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   41100篇
  免费   475篇
  国内免费   357篇
安全科学   1351篇
废物处理   1865篇
环保管理   5653篇
综合类   6713篇
基础理论   10654篇
环境理论   18篇
污染及防治   10033篇
评价与监测   2767篇
社会与环境   2585篇
灾害及防治   293篇
  2022年   334篇
  2021年   394篇
  2020年   271篇
  2019年   336篇
  2018年   563篇
  2017年   624篇
  2016年   948篇
  2015年   720篇
  2014年   1071篇
  2013年   3431篇
  2012年   1336篇
  2011年   1778篇
  2010年   1426篇
  2009年   1524篇
  2008年   1824篇
  2007年   1792篇
  2006年   1628篇
  2005年   1405篇
  2004年   1364篇
  2003年   1313篇
  2002年   1211篇
  2001年   1461篇
  2000年   1061篇
  1999年   660篇
  1998年   516篇
  1997年   508篇
  1996年   553篇
  1995年   629篇
  1994年   543篇
  1993年   503篇
  1992年   536篇
  1991年   507篇
  1990年   485篇
  1989年   454篇
  1988年   414篇
  1987年   348篇
  1986年   359篇
  1985年   379篇
  1984年   393篇
  1983年   392篇
  1982年   398篇
  1981年   354篇
  1980年   288篇
  1979年   311篇
  1978年   249篇
  1977年   230篇
  1975年   200篇
  1974年   214篇
  1973年   239篇
  1972年   226篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
81.
A number of Mn-oxide minerals in soils from a farm in North Devon have been tentatively identified using a combination of advanced analytical techniques: scanning electron microscopy (SEM), scanning electron microprobe (SEMP), X-ray diffraction (XRD) and bulk chemical analysis by wet digestion followed by inductively-coupled plasma spectrometry (ICP). The minerals lithiophorite and hollandite are thought to occur throughout the study area although there is considerable geographical variation in the proportions of minerals present. Bimessite, vernadite, romanechite, todorokite and cryptomelane may also be present, although in smaller amounts. The use of SEMP, together with a simple sorption experiment, has allowed a study of the extent of uptake of Co and Cu by different Mn-oxide minerals. Lithiophorite appears to take up Co and Cu more effectively than hollandite within a pH range of 4–6.  相似文献   
82.
83.
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   
84.
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   
85.
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   
86.
87.
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   
88.
89.
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   
90.
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   
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