 |
废物处理 | 336篇 |
环保管理 | 385篇 |
综合类 | 786篇 |
基础理论 | 1115篇 |
环境理论 | 4篇 |
污染及防治 | 1827篇 |
评价与监测 | 490篇 |
社会与环境 | 336篇 |
灾害及防治 | 16篇 |
出版年
2023年 | 55篇 |
2022年 | 163篇 |
2021年 | 147篇 |
2020年 | 62篇 |
2019年 | 77篇 |
2018年 | 182篇 |
2017年 | 136篇 |
2016年 | 248篇 |
2015年 | 147篇 |
2014年 | 282篇 |
2013年 | 475篇 |
2012年 | 319篇 |
2011年 | 348篇 |
2010年 | 257篇 |
2009年 | 218篇 |
2008年 | 299篇 |
2007年 | 305篇 |
2006年 | 264篇 |
2005年 | 199篇 |
2004年 | 163篇 |
2003年 | 140篇 |
2002年 | 130篇 |
2001年 | 104篇 |
2000年 | 69篇 |
1999年 | 49篇 |
1998年 | 24篇 |
1997年 | 20篇 |
1996年 | 11篇 |
1995年 | 37篇 |
1994年 | 29篇 |
1993年 | 19篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1985年 | 8篇 |
1967年 | 8篇 |
1966年 | 13篇 |
1965年 | 15篇 |
1964年 | 30篇 |
1963年 | 12篇 |
1962年 | 18篇 |
1961年 | 13篇 |
1960年 | 10篇 |
1959年 | 26篇 |
1958年 | 28篇 |
1957年 | 19篇 |
1956年 | 13篇 |
1955年 | 19篇 |
排序方式: 共有5376条查询结果,搜索用时 687 毫秒
741.
742.
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
743.
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
744.
Escalante M Rodríguez-Malaver AJ Araujo E González AM Rojas OJ Peñaloza N Bullón J Lara MA Dmitrieva N Pérez-Pérez E 《Journal of environmental biology / Academy of Environmental Biology, India》2005,26(4):709-718
One of the limitations of the biodegradation of hydrophobic chemical compounds, like lignins, is their low solubility in the aqueous solution where this process takes place. To resolve this problem, surfactants have been used to improve the solubility of these hydrophobic compounds. In this investigation, we studied the effect of surfactants (anionic, cationic, and non-ionic) on the treatment of Kraft black liquor with Fenton's reagent. In the Fenton reaction, H2O2 (two different concentrations, 10 mM and 20 mM), FeCl2 (1 mM) and surfactant solution (10%) were used. Black liquor degradation was determined by UV/Visible spectrophotometry and by measuring phenolic groups. In the presence of Fenton's reagent, the optimum conditions for the oxidative degradation of black liquor were 10 mM H2O2, 1 microL of 10% solution of anionic surfactant (SDS). The importance of the use of surfactants for preparing black liquor for subsequent Fenton's reagent-mediated degradation was discussed. 相似文献
745.
Elie Gaget Diego Pavón-Jordán Alison Johnston Aleksi Lehikoinen Wesley M. Hochachka Brett K. Sandercock Alaaeldin Soultan Hichem Azafzaf Nadjiba Bendjedda Taulant Bino Luka Božič Preben Clausen Mohamed Dakki Koen Devos Cristi Domsa Vitor Encarnação Kiraz Erciyas-Yavuz Sándor Faragó Teresa Frost Clemence Gaudard Lívia Gosztonyi Fredrik Haas Menno Hornman Tom Langendoen Christina Ieronymidou Vasiliy A. Kostyushin Lesley J. Lewis Svein-Håkon Lorentsen Leho Luigujõe Włodzimierz Meissner Tibor Mikuska Blas Molina Zuzana Musilová Viktor Natykanets Jean-Yves Paquet Nicky Petkov Danae Portolou Jozef Ridzoň Samir Sayoud Marko Šćiban Laimonas Sniauksta Antra Stīpniece Nicolas Strebel Norbert Teufelbauer Goran Topić Danka Uzunova Andrej Vizi Johannes Wahl Marco Zenatello Jon E. Brommer 《Conservation biology》2021,35(3):834-845
Climate warming is driving changes in species distributions and community composition. Many species have a so-called climatic debt, that is, shifts in range lag behind shifts in temperature isoclines. Inside protected areas (PAs), community changes in response to climate warming can be facilitated by greater colonization rates by warm-dwelling species, but also mitigated by lowering extirpation rates of cold-dwelling species. An evaluation of the relative importance of colonization-extirpation processes is important to inform conservation strategies that aim for both climate debt reduction and species conservation. We assessed the colonization-extirpation dynamics involved in community changes in response to climate inside and outside PAs. To do so, we used 25 years of occurrence data of nonbreeding waterbirds in the western Palearctic (97 species, 7071 sites, 39 countries, 1993–2017). We used a community temperature index (CTI) framework based on species thermal affinities to investigate species turnover induced by temperature increase. We determined whether thermal community adjustment was associated with colonization by warm-dwelling species or extirpation of cold-dwelling species by modeling change in standard deviation of the CTI (CTISD). Using linear mixed-effects models, we investigated whether communities in PAs had lower climatic debt and different patterns of community change than communities outside PAs. For CTI and CTISD combined, communities inside PAs had more species, higher colonization, lower extirpation, and lower climatic debt (16%) than communities outside PAs. Thus, our results suggest that PAs facilitate 2 independent processes that shape community dynamics and maintain biodiversity. The community adjustment was, however, not sufficiently fast to keep pace with the large temperature increases in the central and northeastern western Palearctic. Our results underline the potential of combining CTI and CTISD metrics to improve understanding of the colonization-extirpation patterns driven by climate warming. 相似文献
746.
Nathália Nascimento Thales A. P. West Lisa Biber-Freudenberger Eráclito R. de Sousa-Neto Jean Ometto Jan Börner 《Journal of Land Use Science》2020,15(2-3):127-141
ABSTRACT Deforestation driven by agricultural expansion is a major threat to the biodiversity of the Amazon Basin. Modelling how deforestation responds to environmental policy implementation has thus become a policy relevant scientific undertaking. However, empirical parameterization of land-use/cover change (LUCC) models is challenging due to the high complexity and uncertainty of land-use decisions. Bayesian Network (BN) modelling provides an effective framework to integrate various data sources including expert knowledge. In this study, we integrate remote sensing products with data from farm-household surveys and a decision game to model LUCC at the BR-163, in Brazil. Our ‘business as usual’ scenario indicates cumulative forest cover loss in the study region of 8,000 km2 between 2014 and 2030, whereas ‘intensified law-enforcement’ would reduce cumulative deforestation to 1,600 km2 over the same time interval. Our findings underline the importance of conservation law enforcement in modulating the impact of agricultural market incentives on land cover change. 相似文献
747.
Natalia Yoshida Mariano Castro Cecile du Mortier Alicia Fernández Cirelli 《Environmental Chemistry Letters》2007,5(3):157-160
The increase of intensive bovine production systems in Argentina involves the use of therapeutic agents and growth promoters
that reach the environment through animal excreta. The growth promoter most widely used in Argentina is monensin, an ionophore
polyether antibiotic produced by Streptomyces cinnamoniensis. Here, the behavior of monensin in different solid environmental matrices is analyzed, and preliminary results that suggest
a strong dependence of monensin retention with the organic matter content of the matrix are discussed. 相似文献
748.
The present study describes the emergence pattern of loggerhead sea turtle hatchlings (Caretta caretta) from a nesting beach in Kyparissia Bay (Greece). We try to establish the role played by hatchling biometry, nest relocation
and distance from nest to the sea on this emergence pattern. We surveyed a total of 32 nests, and found long emergence periods
(mean = 6.7 nights). The majority of emergences occurred at night, mainly between 0030 and 0100 hours, and in small groups.
Most of the hatchlings emerged from the nests the first night. We found no clear trend when we studied the effect of hatchling
biometry between successive emergence days. We also found that relocation of the nests did not significantly affect the emergence
pattern. However, we noted that in the relocated nests, hatchlings emerged in smaller groups. Emergence periods were inversely
related to distance from the sea. In short, factors such as climate conditions, relocation and nest distance to the sea appear
to have some effect on the emergence pattern. Therefore, they should be taken into account in both biological studies and
management plans for sea turtle nesting beaches. Our results suggest leaving an extended period between the first emergence
of hatchlings and the excavation of nests by researchers in future studies in the area. 相似文献
749.
To investigate copepod nauplii ingestion rates on phytoplankton, we have adapted the traditional gut fluorescence technique
as it can be used with lower gut pigment concentrations. With the improved technique, laboratory experiments were performed
to estimate functional responses for nauplii of Calanus helgolandicus and Centropages typicus. Nauplii were raised from eggs to copepodites and the experiments were performed with stages NIV-NV. Gut evacuation rates
and ingestion rates were measured on Isochrysis galbana at different concentrations. Specific ingestion rates ranged between 0.038–0.244 μg C μg−1 nauplii C d−1 for C. typicus and 0.041–1.412 μg C μg−1 nauplii C d−1 for C. helgolandicus. Both species showed a type III functional response, reaching a saturation concentration at around 600 μgC l−1 for C. typicus and 800 μgC l−1 for C. helgolandicus.
An erratum to this article can be found at 相似文献
750.
Elasmobranch stock assessment studies are usually made through fisheries surveys data. However, in large marine protected
areas (MPAs) the use of destructive techniques must be dismissed in order to avoid population impacts. In 2005, while conducting
a marine habitat survey in two marine Special Areas of Conservation (Sebadales de Playa de Inglés and Franja Marina de Mogán)
in south Gran Canary Island (Canary Islands, Spain) with underwater towed video (UTV) and underwater visual census (UVC) transects,
we recognized the opportunity rose to assess elasmobranch populations through UTV. Number of observed species and specimens,
overall field work effort and total surveyed area were determined and compared between methods. Mean observations per day
per unit of time (MOPUT) and mean observations per day per unit of surveyed area (MOPUA) were also compared through Mann–Whitney
rank sum statistical test (α = 0.05). Data analysis demonstrated that UTV is a very useful tool to rapidly assess elasmobranch
populations in large MPAs in good visibility underwater environments. It can assess larger areas than UVC with the same effort
(statistically significant difference found for the MOPUT; p =< 0.001), leading to more observed species (5 vs 2) and specimens (46 vs 3) per day of work, with no loss in resolution power (MOPUA values were not significantly different between UTV and UVC;
p = 0.104). 相似文献