首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2628篇
  免费   27篇
  国内免费   38篇
安全科学   97篇
废物处理   82篇
环保管理   363篇
综合类   536篇
基础理论   552篇
环境理论   2篇
污染及防治   727篇
评价与监测   170篇
社会与环境   142篇
灾害及防治   22篇
  2023年   24篇
  2022年   22篇
  2021年   36篇
  2020年   27篇
  2019年   36篇
  2018年   64篇
  2017年   64篇
  2016年   77篇
  2015年   96篇
  2014年   90篇
  2013年   182篇
  2012年   111篇
  2011年   172篇
  2010年   135篇
  2009年   142篇
  2008年   141篇
  2007年   141篇
  2006年   113篇
  2005年   83篇
  2004年   105篇
  2003年   70篇
  2002年   92篇
  2001年   83篇
  2000年   45篇
  1999年   23篇
  1998年   29篇
  1997年   31篇
  1996年   30篇
  1995年   37篇
  1994年   30篇
  1993年   13篇
  1992年   25篇
  1991年   36篇
  1990年   18篇
  1989年   26篇
  1988年   11篇
  1987年   9篇
  1986年   8篇
  1985年   14篇
  1984年   10篇
  1982年   17篇
  1981年   16篇
  1979年   12篇
  1978年   8篇
  1975年   6篇
  1971年   6篇
  1970年   8篇
  1969年   8篇
  1965年   6篇
  1960年   8篇
排序方式: 共有2693条查询结果,搜索用时 46 毫秒
991.
The foredunes form an important element of the line of defence which protects the low-lying parts of the Netherlands from the sea. The foredune of the eastern part of the Wadden island of Terschelling has been managed as a ‘rolling’ foredune to maximize the amount of sand available in times of emergency. Following a decision of the Dutch Government to maintain the coastline of 1990, this foredune will now be stabilized. A plan is made to reshape the morphology of the foredune according to a geomorphological design. A simulation model was developed to produce a Digital Terrain Model with the required geometrical information. The transformation which is on the macro-level scale can be achieved within the envisaged medium-scale planning period of five years only by applying earth-moving machinery, placing fences or planting sand-trapping vegetation.  相似文献   
992.
993.
Monitoring, understanding and modelling carbon emission and fixation fluxes are key actions to guide climate change stakeholders in the application of mitigation strategies. In this study, we use the remote sensing model C-Fix at the local stand scale to improve the integration of algorithms for water and temperature limitation. These new algorithms are applied to estimate net ecosystem productivity in a fully water limited mode.  相似文献   
994.
Allogeneic interactions between Acropora hemprichi (Ehrenberg) colonies were followed in situ up to 18 mo between 1990 and 1992 in Eilat, Red Sea. We established all 21 possible branch pair combinations among seven large colonies in three to eight replicates each (n=92 pairs), in addition in 14 pairs of grafts within-colonies. All isografts resulted in fusion. Allogeneic interactions revealed a variety of effector mechanisms which involved the appearance of dark blue-purple color in the tissues of interacting branch tips (<1 cm), unilateral overgrowths (1.0 to 1.5 mm mo-1 for 1 to 8 mo), rejections, healings, continuous overgrowths, reversals, repeated rejections and more. Direction of overgrowth was usually specific to a given combination of colonies. A hierarchial network of overgrowths was obtained by analyzing overgrowth directions of all pairwise combinations, which included 30 transitive and five nontransitive three-way combinations. These outcomes, similarly to responses of allogeneic encounters recorded from other coral species, show that colonies can respond selectively to different types of allogeneic challenges. It is suggested that corals may have the capacity to distinguish self from nonself by recognizing nonself attributes presented on conspecifics.  相似文献   
995.
Time-depth recorders were attached to immature hawksbills (Eretmochelys imbricata Linnaeus, 1766) residing at the northwestern cliffs of Mona Island, Puerto Rico. Data on diving profiles obtained from four turtles of 32.0 to 53.4 cm straight carapace length revealed strong similarities in behavioral patterns. During daylight hours, turtles were active an average 8.4 h per day, surfacing 3.6% of the time. Length of foraging dives correlated with turtle size, with mean durations ranging from 8.6 to 14.0 min. Foraging dives, with a mean depth of 4.7 m, were associated with feeding on encrusting sponges. At night, turtles were mostly inactive, surfacing 1.8% of the time and with individual mean submergence intervals of between 30.4 and 37.1 min. From the surfacing behavior of turtles making deep and long dives, it is inferred that dives were aerobic, with the turtles making use of oxygen stores in addition to that of the lung.  相似文献   
996.
997.
In the tradition of the study of materials flows through society, the Substance Flow Analysis (SFA) method and its software tool SFINX are presented. SFA aims at providing the relevant information for a country’s overall management strategy regarding single substances or coherent groups of substances. Three modelling techniques and their possibilities and limitations are discussed: Bookkeeping, static modelling, and dynamic modelling. The computer program SFINX can be used for varoius purposes: (1) to obtain an overview of stocks and flows of a substance in, out and through a nation’s economy and environment for a specific year, (2) to trace the origins of specific pollution problems, and (3) to estimate the effectiveness of certain abatement measures. Each application has its own requirements with regard to data and modelling.  相似文献   
998.
  Die geschichtliche Entwicklung der kosmologischen Modelle für den homogen–isotropen Kosmos, beginnend mit Alexander Friedmanns epochalen Arbeiten (1922 und 1924) bis zur heutigen Diskussion aktueller Modelle wird dargestellt. Eine kardinale Rolle spielt die offene Frage: Besteht die Materie des Kosmos zum weit überwiegenden Teil aus nicht–baryonischer (sog. exotischer) Dunkel–Materie oder reicht die gesamte baryonische Materie aus, die aus den bekannten Atomen und Molekülen besteht, um die Entwicklung des Kosmos zu verstehen. Auch von der normalen (baryonischen) Materie im Kosmos ist nur ein geringer Anteil (etwa 20 5 Prozent) in leuchtenden Objekten (Sterne, Gas, Staub) direkt beobachtbar. Im Abschnitt 3 wird der “Einstein–Limit” für die kosmologische Konstante erl?utert und eine leicht einsichtige Herleitung des Zahlenwertes gegeben.  相似文献   
999.
Due to the short residence time of the water in the western Dutch Wadden Sea the ctenophore Pleurobrachia pileus has to be considered as an allochthonous species, which enters the estuary passively from the North Sea. The seasonal occurrence of this species in the Dutch Wadden Sea is a reflection of its abundance in the coatal zone of the North Sea and is characterized by a pronounced spring peak of up to 17000 individuals per 1000 m3 and a lower autumn peak with numbers up to 400 individuals per 1000 m3. Similar to other areas, predation by Beroë gracilis, another ctenophore species, may be a factor in controlling the P. pileus population in this region, although B. gracilis abundance is low. P. pileus is only important as a predator for a short time, i.e. the month of May, when it reaches maximum biomass values of up to 12 00 mgC per 1000 m3. Both the estimated potential consumption rates in comparison with the available food as well as the observed suboptimal growth rate of the population suggest that in the coastal zone of the North Sea area food conditions may not be optimal for P. pileus.  相似文献   
1000.
The development of chronological reference points to which present levels of inorganic pollutants can be compared is increasingly needed. This review is directed toward biological samples which are datable and have been characterized for one or more elements.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号