全文获取类型
收费全文 | 640篇 |
免费 | 76篇 |
国内免费 | 436篇 |
专业分类
安全科学 | 21篇 |
废物处理 | 33篇 |
环保管理 | 47篇 |
综合类 | 643篇 |
基础理论 | 189篇 |
环境理论 | 1篇 |
污染及防治 | 185篇 |
评价与监测 | 19篇 |
社会与环境 | 12篇 |
灾害及防治 | 2篇 |
出版年
2024年 | 2篇 |
2023年 | 18篇 |
2022年 | 36篇 |
2021年 | 37篇 |
2020年 | 28篇 |
2019年 | 37篇 |
2018年 | 40篇 |
2017年 | 41篇 |
2016年 | 54篇 |
2015年 | 47篇 |
2014年 | 70篇 |
2013年 | 62篇 |
2012年 | 74篇 |
2011年 | 88篇 |
2010年 | 59篇 |
2009年 | 62篇 |
2008年 | 50篇 |
2007年 | 43篇 |
2006年 | 54篇 |
2005年 | 36篇 |
2004年 | 42篇 |
2003年 | 30篇 |
2002年 | 19篇 |
2001年 | 32篇 |
2000年 | 26篇 |
1999年 | 15篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1978年 | 1篇 |
排序方式: 共有1152条查询结果,搜索用时 15 毫秒
961.
Coltan from Central Africa,international trade and implications for any certification 总被引:1,自引:0,他引:1
The exploitation of coltan in Central Africa can be considered a case of conflict minerals due to its nature. Many international organizations and bodies, national governments and private sector organizations seek to address this conflict, in particular via transparency, certification and accountability along the material supply chain. This paper analyses the international trade dimension of coltan and gives evidence on the dimension of illicit trade of coltan. The authors start from the hypothesis that illicit trade of coltan sooner or later will enter the market and will be reflected in the statistics. The paper is structured in the following manner: first, a short section gives a profile of coltan production and markets; second, an overview of the mining situation in the Democratic Republic of Congo (DRC) and related actors. The third section addresses mechanisms, actors and measurement issues involved in the international trade of coltan. The final part draws lessons for certification and conflict analysis and offers some guidance for future research. 相似文献
962.
R. Riffaldi M. Filippelli R. Levi‐Minzi A. Saviozzi 《Journal of environmental science and health. Part. B》2013,48(4):455-465
Abstract A laboratory experiment was performed in order to evaluate the extent to which metam sodium (MS) applied at two different recommended rates and its degradation product, methyl isothiocyanate ( MITC ), affect soil respiration. Results suggest that MS degradation to MITC was complete within 4 hours and that MITC decomposed quickly in a few days, except in the soil containing high organic matter where it was still present after 15 days. Following the addition of MS, a lag phase appeared in CO2‐C evolution in the soil. It was longer for the higher dose of MS added and for the two soils with low organic C content. The dynamics of the process was described by the Bonde and Rosswall model and by the Gompertz RS E model for the untreated and the MS‐treated soils, respectively. 相似文献
963.
基于SWAT与DNDC模型对比研究亚热带流域氮淋溶与输出过程 总被引:2,自引:2,他引:2
本研究通过对亚热带香溪河小流域的氮输出进行长期监测,并通过DNDC与SWAT模型对流域氮素流失进行对比模拟研究,以期为合理建立适合亚热带流域氮循环模型提供科学依据.结果表明:(1)影响DNDC模型模拟小流域内氮素流失的关键参数包括降水、坡度以及氮肥施用量,而影响SWAT模型模拟的关键参数包括地下水滞后系数、最大冠层截留量、基流系数和土壤蒸发补偿系数;(2)DNDC模型模拟小流域内2014年的径流量、TN和NO-3-N排放量与实测值的偏差分别为5.19%、8.10%和71.70%,SWAT模型模拟小流域内2014年的TN、NO_3~--N和NH_4~+-N的排放量与实测值的偏差分别为2.04%、14.29%和8.89%;(3)通过对SWAT与DNDC模拟结果对比分析香溪小流域氮素流失时空分布特征,进一步耦合了DNDC和SWAT模型,有助于提高亚热带流域氮素流失模拟精确度. 相似文献
964.
深圳市土地利用变化驱动力系统分析 总被引:13,自引:0,他引:13
以深圳市土地利用变化的驱动力系统为例,用灰色关联方法确定影响土地利用变化的驱动因子并判别其最大驱动力,结果表明:深圳城市建设用地面积变化与外资利用额的关联系数最大,达到0.8491,其次为基础建设投资颧、第三产业产值、工业总产值及总人口数量;耕地、林地、荒地、水域面积变化则与城市化率的关联系数最大。以1991-1999年间的建设用地面积作为灰色系统特征数据序列,选取与其关联系数最大的五个驱动因子序列数据作为相关因素数据系列,建立CM(1,6)模型,结果表明:该模型的计算值和实际值的相对误差最大为11.11%,最小为-0.25%,平均相对误差也只有3.41%;检验结果表明,2000-2004年的模拟值与检验值的平均相对误差仅为3.74%,模拟精度较高,因而可以利用该模型预测深圳市建设用地的增长规模。 相似文献
965.
Swati Mookherji Gregory W. McCarty Jonathan T. Angier 《Journal of the American Water Resources Association》2003,39(2):381-387
ABSTRACT: Dissolved gas analysis permits direct detection of ground water denitrification, a technique we used in this study to assess the fate of nitrate in a riparian wetland. Dissolved argon (Ar) and dinitrogen (N2) were measured in transects of nested piezometers installed at different depths within upwelling regions of a riparian wetland. The method uses the Ar content in the water as a natural inert tracer for assessing background content of N2 from the previous air/water equilibrium. Within the wetland under study, anoxic to suboxic ground water became more oxic in piezometers close to the aquifer layer, indicating upwelling of oxic ground water. Assessment of loss of nitrate and Ar in ground water within an upwelling zone indicated that shallow piezometers had significant N2 loss through degassing. Most of the measured nitrate‐nitrogen (NO3?‐N) loss of 205 μM in a piezometer nest could be accounted for by total N2‐N produced (169 μM N), calculated from changes in dissolved N2 and estimated N2 degassed. Degassing due to methane (CH4) production was also detected in some shallow piezometers within nests. This technique for analysis of dissolved gases in ground water can be applied to detect small changes in N gas concentration and aids in assessing the fate of nitrate along a ground water flow path. 相似文献
966.
以碳化稻壳为组分原料,添加氮化硅和少量烧结助剂,在1 500℃到1 550℃下成功一步合成制备出多孔β-Si3N4陶瓷。采用Archimedes法、三点弯曲法测量了烧结试样的密度,显气孔率及抗弯强度。通过XRD测定了烧结试样的物相组成,并用SEM观察了试样的显微形貌。结果表明,从1 450~1 550℃时,试样的显气孔率从33.76%降低至30.68%,其弯曲强度从62.78 MPa增加到76.64 MPa。1 500℃烧结试样中,β-Si3N4晶粒长径比约为10,β-Si3N4晶粒间孔的分布均匀,孔径尺寸约为2 μm。 相似文献
967.
利用成熟硫化物自养反硝化活性污泥,采用微电极系统探讨初始S/N比率对N2O还原与积累释放的影响。研究结果表明,在硫化物自养脱氮过程中,提高初始S/N有效缓解了不同氮还原酶之间的电子竞争,不仅明显提高了N2O与NO3-的降解速度,而且能避免了NO2-、FNA以及N2O的积累。其中,N2O的积累量与FNA的积累量正相关且变化倍数接近,表明FNA的存在可能会明显抑制N2O还原酶活性;而硫化物在一定范围内提高浓度,不仅不会对硫化物自养反硝化脱氮过程产生抑制,反而会促进自养反硝化过程的进行,降低N2O的积累释放。 相似文献
968.
Yang Yang Xiuzhen Zheng Wei Ren Jiafang Liu Xianliang Fu Sugang Meng Shifu Chen Chun Cai 《Frontiers of Environmental Science & Engineering》2022,16(11):137
969.
15N-labeling and solid-state 13C and 15N nuclear magnetic resonance (NMR) spectroscopy was applied to study the immobilization of 2,4,6 trinitrotoluene (TNT) into
soil organic matter (SOM). Uncontaminated soil from the Ap horizon of a Luvisol was mixed with 15N-TNT (enrichment: 99 atm%) and laid over an unspiked layer of the same material. The latter covered soil from the Bt horizon.
The microcosms were aerobically incubated under laboratory conditions for up to 11 months. After 1 week, within the total
microcosm approximately 90% of the added 15N (15Nadd) were recovered, mostly in the top layer (87%). After 11 months, this amount decreased to 71%, indicating losses due to denitration
or transamination. Within two months, half of 15Nadd had been immobilized in the residues not extractable with organic solvents and water. The amount of the sequestered 15Nadd remained fairly constant until the end of the experiment pointing towards a high stability of TNT-SOM associates. Solid-state
15N NMR revealed their formation by covalent binding, most tentatively as amides. Complete reduction of TNT to triaminotoluene
(TAT) was not prerequisite. The most pronounced downwards movement of 15N-TNT occurred during the first two months. The major part of it, however, experienced quick immobilization, leaving approximately
10% of 15Nadd recovered in the leachate at the end of the experiment. Calculations indicated contributions of inorganic 15Nadd. Approximately 25% of its organic 15Nadd originated from condensed N, suggesting that in soils the transport of partly reduced TNT is in close association with the
organic matter of the soil solution to which they are covalently bound. 相似文献
970.
N‐acetyltransferase (NAT) activity was determined in different ages of New Zealand White rabbit pineal gland using 2‐aminofluorene and p‐aminobenzoic acid as substrates and it was assayed by high pressure liquid chromatography. Rabbits of different ages were either sacrificed during the light phase, exposed to darkness or light for 1 min during the dark phase of the lighting cycle, returned to their cages in darkness for 30 min and then sacrificed. Pineal gland NAT activity in animal nocturnally exposed to 1 min of light was inhibited in animals 1 ‐day‐old of age. Nocturnal light exposure did not inhibit enzyme activity in 1‐day‐old rabbit, even though these animal displayed clear light : dark differences in pineal gland NAT activity. Nocturnal light exposure also did not inhibit night time levels of NAT activity in 1‐day‐old animals who had been bilaterally enucleated. The result suggested that this effect is retinally mediated. Pre‐treatment of 1‐day‐old and 60‐day‐old animals with the isoproterenol (beta‐noradrenoreceptor agonist drug), prevented the nocturnal light‐induced inhibition of NAT activity. The different sensitivity of 60‐day‐old and 1‐day‐old animals to different illuminances or durations of nocturnal light exposure, was that the duration or intensity of light exposure was enable to inhibit nocturnal NAT activity. The NAT activity was at least 3.2‐ to 4.6‐fold greater in 1‐day‐old rabbits compared to 60‐day‐old rabbits. Kinetic constants for arylamine NAT activity in pineal gland from rabbits were determined. Km and Fmax values for 2‐aminofluorene were 2.6‐fold higher for light exposure than for no light exposure rabbits. This is the first demonstration of the retina‐pineal gland pathway appears light‐induced changes in pineal glands of animals in 1‐day‐old of ages or older; but this pathway does not function in 60‐day‐old rabbits like manner in 1‐day‐old rabbits. 相似文献