全文获取类型
收费全文 | 3430篇 |
免费 | 320篇 |
国内免费 | 578篇 |
专业分类
安全科学 | 512篇 |
废物处理 | 35篇 |
环保管理 | 458篇 |
综合类 | 1848篇 |
基础理论 | 477篇 |
污染及防治 | 138篇 |
评价与监测 | 275篇 |
社会与环境 | 343篇 |
灾害及防治 | 242篇 |
出版年
2024年 | 11篇 |
2023年 | 74篇 |
2022年 | 92篇 |
2021年 | 137篇 |
2020年 | 114篇 |
2019年 | 122篇 |
2018年 | 105篇 |
2017年 | 161篇 |
2016年 | 183篇 |
2015年 | 179篇 |
2014年 | 180篇 |
2013年 | 247篇 |
2012年 | 349篇 |
2011年 | 334篇 |
2010年 | 242篇 |
2009年 | 211篇 |
2008年 | 174篇 |
2007年 | 227篇 |
2006年 | 217篇 |
2005年 | 170篇 |
2004年 | 110篇 |
2003年 | 97篇 |
2002年 | 87篇 |
2001年 | 67篇 |
2000年 | 76篇 |
1999年 | 56篇 |
1998年 | 39篇 |
1997年 | 43篇 |
1996年 | 34篇 |
1995年 | 26篇 |
1994年 | 37篇 |
1993年 | 32篇 |
1992年 | 18篇 |
1991年 | 21篇 |
1990年 | 16篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有4328条查询结果,搜索用时 312 毫秒
281.
Natural circulation driven boiling systems are extensively used for passive heat removal, such as in nuclear power plants. The flashing phenomenon and the associated flow instabilities in a natural circulation loop are reported here. An experimental facility is constructed with a heater, an adiabatic riser, a condenser and an adiabatic down comer to study the instability regions. The experimental geometry is modeled using RELAP5. At high power (i.e., at 6 kW) flashing instability is observed when the inlet sub cooling is within the range of 7° C to 12° C. It is also found that the presence of an inlet restriction does not help to suppress the flashing induced flow oscillation. A good comparison between the experimental and numerical results is observed and this loop can be used for validation exercises of commercial codes. 相似文献
282.
本文应用四川省气象局提供的气候资料,借助于电子计算机,统计分析了太阳黑子位相与四川盆地热量资源、降水资源波动的关系;采用文献[2]的公式,计算了太阳黑子相对数年均值与热量、降水资源的同期及延后相关系数,并进行了周期分析,进而分析其演变趋势及其对农业生产的影响和应采取的对策。 相似文献
283.
The climate simulations from atmospheric general circulation models (GCMs) are often used to analyze the potential effects of climate change on environmental resources. It has been demonstrated that there are differences among the simulations from various GCMs, on spatial scales ranging from global to regional. This paper quantifies the differences in temperature and precipitation simulated by three major GCMs for four specific regions: an agricultural region (the North American winter wheat belt), a hydrologic region (the Great Basin), a demographic region (the high-density population corridor of the northeast United States), and a political region (the state of Texas). Both the current (control) climate and the climatic response to a doubling of atmospheric carbon dioxide (CO2) are consideredIn each region, even when the data are averaged on a seasonal basis, marked differences occurred in the areal average climate simulated by the different GCMs for both the control climate and the doubled-CO2 climate. Thus, climate impact studies based on the simulations of more than one GCM could easily yield a range of possible results 相似文献
284.
Sensitivity indices, which rank factors pertinent to surface and subsurface runoff pathways, were used to identify phosphorus
source areas in riparian zones of 15 northern Minnesota lakes. Watershed models were first developed using a geographic information
system (GIS). Empirical models were then developed correlating water quality with land use, lake morphometry, and riparian
sensitivity. Base models of forested, cultivated, pasture/open, wetland and residential land use within 100, 200, 400, and
2000 m of the study lakes were regressed on total phosphorus and chlorophyll-a. Area-weighted groundwater and surface runoff sensitivity indices were then incorporated into each model and tested for significance.
Within the 200-m buffer, the total phosphorus base model was improved by including the groundwater index alone. The chlorophyll-a base model at 200 m was improved by including: (1) the groundwater index alone, and (2) both the groundwater and surface
runoff sensitivity indices. Results suggest that surface and subsurface runoff analysis of potential source areas can improve
decision making for lake riparian management. 相似文献
285.
自然灾害灾情划分指标研究 总被引:6,自引:1,他引:6
本文阐述了灾情分析中的两个基本方面,即损失的规模和损失的深度,提出了灾级和灾度的概念,对于影响灾级和灾度的主要指标也进行了分析。并就时间和空间变化对灾级划分界线的影响作了论述。 相似文献
286.
287.
Nazzareno Diodato 《The Environmentalist》2006,26(1):63-70
Summary Seasonal rainerosivity is important in the structure and dynamics of Mediterranean ecosystems. The present paper contributes
to the quantitative assessment of RUSLE's monthly erosion index in a data-scarce Mediterranean region. Therefore, a regionalized
relationship for estimating monthly erosion index (EI30-month) from only three rainfall parameters has been obtained. Knowledge of the seasonal and annual distribution of erosivity index,
permit soil and water conservationists to make improved designs for erosion control, water harvesting or small hydraulic structures.
Although a few long data sets were used in the analysis, validation with established monthly erosivity index values from other
Italian locations, suggest that the model presented (r2 = 0.973) is robust. It is recommended to monthly erosivity estimates when experimental data-scarce rainfall become available. 相似文献
288.
289.
290.