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   1930篇
  免费   84篇
  国内免费   218篇
安全科学   196篇
废物处理   117篇
环保管理   933篇
综合类   597篇
基础理论   125篇
污染及防治   99篇
评价与监测   94篇
社会与环境   22篇
灾害及防治   49篇
  2024年   3篇
  2023年   22篇
  2022年   24篇
  2021年   27篇
  2020年   35篇
  2019年   22篇
  2018年   14篇
  2017年   26篇
  2016年   30篇
  2015年   30篇
  2014年   41篇
  2013年   52篇
  2012年   45篇
  2011年   59篇
  2010年   50篇
  2009年   50篇
  2008年   67篇
  2007年   52篇
  2006年   47篇
  2005年   30篇
  2004年   60篇
  2003年   91篇
  2002年   179篇
  2001年   164篇
  2000年   177篇
  1999年   146篇
  1998年   110篇
  1997年   85篇
  1996年   219篇
  1995年   64篇
  1994年   19篇
  1993年   17篇
  1992年   8篇
  1991年   10篇
  1990年   5篇
  1989年   9篇
  1988年   4篇
  1986年   1篇
  1985年   22篇
  1984年   38篇
  1983年   35篇
  1982年   4篇
  1981年   2篇
  1980年   10篇
  1978年   6篇
  1977年   2篇
  1975年   2篇
  1972年   1篇
  1971年   14篇
  1967年   1篇
排序方式: 共有2232条查询结果,搜索用时 31 毫秒
261.
/ Data from historical aerial photographs analyzed with a GIS show that river channel change on the Salt River in the Phoenix metropolitan area of central Arizona has been driven by large-scale regional flood events and local human activities. Mapping of functional surfaces such as low-flow channels, high-flow channels, islands, bars attached to channel banks, and engineered surfaces shows that during the period from 1935 to 1997, the relative areal coverage of these surfaces has changed. Flood events have caused general changes in sinuosity of the low-flow channel, but islands have remained remarkably consistent in location and size, while channel-side bars have waxed and waned. The most important determinant of local channel form and process is sand and gravel mining, which in some reaches occupies more than 70% of the active channel area. The general location of mining is closely related to the location of the moving urban fringe, which serves as a market for sand and gravel during construction. Quantitative spatial analysis of imagery supplemented by field mapping shows that for each location within the general channel area, it is possible to specify a probability of encountering a low-flow channel or other fluvial features. Maps showing the distribution of these probabilities of occurrence reveal the most probable location and configuration of the channel as it occurred in the past. Some reaches have the low-flow channel located persistently within a limited area as a result of bedrock or sinuosity controls, but other reaches dominated by flow separation or shallow gradient have almost no persistence in channel location from one flood to another.  相似文献   
262.
/ The necessity to tailor information becomes increasingly urgent as the information revolution continues to generate ever-increasing flows of data and so-called information. From European experiences, a new approach for monitoring system design is suggested in this paper. In this approach, careful and detailed specification of information needs is a major contributing factor to the effectiveness of information products. To develop better specifications for information products, the process of collecting and transforming data into useful information requires careful thought and guidance. A dialogue between information users on one hand and information producers on the other is essential. This dialogue can be based on the information cycle, describing the continuous process from specifying information needs for water management and a strategy to collect information through data collection and data analysis up to utilization of information by water management. By following the respective steps in the information cycle, the process of information gathering can be completed. The cyclic character provides a quantitative means of connecting monitoring system design and operations with the information expectations and/or products required by management.  相似文献   
263.
Satellite imagery is a useful tool for large-scale habitat analysis; however, its limitations need to be tested. We tested these limitations by varying the methods of a habitat evaluation for white-tailed deer (Odocoileus virginianus) in the Adirondack Park, New York, USA, utilizing harvest data to create and validate the assessment models. We used two classified images, one with a large minimum mapping unit but high accuracy and one with no minimum mapping unit but slightly lower accuracy, to test the sensitivity of the evaluation to these differences. We tested the utility of two methods of assessment, habitat suitability index modeling, and pattern recognition modeling. We varied the scale at which the models were applied by using five separate sizes of analysis windows. Results showed that the presence of a large minimum mapping unit eliminates important details of the habitat. Window size is relatively unimportant if the data are averaged to a large resolution (i.e., township), but if the data are used at the smaller resolution, then the window size is an important consideration. In the Adirondacks, the proportion of hardwood and softwood in an area is most important to the spatial dynamics of deer populations. The low occurrence of open area in all parts of the park either limits the effect of this cover type on the population or limits our ability to detect the effect. The arrangement and interspersion of cover types were not significant to deer populations.  相似文献   
264.
/ The success of the Toxics Release Inventory (TRI) stands in stark contrast to most other environmental regulations in the United States. Between its inception in 1988 and 1995, releases of chemicals listed on the TRI have declined by 45%. We argue the TRI has achieved this regulatory success by creating a mechanism of "populist maxi-min regulation." This style of regulation differs from traditional command-and-control in several ways. First, the majorrole of public agencies is not to set and enforce standards, but to establish an information-rich context for private citizens, interest groups, and firms to solve environmental problems. Second, environmental "standards" are not determined by expert analysis of acceptable risk, but are effectively set at the levels informed citizens will accept. Third, firms adopt pollution prevention and abatement measures in response to a dynamic range of public pressures rather than to formalized agency standards or governmental sanction. Finally, public pressure ruthlessly focuses on the worst polluters-maximum attention to minimum performers-to induce them to adopt more effective environmental practices. TRI has inadvertently set in motion this alternative style of regulation that has, in turn, dramatically reduced toxics emissions in the United States. By properly understanding the mechanisms that drive TRI's accomplishments, more intentional public policy designs can expand the system of populist maxi-min regulation and achieve even more rapid toxics reduction.  相似文献   
265.
2 semiarid irrigated area with salt-affected soils. The available soil map is at 1:100,000 scale and its mapping units are used for the land evaluation with the FAO framework. These data are then elaborated using the index value method. This procedure gives a map of land evaluation units and a table that rates the productive potential of these units for six crops: alfalfa, barley, maize, rice, sunflower, and wheat.  相似文献   
266.
The objective of this study was to investigate the impact of tourism activities on olive tree cultivation and the human population of the island of Lesbos. The presence or absence of tourism is related with the maintenance or abandonment of olive tree cultivation and population changes for each community. A spatial segregation of the island is evident, related to tourist development, olive tree cultivation, and population change. The results of the study demonstrate that in communities where tourism plays an important role olive tree cultivation is preserved and the population is stable. The preservation of the agro-ecosystem is assured while the olive groves remain productive. Simultaneously, the landscape, which provides specific attractions for tourism, is not altered.  相似文献   
267.
/ Implementing the concept of sustainability through integrated approaches to natural resource management poses enormous challenges for both the rural communities and government agencies concerned. This paper reviews the underlying rhetoric of sustainable agricultural systems and the integrated resource management paradigm and identifies some of the challenges being experienced in translating this rhetoric into practice. A relatively recently implemented community-based integrated catchment management (ICM) process in a rural community in northeast Australia is examined in terms of some of the lessons learned that may be relevant to other similar integrated resource management (IRM) processes. It reveals a pragmatic, opportunistic, and evolving implementation process based on adaptive learning rather than a more traditional "rational" planning approach. Some essential characteristics of a community-based IRM process are identified, including fostering communication; providing a structure that fosters cooperation and facilities coordination among community, industry, and government agencies; the integration of IRM principles into local government planning schemes; and an emergent strategic approach to IRM program implementation. We conclude by identifying some essential characteristics of an IRM process that can assist a community to adapt to, and manage change for, sustainable resource use.  相似文献   
268.
文章分析了浙江省在废纸再生方面的3个典型模式的经验,指出了存在的问题并提出了建议对策。  相似文献   
269.
介绍瓦斯传感器的国内外研究现状,给出以设备网(DeviceNet)总线构成的瓦斯传感器检测网络结构。简要分析了DeviceNet总线协议特点以及其关键技术,提出具有DeviceNet总线规范的矿井瓦斯传感器的设计及实现方案。硬件电路主要由信号调理电路、数字信号处理器,以及能实现DeviceNet网络通信的接口电路构成,用对象建模的方法构建了矿井瓦斯传感器的对象模型,并用模块化编程技术实现了矿井瓦斯传感器作为一个网络从设备的应用层的软件设计。该传感器作为从设备和带有PCI-CAN网卡的计算机组成主/从连接网络,能对多个矿井瓦斯传感器的数据实现远距离的控制。  相似文献   
270.
ABSTRACT: Landsat radiance values were processed at two different (single and double) levels of accuracy to estimate chlorophyll a, turbidity, and suspended sediment in Lake Okeechobee, Florida. Both ordinary least square and ridge regression analyses were used to establish a relationship between water quality parameters and Landsat radiance. Radiance measurements made at greater precision (double level) gave a better solution in this application. The ridge regression analysis for double level not only can reduce the total mean square error about 13–20 percent and confidence interval about 6–28 percent as compared to ordinary least square analysis, but it can also change the interpretation of analysis results.  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