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   93907篇
  免费   1227篇
  国内免费   1101篇
安全科学   3844篇
废物处理   3507篇
环保管理   14379篇
综合类   21117篇
基础理论   26744篇
环境理论   72篇
污染及防治   16169篇
评价与监测   5683篇
社会与环境   4137篇
灾害及防治   583篇
  2022年   823篇
  2021年   827篇
  2020年   656篇
  2019年   863篇
  2018年   1224篇
  2017年   1257篇
  2016年   2203篇
  2015年   1836篇
  2014年   2563篇
  2013年   9208篇
  2012年   2366篇
  2011年   2814篇
  2010年   3350篇
  2009年   3497篇
  2008年   2422篇
  2007年   2218篇
  2006年   2537篇
  2005年   2496篇
  2004年   2771篇
  2003年   2611篇
  2002年   2163篇
  2001年   2449篇
  2000年   2041篇
  1999年   1554篇
  1998年   1376篇
  1997年   1370篇
  1996年   1504篇
  1995年   1606篇
  1994年   1486篇
  1993年   1338篇
  1992年   1336篇
  1991年   1310篇
  1990年   1253篇
  1989年   1220篇
  1988年   1065篇
  1987年   1000篇
  1986年   998篇
  1985年   1066篇
  1984年   1163篇
  1983年   1170篇
  1982年   1176篇
  1981年   1099篇
  1980年   938篇
  1979年   935篇
  1978年   830篇
  1977年   721篇
  1976年   639篇
  1975年   610篇
  1973年   652篇
  1972年   648篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Collaborative policy making has become increasingly significant in environmental management, but it is often evaluated by whether or not agreement is reached and implemented. The most important outcomes of such policy dialogues are often invisible or undervalued when seen through the lens of a traditional, modernist paradigm of government and accountability. These dialogues represent a new paradigm of governance that can be best understood in the light of a complex adaptive system model of society. From this perspective collaborative policy making is a way of making a system more flexible, adaptive and intelligent. The authors document such outcomes in three cases of water policy making in California, including the San Francisco Estuary Project, the CALFED Bay-Delta Program and the Sacramento Area Water Forum. The outcomes include social and political capital, agreed-on information, the end of stalemates, high-quality agreements, learning and change, innovation and new practices involving networks and flexibility.  相似文献   
53.
From 1988 to 1991, we studied the postfledging dispersal of 31 radio-tagged White-crowned Pigeons ( Columba leucocephala ) from three natal keys in Florida Bay. Immature birds dispersed from the natal keys at 26–45 days after batching, and most young dispersed more than 20 km during the first 10 days postdispersal. Dispersing birds flew either north to the Florida mainland or east to northeast to the mainline Florida Keys. On the mainland, immature birds fed nearly exclusively within Everglades National Park or an adjacent state wildlife management area. On the mainline keys, White-crowned Pigeons selectively used 5.01–20 ha forest fragments (p < 0.10) during the first 72 hours postdispersal. After this period, dispersing birds showed no preference among fragment size classes but used deciduous seasonal forests more frequently than suburban habitat(p < 0.10). The spatial pattern of dispersal on the mainline keys suggests that, during the first 72 hours postdispersal. White-crowned Pigeons are not able to reach northern Key Largo, where 69% of the deciduous seasonal forests are protected in state or federal ownership. Protection of large forest fragments, especially on southern Key Largo, should be a priority for maintaining populations of White-crowned Pigeons. These forests provide a series of "stepping stones" that enable dispersing immature White-crowned Pigeons to fly to more distant areas where habitat availability is less restricted. This species is threatened in Florida and may play an important role in maintaining plant species diversity in the seasonal deciduous forests of south Florida by dispersing seeds of at least 37 species of trees and shrubs. Protection of sufficient habitat to allow successful postfledging dispersal of this important seed disperser will also protect the ecosystem's biodiversity.  相似文献   
54.
Ligustrum lucidum Ait. f. tricolor (Rehd.) Rehd. in relation to atmospheric pollutants in Córdoba city, Argentina. The study area receives regional pollutants and was categorized taking into account traffic level, industrial density, type of industry, location of the sample point in relation to the street corner, treeless condition, and topographic level. Dried weight/fresh weight ratio (DW/FW) and specific leaf area (SLA) were calculated, and concentrations of chlorophylls, carotenoids, total sulfur, soluble proteins, malondialdehyde (MDA), and hydroperoxy conjugated dienes (HPCD) were determined in leaf samples. Sulfur content correlates positively with traffic density and SLA correlates negatively with some combinations of the categorical variables; MDA correlates positively with topographic level and total protein concentration correlates negatively with treeless condition. On the basis of our results, traffic, location of trees, type of industry, situation of a tree with respect to others, and topographic level are the environmental variables to bear in mind when selecting analogous sampling points in a passive monitoring program. An approximation to predict tree injury may be obtained by measuring DW/FW ratio, proteins, pigments, HPCD, and MDA as they are responsible for the major variability of data.  相似文献   
55.
56.
The amounts of total NH 4 + detected in the external media in which Phascolosoma arcuatum had been exposed to various periods of anoxia were significantly greater than those in which the worms were exposed to normoxia for a similar period. The increased NH 4 + production by P. arcuatum during anoxic exposure was unlikely to be due to an increased catabolism of adenine nucleotides or urea. In contrast, there were significant decreases in the concentrations of several free amino acids in the coelomic plasma and body tissues of individuals during the 48 h of anoxic exposure. The amount of NH 4 + produced by the anoxic P. arcuatum could be accounted for by the decreases in the concentrations of aspartate or glycine. Increases in the catabolism of free amino acids (FAA), leading to the increased production of NH 4 + , in P. arcuatum during anoxia were supported by the detection of significant changes in the kinetic properties of glutamate dehydrogenase (GDH), in the deaminating direction, from worms exposed to anoxia for 48 h. The apparent increase in the affinity of GDH from the anoxic worm to glutamate would bring about a greater deaminating activity at physiological concentrations of ths substrate. P. arcuatum used in these experiments were collected from the mangrove swamp at Mandai, Singapore between 1990 and 1993.  相似文献   
57.
58.
The two studies reported further test reversal theory hypotheses concerning human psychological responses to different types of settings and environmental events on an Asian sample. In study 1, individuals in four settings representing different combinations of metamotivational state and arousal level (telic and paratelic/low arousal; telic and paratelic/high arousal) completed the telic state measure (TSM; Svebak & Murgatroyd, 1985). Significant differences between participants' mean scores across the four settings were obtained for TSM items serious–playful, planning–spontaneous, felt arousal, preferred arousal, effort and arousal discrepancy. In study 2 different environmental events in the same setting (changes in reading tasks), used in a crossover design, were used to induce reversals in individuals' operative metamotivational states. The results obtained from TSM scores pretask 1, between tasks and posttask 2. indicated significant time-of-testing interaction effects on the TSM serious–playful, planning–spontaneous and effort items. In addition, a main effect for TSM felt arousal was found. These results showed that reversals in metamotivational states were induced by the environmental event and that felt arousal scores increased across the three administrations of the TSM.  相似文献   
59.
60.
In a population of crested tits in Belgium, one out of three breeding males participated in nest-building. Since variation in the amount of nest-building among 11 building males was low, analysis of male nest-building allowed a logistic regression design. The probability of building increased with male condition and for late nests. The effect of male condition decreased with date, and date was the only factor predicting nest-building for repeat broods. The effect of male condition on nest-building suggests that building entails important costs for males. Based on correlative data, we argue that building by males shortens the interval between the start of nest-building and the onset of egg-laying by about 5 days. Since clutch size, incubation and nestling time did not differ between early and late broods, male nest-building apparently affects fledging date. Since early fledgers (early dispersers) are more likely to settle in future winter flocks, building behaviour by crested tit males should be favoured by natural selection. So far, male nest-building in hole-breeding birds might have been overlooked due to the widespread use of artificial nest-boxes in behavioural studies.  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