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   32896篇
  免费   363篇
  国内免费   263篇
安全科学   1067篇
废物处理   1660篇
环保管理   4175篇
综合类   4837篇
基础理论   8371篇
环境理论   14篇
污染及防治   8522篇
评价与监测   2421篇
社会与环境   2261篇
灾害及防治   194篇
  2023年   172篇
  2022年   358篇
  2021年   450篇
  2020年   249篇
  2019年   310篇
  2018年   567篇
  2017年   597篇
  2016年   902篇
  2015年   613篇
  2014年   1026篇
  2013年   2767篇
  2012年   1241篇
  2011年   1600篇
  2010年   1282篇
  2009年   1270篇
  2008年   1572篇
  2007年   1520篇
  2006年   1341篇
  2005年   1194篇
  2004年   1125篇
  2003年   1056篇
  2002年   1000篇
  2001年   1126篇
  2000年   796篇
  1999年   503篇
  1998年   378篇
  1997年   389篇
  1996年   403篇
  1995年   480篇
  1994年   402篇
  1993年   345篇
  1992年   380篇
  1991年   357篇
  1990年   329篇
  1989年   322篇
  1988年   297篇
  1987年   242篇
  1986年   249篇
  1985年   248篇
  1984年   267篇
  1983年   254篇
  1982年   269篇
  1981年   221篇
  1980年   166篇
  1979年   182篇
  1978年   164篇
  1977年   133篇
  1975年   137篇
  1973年   167篇
  1972年   142篇
排序方式: 共有10000条查询结果,搜索用时 875 毫秒
91.
Classification and distribution of mangrove vegetation are vital information for the proper development of a mangrove management plan. In this study, classification for the mangroves of the district of Kemaman were done using both 1 : 5000 aerial photographs and Landsat TM imageries. The coverage by aerial photographs is limited to the coastal and estuarine areas only. Thus, for areas further upstream of the aerial photo coverage, Landsat TM imageries were used. Analysis of aerial photographs and remote sensing images revealed that the mangroves of Kemaman could be classified into 14 different classes of vegetation. All the 14 classes were identified from areas covered by the aerial photographs. For areas covered by the Landsat images only 7 classes of vegetation were identified. The accuracy for aerial photograph and Landsat images are 91.2% and 87.8%, respectively. It can be concluded that although both techniques are useful in determining the mangrove vegetation classes, the large 1 : 5000 aerial photographs are more accurate and provided more detailed information comparatively.  相似文献   
92.
The effect of mountain relief and industrial air pollution on biometric parameters of pine stands was studied. The empirical–statistical models of the dependence of biometric characteristics on the parameters of forest sites were developed using raster modeling and multivariate analysis. The possibility of predicting changes in the biometric parameters at any site on the basis of these models is shown.  相似文献   
93.
In recent years flows of foreign direct investment (FDI) to developing countries have rapidly been increasing. It is now an important contributor to the national economy and urban growth in scores of developing countries. Rapid urbanization in these countries is leading to many problems in the cities. Existing urban infrastructure and municipal services have been unable to cope with the increased demand arising from growing population and rapid economic growth. Consequently, the environment in these cities has deteriorated alarmingly. This paper assesses the role of FDI in urban environmental management (UEM) by analyzing the linkages between them for Hanoi City in Vietnam. The paper's analysis and findings are presented under three main themes: one, FDI, employment and income; two, FDI and environmental degradation; and three, potential of utilizing FDI for the provision of urban environmental infrastructure and services (UEI&S) in order to improve the urban environment. Both primary and secondary source data have been used. Policy implications of the research findings are drawn from the perspective of sustainable development.  相似文献   
94.
95.
Assessment of environmental changes in the Orinoco River delta   总被引:1,自引:0,他引:1  
Major anthropogenic driven changes in the hydrologic and sedimentation patterns of the Orinoco River have had an impact on environmental conditions in the delta. The abrupt water flow reduction from 3,600 to 200 m3 s–1 in one of its major distributaries resulting from dam construction forced its transformation from a fresh-water body into a tidal channel with an increase in salinity level (as far as 100 km upstream) and with well-mixed water at the mouth and estuarine connection to the Paria Gulf. Three different sectors along this distributary can be identified (indicated by the Na/Cl ratio in the water). As a result, noticeable changes have occurred in the mangrove community which moved about 60 km further upstream. The changes have also promoted the formation of new islands of sediment progradation at the mouth of this distributary, where successional colonization and species replacement by different species of grasses and mangroves take place. Electronic Publication  相似文献   
96.
We present a case of ultrasonographic prenatal diagnosis at 24 weeks of femur—fibula—ulna (FFU) complex. To our knowledge, this is the first report of an early prenatal diagnosis of FFU.  相似文献   
97.
98.
Observations of air temperature changes in a steppe marmot burrow were performed from late July to mid-October. Until early September, temperature in the burrow remained relatively constant, but then it began to decrease rapidly. This occurred after air temperature above the ground became equal to the temperature in the burrow. Supposedly, it is in this particular period that marmots begin to plug the entrance to the burrow with earth, thus reducing heat exchange between the increasingly cold aboveground air and the air in the burrow.  相似文献   
99.
In the periods of summer and autumn bloom of the Stephanodiscus hantzschii Crun. in recreational water bodies, studies on the vertical distribution of chlorophyll a, its contents per unit biomass, efficiency in using photosynthetically active radiation (EPhAR), and assimilative activity of microalgae were performed. The results confirmed the existence of two ecophysiological forms of St. hantzschii and provided evidence that both forms are typically autotrophic and can efficiently use low-intensity PhAR for photosynthesis.  相似文献   
100.
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