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   857篇
  免费   33篇
  国内免费   9篇
安全科学   30篇
废物处理   19篇
环保管理   312篇
综合类   93篇
基础理论   256篇
污染及防治   128篇
评价与监测   34篇
社会与环境   17篇
灾害及防治   10篇
  2023年   5篇
  2022年   17篇
  2021年   14篇
  2020年   24篇
  2019年   18篇
  2018年   21篇
  2017年   40篇
  2016年   30篇
  2015年   23篇
  2014年   33篇
  2013年   53篇
  2012年   44篇
  2011年   50篇
  2010年   40篇
  2009年   33篇
  2008年   41篇
  2007年   39篇
  2006年   37篇
  2005年   23篇
  2004年   36篇
  2003年   34篇
  2002年   29篇
  2001年   19篇
  2000年   13篇
  1999年   15篇
  1998年   13篇
  1997年   16篇
  1996年   12篇
  1995年   11篇
  1994年   11篇
  1993年   13篇
  1992年   10篇
  1991年   11篇
  1990年   7篇
  1989年   12篇
  1988年   4篇
  1987年   9篇
  1986年   6篇
  1985年   4篇
  1984年   2篇
  1983年   5篇
  1982年   6篇
  1980年   3篇
  1979年   3篇
  1977年   2篇
  1976年   2篇
  1975年   1篇
  1974年   1篇
  1971年   1篇
  1969年   1篇
排序方式: 共有899条查询结果,搜索用时 187 毫秒
181.
ABSTRACT: There is a growing literature on the resolution of natural resources conflicts. Much of it is practical, focusing on guidelines for hands-on negotiation. This literature can be a guide in water conflicts. This is especially true for negotiations over new environmental values such as instream flow. The concepts of competitive, cooperative, and integrative styles of conflict resolution are applied to three cases of water resource bargaining. Lessons for the effective use of these ideas include: break a large number of parties into small working groups, approach value differences in small steps, be cautious in the presence of an attentive public, keep decisions at the local level, and understand the opponent's interests.  相似文献   
182.
183.
184.
This case study on the Sifnos island, Greece, assesses the main factors controlling vegetation succession following crop abandonment and describes the vegetation dynamics of maquis and phrygana formations in relation to alternative theories of secondary succession. Field survey data were collected and analysed at community as well as species level. The results show that vegetation succession on abandoned crop fields is determined by the combined effects of grazing intensity, soil and geological characteristics and time. The analysis determines the quantitative grazing thresholds that modify the successional pathway. Light grazing leads to dominance by maquis vegetation while overgrazing leads to phryganic vegetation. The proposed model shows that vegetation succession following crop abandonment is a complex multi-factor process where the final or the stable stage of the process is not predefined but depends on the factors affecting succession. An example of the use of succession models and disturbance thresholds as a policy assessment tool is presented by evaluating the likely vegetation impacts of the recent reform of the Common Agricultural Policy on Sifnos island over a 20–30-year time horizon.  相似文献   
185.
The implementation and certification of quality, environmental and occupational health and safety management systems have become a priority for many organizations. They are viewed as symbol for success and prerequisite for survival. However, it has been proved to be difficult to operate multiple parallel management systems covering quality, environment, and occupational health and safety and to ensure their alignment with the organization's strategy. To investigate the current status of integrated management system (IMS), a structured questionnaire survey was administrated. It is concluded that the major problems for enterprises to operate multiple parallel management systems include: it causes complexity of internal management, it lowers management efficiency, it incurs cultural incompatibility, it causes employee hostility, and increases management costs. The survey also examined the internal and external factors that affect the implementation of IMS. The internal factors include: (1) human resources, (2) organizational structure, (3) company culture, and (4) understanding and perception. The external factors consist of: (1) technical guidance, (2) certification bodies, (3) stakeholders and customers, and (4) the institutional environment. The article proposes a multi-level synergy model (strategic synergy, organizational structural-resource-cultural synergy, and documentation synergy) for an effective implementation of IMS.  相似文献   
186.
The distributions and diets of the six most abundant species of teleost in the shallows of a large south-western Australian estuary were examined from samples collected between March 1988 and February 1989. Fish were collected monthly by seine net from over bare sand and from within patchy and dense areas of the aquatic macrophyte Ruppia megacarpa. Their gut contents were compared with samples of the benthos and plankton collected from each of these three habitat types. The densities of the atherinids Leptatherina wallacei and Atherinosoma elongata and of the goby Favonigobius suppositus were greatest in dense R. megacarpa, whereas those of the atherinid L. presbyteroides and the goby F. lateralis were greatest over bare sand. The density of the goby Pseudogobius olorum was greater in patchy R. megacarpa than in the other two habitat types. The gut contents of each of the six species was dominated by crustaceans and/or polychaetes, with detritus also making a major contribution to the diet of P. olorum and F. lateralis. The relative proportions of prey items in the guts of fish in a particular habitat corresponded to the preys' relative occurrence in the environment. This indicates that the fish had been feeding predominantly in one particular habitat prior to capture. Within each habitat type, the six species partitioned the available food, the major components of the diet of each species being different. The gobiid species fed mainly on the benthos and the atherinids typically fed higher in the water column; A. elongata and P. olorum tended to be less selective as to where they foraged. There were no consistent differences in either the dietary breadth or the fullness of the guts of any species among habitat types.  相似文献   
187.
W. White  N. Hall  I. Potter 《Marine Biology》2002,141(6):1153-1164
The lengths-at-age of individuals of the nervous shark Carcharhinus cautus in Shark Bay, Western Australia, have been determined and used to explore the types of situation when it might be advisable to shift from employing a von Bertalanffy equation to a more complex equation for describing the growth of this species and of elasmobranchs in general. The reproductive biology of C. cautus was also examined in order to construct curves for describing growth throughout life from conception as well as from parturition. The presence, in November and early December, of fresh bite marks on the sides of mature females and of a very high proportion of spent individuals among mature males indicate that C. cautus copulates in late October/early November. Ovulation and conception occur in late November/early December and parturition takes place approximately 11 months later. Since mature non-pregnant females contain vitellogenic ova for 12-13 months, i.e. from November or December to the following December, and mature pregnant females contain embryos for 11 months, i.e. from December to October, C. cautus has a biennial reproductive cycle. By parturition, the females and males of C. cautus had reached ~28% and 32% of their lengths at their maximum observed ages, respectively. The maximum recorded total lengths and ages of females and males of C. cautus were 133 cm and 16 years and 111 cm and 12 years, respectively. Females and males reached maturity at ~101 and ~91 cm, respectively, and at least 50% of females and males had become mature by the end of their sixth and fourth years of life after parturition, respectively. The three-parameter, von Bertalanffy growth curves provided reasonably good fits to the lengths-at-age of females and males of C. cautus during just postnatal life and throughout the whole of pre- and postnatal life. While the four-parameter, Schnute growth curve significantly improved the fit to these data for both females and males from conception and for females from parturition, it was recognised that the likelihood ratio test is very sensitive when, as in these cases, there are a large number of data points. A number of interrelated factors were thus taken into account when discussing circumstances when it might be appropriate to switch from using a von Bertalanffy growth curve to the more complex Schnute growth curve.  相似文献   
188.
A Model of Intertemporal Emission Trading, Banking, and Borrowing   总被引:2,自引:0,他引:2  
This paper provides a general treatment of emission trading, banking, and borrowing in an intertemporal, continuous-time model. Using optimal-control theory, the decentralized behavior of firms is shown to lead to the least-cost solution attainable under joint-cost minimization. Explicit solutions for the time paths of emissions and permit prices are derived when firms are allowed to both bank and borrow and when firms are only allowed to bank emission permits. The policy implications of emission banking and borrowing are discussed.  相似文献   
189.
Fish were collected by gill nets from the deeper waters of the Entrance Channel, basins and rivers of the large Peel-Harvey estuarine system (south-western Australia) in the wet (June to November) and dry (December to May) periods between August 1979 and July 1981. Simple-regression analysis showed that the number of species, abundance and biomass of fish in the rivers rose with increases in the salinity and temperature of both the surface and bottom of the water column. No such significant correlations were found in the Entrance Channel andbasins (Peel Inlet and Harvey Estuary), where salinity changes were far less marked. The number of species at sites throughout the estuary was inversely correlated with distance from the estuary mouth. Multiple-regression equations showed that, compared with the other environmental variables tested, bottom salinity had a greater influence on the nunber of species and abundance both in the rivers and in the system as a whole. These results indicate that salinity has a greater effect on the fauna in the deeper waters than in the shallows (cf. Loneragan et al., 1986). The larger fish which characterise the deeper waters may thus be less tolerant to low salinities than the smaller fish typically found in the shallows. Both classification and ordination separated the faunal composition of the rivers from those of the Entrance Channel and basins. The fauna of the two narrow and deeper sites in the rivers separated into wet- and dry-period components. Differences between the faunal composition of the riverine regions and those of the Entrance Channel and basins have been related to the much more variable and lower minimum salinities in the rivers. Species characteristic of the rivers included Amniataba caudavittatus, which is estuarine sensu stricto in south-western Australia, the semianadromous Nematalosa vlaminghi and the highly euryhaline Mugil cephalus. The indicator species for the Entrance Channel and basins were all marine species (Cnidoglanis macrocephalus, Hyporhamphus melanochir, Gerres subfasciatus and Pomatomus saltator).  相似文献   
190.
The dietary compositions and breadths of sequential 50 mm size classes of the six whiting species found in nearshore (<1.5 m), shallow inner-shelf (5 to 15 m) and/or deep inner-shelf (20 to 35 m) waters of the lower west coast of Australia were determined. Comparisons between the results of principal components analysis of head and mouth dimensions and the dietary compositions of Sillago bassensis, S. vittata, S. burrus, S. schomburgkii, S. robusta and Sillaginodespunctata suggests that any differences in the dietary composition of similar-sized representatives of different species, when they occur in the same habitat, are more likely to be due to differences in foraging behaviour than mouth morphology. Classification, ordination and Schoener's overlap indices showed that, in nearshore waters, the juveniles of Sillago bassensis, which colonise relatively exposed areas, have a different diet to those of the smallest representatives of the other whiting species that occupy more sheltered habitats. S. bassensis consumes mainly amphipods, whereas the smaller representatives of S. vittata, S. burrus, S. schomburgkii and Sillaginodes punctata ingest large volumes of copepods, which are typically abundant in protected nearshore waters. Although the mouth dimensions of S. punctata tend to be smaller than those of Sillago schomburgkii, the larger individuals of the former species ingest greater quantities of larger prey, such as crabs and carid shrimps. As S. bassensis, S. vittata and S. burrus increase in size and migrate out into shallow inner-shelf waters, the latter two species tend to concentrate more on benthic prey, while the former species ingests fauna that is more epibenthic. The largest S. bassensis subsequently migrate out into deep inner-shelf waters, where they co-occur with S. robusta, which is restricted to those waters. In these waters, S. bassensis feeds to a far greater extent on large benthic prey, whereas S. robusta consumes a greater quantity of small epibenthic crustaceans, differences that reflect the far larger lengths of the former species in that region. The above data emphasise that the distribution and ontogenetic movements of the six abundant species of whiting play a major role in facilitating a partitioning of food resources amongst these species found in coastal waters of the lower west coast of Australia. Received: 7 October 1996 / Accepted: 31 January 1997  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