全文获取类型
收费全文 | 3653篇 |
免费 | 68篇 |
国内免费 | 40篇 |
专业分类
安全科学 | 175篇 |
废物处理 | 144篇 |
环保管理 | 685篇 |
综合类 | 601篇 |
基础理论 | 831篇 |
环境理论 | 3篇 |
污染及防治 | 879篇 |
评价与监测 | 218篇 |
社会与环境 | 180篇 |
灾害及防治 | 45篇 |
出版年
2023年 | 32篇 |
2022年 | 40篇 |
2021年 | 50篇 |
2020年 | 47篇 |
2019年 | 47篇 |
2018年 | 93篇 |
2017年 | 110篇 |
2016年 | 126篇 |
2015年 | 135篇 |
2014年 | 135篇 |
2013年 | 213篇 |
2012年 | 165篇 |
2011年 | 266篇 |
2010年 | 197篇 |
2009年 | 185篇 |
2008年 | 202篇 |
2007年 | 215篇 |
2006年 | 198篇 |
2005年 | 125篇 |
2004年 | 151篇 |
2003年 | 115篇 |
2002年 | 119篇 |
2001年 | 107篇 |
2000年 | 58篇 |
1999年 | 46篇 |
1998年 | 44篇 |
1997年 | 40篇 |
1996年 | 44篇 |
1995年 | 47篇 |
1994年 | 38篇 |
1993年 | 23篇 |
1992年 | 31篇 |
1991年 | 33篇 |
1990年 | 22篇 |
1989年 | 23篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 15篇 |
1970年 | 7篇 |
1969年 | 7篇 |
1967年 | 5篇 |
1965年 | 5篇 |
1960年 | 4篇 |
排序方式: 共有3761条查询结果,搜索用时 78 毫秒
261.
262.
In dune slacks in The Netherlands, a decline of rare mesotrophic basiphilous plant species and their plant communities has
been observed in combination with an increase of more productive systems with common, taller acidophilous plant species. This
has been attributed to both natural and anthropogenic changes. In a humid climate with a precipitation surplus, as in The
Netherlands, the calcium carbonate content of a calcareous soil increases with depth. However, soils in coastal dune slacks,
may have a higher carbonate content in the topsoil horizon than in the underlying layers. Carbonates which buffer the pH can
prolong the presence of mesotrophic basiphilous plant communities which are of high conservation value.
To explain the occurrence of calcareous surface horizons in dune slacks, hydrological and micromorphological analyses were
carried out in three dune slacks. Two slacks are situated on the Wadden Sea islands in the northern part of The Netherlands;
one on Schiermonnikoog and one on Texel. The third slack is situated in the dunes on the island of Goeree in the southwestern
part of The Netherlands. In all three slacks, carbonate occurs as mollusc and gastropod fragments (silt- or sand-sized) and
as micritic nodules in the topsoil layer, due to aeolian deposition and sedimentation by water.In situ carbonate accumulation (calcitans and calcareous crusts) due to CO2 release in inundated and/or capillary rise of calcareous groundwater near, or at the soil surface. Accumulation of carbonate
also occurs as a result of biological activity by algae in the topsoil of the Goeree site. In general, hydrological processes
maintaining high levels of calcareous groundwater are a prerequisite for the maintenance of high carbonate levels in topsoils.
Such levels are necessary for the conservation and management of basiphilous pioneer vegetation. 相似文献
263.
Synergistic Interactions between Habitat Fragmentation and Fire in Evergreen Tropical Forests 总被引:5,自引:0,他引:5
Mark A. Cochrane 《Conservation biology》2001,15(6):1515-1521
Abstract: The growing prevalence of fragmentation and fire in tropical forests makes it imperative to quantify changes in these disturbances and to understand the ways in which they interact across the landscape. I used a multitemporal series of Landsat images to study the incidence and coincidence of fire and fragmentation in two areas of Pará state in the eastern Brazilian Amazon: Tailândia and Paragominase. In both areas, deforestation and forest fires were quantified for time series of 6–10 years. The Tailândia study area typifies a landscape with the herringbone pattern of government-settled colonists, and the Paragominas area is dominated by large cattle ranches. In both areas, over 90% of the forests affected by fire were associated with forest edges. Although most burned forest occurred within 500 m of forest edges, some fires occurred in deep forest, several kilometers from any edge. The obvious synergism between forest fragmentation and fire poses serious risks to tropical ecosystems and has important implications for land management. 相似文献
264.
Jutta M. Schneider Melissa L. Thomas Mark A. Elgar 《Behavioral ecology and sociobiology》2001,49(5):410-415
Male genitalia may facilitate sperm protection by acting as a plug that prevents or hinders future matings. The pedipalps (intromittant organs) of males of the orb-web spider, Nephila plumipes, have a conductor with a peculiarly curved ending and a triangular process near the terminal end. The tip of the conductor, including the process, breaks during most matings and remains inside the female genital tract. We explored the possible function of the conductor as a mating plug using the double-mating sterile-male technique. Our data are not consistent with a plug function because males use only one pedipalp in each mating, thus leaving an unobstructed insemination duct available for future matings; conductors of males mating with virgin females are not more likely to break than those of males mating with mated females, and second males show no preference for used or unused spermathecae. In addition, males that inserted their palp in the insemination duct that contained a tip of the conductor from a previous male obtained a share in the paternity of the female's clutch of eggs. Interestingly, the conductor is more likely to break if it is inserted in an unused spermatheca. We argue that several lines of evidence suggest that the conductor breaks as a result of intersexual conflict over the duration of copulation. 相似文献
265.
266.
The threat-sensitivity hypothesis predicts that prey individuals will increase antipredator behaviors as apparent predator risk increases. An implicit assumption of the threat-sensitivity hypothesis is that predator risk is additive. In other words, all characteristics of a predator that indicate risk should contribute in an additive way to determine the degree of risk-sensitive behavior. We tested this assumption in the laboratory by presenting live predators (green sunfish, Lepomis cyanellus) to groups of western mosquitofish (Gambusia affinis). We examined effects of predator diet, hunger level, and size on predator avoidance and inspection behavior of mosquitofish. Both predator diet and predator hunger level were significant and additive determinants of distance maintained from a predator, resulting in a graded response to combinations of these predator cues. In contrast, whereas predator diet was the most important determinant of general avoidance distances, predator hunger level was more important in determining mosquitofish vertical distribution and inspection behavior. Thus, the relationship between predator cue and the antipredator behavior that it elicits is dependent on which cues and behaviors are examined. Our data suggest that during risky behaviors, such as predator inspection, mosquitofish rely mainly on visual cues (behavior differences between hungry and satiated predators), whereas general avoidance behavior is determined by additive responses from visual and chemical cues. 相似文献
267.
268.
Summary. Chemical defense against herbivores has rarely been investigated for freshwater plants, possibly due to the common misconception
that herbivory on aquatic macrophytes is low and would not select for chemical defenses. In previous work, the freshwater
angiosperm Saururus cernuus was shown to be a low preference food for omnivorous crayfish despite its high nutrient value and relatively soft texture.
We used feeding by the crayfish Procambarus clarkii to guide fractionation of the deterrent lipid-soluble extract of this plant, leading to the identification of seven deterrent
lignoid metabolites, (–)-licarin A, (+)-saucernetin, (–)-dihydroguaiaretic acid, (–)-sauriols A and B, (–)-saucerneol, and
(–)-saucerneol methyl ether. Lignans have been implicated in terrestrial plant chemical defenses as insect growth inhibitors,
insect toxins, nematocides, antibacterial, and antifungal agents. However, these activities have rarely been demonstrated
using ecologically relevant methodologies in terrestrial systems, and never before in freshwater systems. The widespread nature
of lignans amongst very distantly related plants, along with their rich diversity of molecular structure, suggests that they
could play a large role in mediating plant-herbivore interactions. In addition to the lignoid compounds we identified, there
were other compounds present in low concentration or unstable compounds that were deterrent, that did not appear to be lignans,
but that we were unable to identify. This plant thus appears to be defended by a complex mixture of natural products.
Received 6 June 2000; revised 23 August 2000; accepted 2 September 2000 相似文献
269.
Claudia Voelckel Tamara Krügel Klaus Gase Nadja Heidrich Nicole M. van Dam Robert Winz Ian T. Baldwin 《Chemoecology》2001,11(3):121-126
270.
Mark Duffield 《Disasters》2001,25(4):308-320
This article examines aid practice, that is, the public-private contractual networks that link donor governments, UN agencies, military establishments, NGOs, private companies and others, as a relation of global liberal governance. In order to fulfil this function, such networks embody what could be called the 'securitisation' of international assistance. Based upon ideas of human security and ameliorating the effects of poverty and vulnerability reduction, aid is now seen as playing a direct security role. Rather than being concerned with relations between states, the primary aim of this security paradigm is to modulate and change the behaviour of populations within them. In doing so, it is able to exploit the opportunities afforded by privatisation. At the same time, however, aid as security is confronted by its own particular problem of 'governing at a distance'; how can calculations made by leading states be transformed into actions at the global edge when a multitude of private and non-government implementors now intervene? The article concludes by examining the contribution of risk analysis to solving this problem and, especially, the development of new contractual regimes based around technical standardisation, benchmarking and performance auditing. Through such technologies, metropolitan states are learning how to manage the public-private networks of aid practice and, as a result, to govern the borderlands in new ways. 相似文献