全文获取类型
收费全文 | 351篇 |
免费 | 5篇 |
专业分类
安全科学 | 8篇 |
废物处理 | 1篇 |
环保管理 | 17篇 |
综合类 | 250篇 |
基础理论 | 50篇 |
污染及防治 | 23篇 |
评价与监测 | 3篇 |
社会与环境 | 4篇 |
出版年
2018年 | 5篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 15篇 |
2011年 | 5篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 8篇 |
2003年 | 9篇 |
2002年 | 4篇 |
2000年 | 5篇 |
1997年 | 4篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1963年 | 6篇 |
1961年 | 5篇 |
1960年 | 4篇 |
1959年 | 4篇 |
1958年 | 7篇 |
1957年 | 8篇 |
1956年 | 8篇 |
1955年 | 7篇 |
1954年 | 8篇 |
1948年 | 3篇 |
1946年 | 3篇 |
1943年 | 6篇 |
1942年 | 3篇 |
1940年 | 8篇 |
1939年 | 10篇 |
1937年 | 3篇 |
1936年 | 4篇 |
1935年 | 3篇 |
1934年 | 4篇 |
1933年 | 5篇 |
1931年 | 11篇 |
1930年 | 9篇 |
1927年 | 3篇 |
1925年 | 6篇 |
1924年 | 3篇 |
1923年 | 8篇 |
1922年 | 3篇 |
1921年 | 8篇 |
1920年 | 5篇 |
1914年 | 3篇 |
排序方式: 共有356条查询结果,搜索用时 31 毫秒
281.
Large males dominate: ecology,social organization,and mating system of wild cavies,the ancestors of the guinea pig 总被引:1,自引:0,他引:1
Matthias Asher Tanja Lippmann Jörg T. Epplen Cornelia Kraus Fritz Trillmich Norbert Sachser 《Behavioral ecology and sociobiology》2008,62(9):1509-1521
Ecological factors differently affect male and female animals and thereby importantly influence their life history and reproductive
strategies. Caviomorph rodents are found in a wide range of habitats in South America and different social and mating systems
have evolved in closely related species. This permits to study the impact of ecological factors on social evolution. In this
study, we investigated the social organization and the mating system of the wild cavy (Cavia aperea), the ancestor of the domestic guinea pig, in its natural habitat in Uruguay. Based on our laboratory investigations, we
expected a polygynous system with large males controlling access to females. Results from radiotelemetry and direct observations
showed that females occupied small stable home ranges which were largely overlapped by that of one large male, resulting in
a social organization of small harems. In some cases, small satellite males were associated with harems and intermediate-sized
roaming males were occasionally observed on the study site. However, microsatellite analyses revealed that offspring were
exclusively sired by large males of the same or neighboring harems, with a moderate degree of multiple paternity (13–27%).
Thus, the mating system of C. aperea can be described as polygynous and contrasts with the promiscuous organization described for other species of cavies (Cavia magna, Galea musteloides and Microcavia australis) living under different ecological conditions. Our findings stress the strong impact of environmental factors on social evolution
in Caviomorphs as resource distribution determines female space use and, thereby, the ability of males to monopolize females.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
282.
Pierrick Blanchard Rodolphe Sabatier Hervé Fritz 《Behavioral ecology and sociobiology》2008,62(12):1863-1868
Theory predicts that individuals at the periphery of a group should be at higher risk than their more central conspecifics
since they would be the first to be encountered by an approaching terrestrial predator. As a result, it is expected that peripheral
individuals display higher vigilance levels. However, the role of conspecifics in this “edge effect” may have been previously
overlooked, and taking into account the possible role of within-group competition is needed. Vigilance behavior in relation
to within-group spatial position was studied in impalas (Aepyceros melampus) feeding on standardized patches. We also controlled for food distribution in order to accurately define a “central” as opposed
to a “peripheral” position. Our data clearly supported an edge effect, with peripheral individuals spending more time vigilant
than their central conspecifics. Data on social interactions suggest that it was easier for a foraging individual to defend
its feeding patch with its head lowered, and that more interactions occurred at the center of the group. Together, these results
indicate that central foragers may reduce their vigilance rates in response to increased competition. Disentangling how the
effects of competition and predation risk contribute to the edge effect requires further investigations. 相似文献
283.
Effective management of invasive species requires that we understand the mechanisms determining community invasibility. Successful invaders must tolerate abiotic conditions and overcome resistance from native species in invaded habitats. Biotic resistance to invasions may reflect the diversity, abundance, or identity of species in a community. Few studies, however, have examined the relative importance of abiotic and biotic factors determining community invasibility. In a greenhouse experiment, we simulated the abiotic and biotic gradients typically found in vernal pools to better understand their impacts on invasibility. Specifically, we invaded plant communities differing in richness, identity, and abundance of native plants (the "plant neighborhood") and depth of inundation to measure their effects on growth, reproduction, and survival of five exotic plant species. Inundation reduced growth, reproduction, and survival of the five exotic species more than did plant neighborhood. Inundation reduced survival of three species and growth and reproduction of all five species. Neighboring plants reduced growth and reproduction of three species but generally did not affect survival. Brassica rapa, Centaurea solstitialis, and Vicia villosa all suffered high mortality due to inundation but were generally unaffected by neighboring plants. In contrast, Hordeum marinum and Lolium multiflorum, whose survival was unaffected by inundation, were more impacted by neighboring plants. However, the four measures describing plant neighborhood differed in their effects. Neighbor abundance impacted growth and reproduction more than did neighbor richness or identity, with growth and reproduction generally decreasing with increasing density and mass of neighbors. Collectively, these results suggest that abiotic constraints play the dominant role in determining invasibility along vernal pool and similar gradients. By reducing survival, abiotic constraints allow only species with the appropriate morphological and physiological traits to invade. In contrast, biotic resistance reduces invasibility only in more benign environments and is best predicted by the abundance, rather than diversity, of neighbors. These results suggest that stressful environments are not likely to be invaded by most exotic species. However, species, such as H. marinum, that are able to invade these habitats require careful management, especially since these environments often harbor rare species and communities. 相似文献
284.
The dissolved organic matter in aquatic systems consists of a heterogeneous mixture of compounds with wide ranging chemical properties and diverse origins. the presence of organic matter (OM) in surface and ground waters has important implications with regard to the mobility and therefore fate of many potential organic and inorganic pollutants. the majority of the analytical approaches in current use require exhaustive pre-treatment steps which may lead to the formation of artefacts within the sample. an analytical technique based upon gel permeation chromatography is proposed as a more reliable procedure for the characterisation of naturally occurring dissolved organic matter. 相似文献
285.
Michelle E. Lander Lowell W. Fritz Devin S. Johnson Miles G. Logsdon 《Marine Biology》2013,160(1):195-209
The recovery plan for Steller sea lions (SSL; Eumetopias jubatus) suggests critical habitat should be enhanced to incorporate the spatio-temporal variation in dynamic oceanographic features that influence the prey and survival of SSL. It is necessary, therefore, to determine which features affect SSL. Demographics for sub-regions of the endangered, western stock of SSL were examined with respect to corresponding average, maximum, and variance of chlorophyll-a data (SeaWIFS), a proxy for primary productivity. Overall, SSL trends (2000–2008) and pup productivity (1999–2009) were related to maximum values of chl-a in critical habitat. Additionally, conditions in critical habitat appeared worse in areas of decline (i.e., dispersed patterns of chl-a hotspots and greater distances from SSL sites to productive areas). Although there may be a low feasibility of mitigating the effects of dynamic features on the recovery of SSL, the interactive effects of primary productivity and other stressors should be investigated for safeguarding their prey. 相似文献
286.
Work characteristics such as time pressure and job control can be experienced as a challenge that is positively associated with performance‐related behaviors. Using experience‐sampling data from 149 employees, we examined the relationships between these work characteristics and creativity and proactive behavior on a daily level. Results from multilevel analyses indicate that time pressure and job control are perceived as challenging, and that challenge appraisal in turn is related to daily creativity and proactive behavior. Furthermore, cross‐level mediation analyses revealed that daily work characteristics act as the mechanism underlying the relationships between chronic work characteristics and challenge appraisal. This study supports the view of time pressure as a challenge‐related stressor that leads to favorable outcomes. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
287.
Carbon fixation and coccolith detachment in the coccolithophore Emiliania huxleyi in nitrate-limited cyclostats 总被引:1,自引:0,他引:1
J. J. Fritz 《Marine Biology》1999,133(3):509-518
This study addresses carbon fixation and coccolith production and detachment in the cosmopolitan species Emiliania huxleyi (Lohmann) Hay et Mohler, under conditions of nitrate limitation and high light typical of surface water in the ocean. Cells
were grown under controlled growth conditions using nitrate-limited cyclostat cultures at four growth rates between 0.2 and
0.7 d−1 in 1995. Both photosynthesis and calcification rates increased with growth rate. Coccolith dimensions remained constant at
all cell growth rates. Specific rates of coccolith detachment also increased linearly with cell-specific growth rate at a
ratio not significantly different from 1.00. Estimates of coccolith carbon content decreased with increasing cell growth rates.
Received: 18 March 1997 / Accepted: 8 October 1998 相似文献
288.
Steven C. Richtsmeier Neil Goldstein Fritz Bien Chris Schuch Jack Buckley Robert R. Bennett 《Journal of the Air & Waste Management Association (1995)》2013,63(12):981-988
Abstract An instrumentation system employing an RPV (remotely piloted vehicle) platform was developed for temporally and spatially resolved air pollution measurements, and was used to measure the evolution of gas-phase HC1 in exhaust clouds from a solid rocket motor firing and fuel pit burns. A thermistor and a sensitive (ppmv-level), rapid-response (<0.1 sec) infrared absorption sensor for HC1 were mounted in a flow channel in the RPV, permitting concentration and temperature measurements to be made in the cloud on a several-meter scale. The RPV system was flown in a series of field tests at Thiokol Corporation’s Elkton, MD division to evaluate the HC1 content of the exhaust products of a new Mg-based fuel formulation. Measurements were made in the clouds from Al-based and Mg-based solid fuel pit burns and a Mg-fueled motor firing over periods of several minutes. Elevated temperatures and HC1 concentrations were found to be temporally correlated with video images of the particulate cloud. Cl originating from the ammonium perchlorate oxidizer appeared in the exhaust as HC1 in each of the tests. Both the macroscopic and local cloud parameters indicate that the Mg-based fuel may provide some reduction in HC1 concentration compared to the standard Al-based fuel. 相似文献
289.
Environmental Management - Cattle degrade streams by increasing sediment, nutrient, and fecal bacteria levels. Riparian fencing is one best management practice that may protect water quality within... 相似文献
290.