全文获取类型
收费全文 | 19135篇 |
免费 | 366篇 |
国内免费 | 3810篇 |
专业分类
安全科学 | 734篇 |
废物处理 | 1384篇 |
环保管理 | 2047篇 |
综合类 | 6006篇 |
基础理论 | 4658篇 |
环境理论 | 2篇 |
污染及防治 | 5521篇 |
评价与监测 | 1357篇 |
社会与环境 | 1206篇 |
灾害及防治 | 396篇 |
出版年
2024年 | 5篇 |
2023年 | 151篇 |
2022年 | 481篇 |
2021年 | 389篇 |
2020年 | 282篇 |
2019年 | 266篇 |
2018年 | 1779篇 |
2017年 | 1766篇 |
2016年 | 1673篇 |
2015年 | 789篇 |
2014年 | 822篇 |
2013年 | 1053篇 |
2012年 | 1346篇 |
2011年 | 2198篇 |
2010年 | 1353篇 |
2009年 | 1245篇 |
2008年 | 1601篇 |
2007年 | 1789篇 |
2006年 | 496篇 |
2005年 | 384篇 |
2004年 | 318篇 |
2003年 | 413篇 |
2002年 | 401篇 |
2001年 | 266篇 |
2000年 | 270篇 |
1999年 | 246篇 |
1998年 | 257篇 |
1997年 | 242篇 |
1996年 | 222篇 |
1995年 | 173篇 |
1994年 | 118篇 |
1993年 | 122篇 |
1992年 | 104篇 |
1991年 | 79篇 |
1990年 | 54篇 |
1989年 | 26篇 |
1988年 | 27篇 |
1987年 | 10篇 |
1986年 | 17篇 |
1985年 | 12篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1935年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 431 毫秒
991.
氮掺杂氧化钛的简易制备及可见光催化活性的研究 总被引:1,自引:1,他引:0
为开发对可见光响应的催化剂,以尿素为氮掺杂剂,采用简易溶胶-凝胶法制备氮掺杂氧化钛,并以2,4-DCP的降解检验其光催化活性。XRD、BET、XPS和UV-Vis漫反射光谱分析表明,随着氮/钛原子比(N/Ti)的增大,各催化剂晶粒尺寸减小,比表面积增大,锐钛矿相向金红石相的转变得到抑制,除0#样品出现金红石相外,其他催化剂均只出现锐钛矿相;掺入催化剂的N位于晶格O位点和晶格间隙,替代N和间隙N掺杂使催化剂的光吸收发生明显的红移。荧光光谱分析表明,当N/Ti在0~6范围内增加时,反应体系中·OH自由基的产生速率增加,当N/Ti增大至8时,速率则下降。相似的规律也表现在氮掺杂量对光催化活性的影响。适量氮掺杂能增强氧化钛的可见光催化活性,该改性催化剂可用于有机污染物的太阳光激催化降解。 相似文献
992.
超细粉煤灰基成型吸附剂的动态吸附实验 总被引:2,自引:1,他引:1
以粉煤灰为原料制备成型吸附剂,对水溶液中亚甲基蓝和Cr6+进行动态吸附研究,绘制穿透曲线,利用Origin软件对实验数据分析处理,得出穿透曲线的通式Ct=A1-A2〖〗1+(t/t0)p+A1。结果表明,初始浓度C0=25 mg/L,填料高度不同时,达到穿透点的时间随填料高度的增加而增加;填料高度h=200 mm,初始浓度不同时,达到穿透点的时间随初始浓度的增加而减小;该吸附剂对有机染料和重金属离子均有较好的吸附性能;穿透曲线通式的回归线性相关系数表明,该通式可很好地反映超细粉煤灰成型吸附剂的动态吸附过程。 相似文献
993.
厌氧序批式反应器内挥发性脂肪酸积累特性研究 总被引:1,自引:0,他引:1
小试规模的厌氧序批式反应器(ASBR),通过人工配水,研究了启动3个月时间以及一个运行周期内反应器内挥发性脂肪酸(VFA)的积累情况,并通过分析期间产甲烷活性的变化说明了控制VFA积累的重要性。经过近120 d的运行,乙酸和丙酸的最大比产甲烷活性分别提高了1.8和2.2倍,说明反应器的启动过程即是微生物群落的优化和选择的过程,ASBR的抗冲击的能力较强说明随启动的进行和种群的优化,活性污泥凝聚性能增强,对VFA的降解能力增强。 相似文献
994.
Epidemiological studies suggesting the possibility of harmful effects on human (specifically children’s leukaemia) due to
long-term exposure to magnetic fields of extremely low frequency (e.g. 50/60 Hz) and relatively low values (i.e. over the
microtesla range) have stirred high activity in the topic of magnetic field mitigation. To reduce these fields, it is common
to use passive metal screens (e.g. plates made of aluminium or steel). To design them, effective and fast numerical computations
are highly desirable. In this article, a method is presented, which computes various parameters of screens in a given shielding
problem and yields magnetic field distribution and shielding factors. The method takes into consideration the 3D field distribution
and is able to solve systems with large aspect ratios (thin thickness in comparison with its other dimensions); this is a
common problem where other methods such as finite elements often experience difficulties. The presented method computes separately
the field inside and outside the screens. Afterwards, the solutions are “stitched” together along the border of the subregions.
Two practical examples are given of the developed numerical method. 相似文献
995.
On experimental setup in bioelectromagnetics 总被引:1,自引:1,他引:0
Bioeffects created by electromagnetic field (EMF) are the subject of intensive studies. This paper critically considers estimations
of exposure to EMF in bioelectromagnetic experiments. Results of calculations presented herein show the significant role of
the presence of conducting bodies (the exposure system) near an object under test on EMF energy absorption as well as mutual
interactions between simultaneously exposed objects. Our aims herein are twofold: firstly to find a way to refer measurement
results to free-space conditions in order to enable comparison of results obtained in different laboratories, and secondly
to show that EMF energy absorption in any exposed object is different and that this difference is a function of the size of
the exposure system, the number of exposed objects, and the particular properties (i.e., the electromagnetic structure) of
the objects. In the authors’ opinion the existence of interactions caused by the presence of the exposure system and other
exposed objects is a reason why remarkable differences are observed between experiments performed even under supposedly identical
conditions. The presented considerations and conclusion suggest wider participation of physicists and engineers in bioelectromagnetic
experiments in order to ensure the correctness of metrological aspects of these experiments. 相似文献
996.
Urbanization and its impact on groundwater: a remote sensing and GIS-based assessment approach 总被引:1,自引:0,他引:1
The perils of unplanned urbanization and increasing pressure of human activities on hydro-geomorphologic system often result
in modification of the existing recharge mechanism, which leads to many environmental consequences. In the present research,
an attempt has been made to investigate the applicability of remote sensing and geographical information system (GIS) in dealing
with spatial and temporal variability of dynamic phenomena, like urbanization and its impact on groundwater. This paper covers
primarily, quantitative and qualitative impacts of urban growth on the behavior of aquifer in Ajmer city (India). Urban growth
of the Ajmer city in last 17 years has been estimated from the satellite images. Database related to urbanization and groundwater
has been created in GIS. Groundwater recharge has been computed using a water balance approach known as Water Level Fluctuation
Methodology. Recharge estimation methodology has been implemented in GIS to introduce the spatial variability of hydro-geological
characteristics. Further, temporal and spatial variations in groundwater quality and quantity have been correlated with urban
growth using overlay analysis in GIS. The study reveals a general decline in water table and quality with urbanization. Further,
remote sensing and GIS technologies have been found useful in assessment of spatial and temporal phenomena of urbanization
and its impact on groundwater system. 相似文献
997.
998.
999.
1000.
针对城市化进程加快引发的一系列环境污染问题,指出了加快污染防治设施社会化运营的必要性,并从污染治理设施的种类、污染治理设施的社会化运营分析和运作模式三方面论述了如何进行污染治理设施的社会化运营,从经济发展、污染防治设施运行、引入竞争机制等方面概述了污染防治设施社会化运营对区域环境与经济协调发展的影响。 相似文献