全文获取类型
收费全文 | 12937篇 |
免费 | 4948篇 |
国内免费 | 27109篇 |
专业分类
安全科学 | 1505篇 |
废物处理 | 390篇 |
环保管理 | 1171篇 |
综合类 | 31048篇 |
基础理论 | 2723篇 |
环境理论 | 1篇 |
污染及防治 | 5752篇 |
评价与监测 | 1525篇 |
社会与环境 | 337篇 |
灾害及防治 | 542篇 |
出版年
2024年 | 17篇 |
2023年 | 117篇 |
2022年 | 274篇 |
2021年 | 300篇 |
2020年 | 885篇 |
2019年 | 2013篇 |
2018年 | 2154篇 |
2017年 | 2209篇 |
2016年 | 1903篇 |
2015年 | 2405篇 |
2014年 | 3044篇 |
2013年 | 3225篇 |
2012年 | 3186篇 |
2011年 | 2702篇 |
2010年 | 2488篇 |
2009年 | 2438篇 |
2008年 | 2067篇 |
2007年 | 2102篇 |
2006年 | 1532篇 |
2005年 | 1159篇 |
2004年 | 1047篇 |
2003年 | 818篇 |
2002年 | 683篇 |
2001年 | 707篇 |
2000年 | 802篇 |
1999年 | 685篇 |
1998年 | 524篇 |
1997年 | 496篇 |
1996年 | 510篇 |
1995年 | 452篇 |
1994年 | 284篇 |
1993年 | 222篇 |
1992年 | 291篇 |
1991年 | 270篇 |
1990年 | 230篇 |
1989年 | 205篇 |
1988年 | 146篇 |
1987年 | 72篇 |
1986年 | 74篇 |
1985年 | 54篇 |
1984年 | 59篇 |
1983年 | 40篇 |
1982年 | 45篇 |
1981年 | 34篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1961年 | 2篇 |
1932年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
Wan Soo Kim Seong Jin Yoon Jong Wook Kim Jung Ah Lee Tae Won Lee 《Marine Biology》2006,149(5):1209-1215
Diadromous fish often enter freshwater directly from seawater via fish ladders or channels built in estuarine dams. The oxygen consumption rates (OCR) of glass eel, Anguilla japonica, were determined using an automatic intermittent flow respirometer under various salinity and temperature regimes to physiologically explain this direct movement. The endogenous rhythm of the OCR in wild glass eels, freshly collected from estuaries, was nearly synchronous with the tidal pattern at the estuarine collection site. When the salinity was changed from 20 psu (12°C) at a constant temperature to that of freshwater, the OCR of the glass eels decreased by 21.6±7.0% (mean ± SD) (P<0.05), showing a dampened rhythm for about 48 h. After this period of impediment, the glass eels resumed normal metabolic activity. Direct migration from seawater to freshwater under constant temperature would result in a severe physiological stress for these glass eels for about two days. When the glass eels were exposed to a cyclic change in water temperature of 2°C 26 h−1, as they encounter in estuaries, and then were introduced to freshwater abruptly, the OCR rhythm corresponded to the cyclic changes in water temperature after exposure to freshwater. Under these conditions, the mean OCR of the glass eels had a small difference before and after exposure to freshwater. These data explained how glass eels can directly move from sea water into the freshwater without any apparent metabolic stress in the estuaries showing cyclic change in water temperature (Δt=2°C). 相似文献
43.
为了更好地发挥产氢产酸/同型产乙酸耦合系统在废水厌氧发酵生产乙酸方面的优势,有必要寻找一种简单有效的方法以获得该系统产酸的优化条件.利用经过加热处理并活化的厌氧污泥作种泥,以模拟废水中的葡萄糖为底物,针对发酵时间、底物浓度、种泥浓度、初始pH进行4因素10水平均匀设计实验,得到了乙酸生产指标与产酸条件之间关系的回归方程;也得到了以高乙酸产量为主要目标导向同时兼顾高乙酸产率和高乙酸生产强度目标的优化条件;优化条件实验乙酸浓度比均匀设计中最高乙酸浓度提高20%左右.研究表明,将均匀设计应用于废水产氢产酸/同型产乙酸耦合产酸条件优化,可以避免盲目性,迅速获得满意结果. 相似文献
44.
The Ernesto Tornquist nature reserve is a relict of native Pampas vegetation in Argentina. Alien trees were introduced to the reserve in the 1950s, mainly to "improve" the natural landscape, resulting in the arrival of a totally new life form. In 1987, a fire affected an area planted with Pinus halepensis resulting in its massive expansion. In 1999, we removed trees from 17 circular plots of 10 m diameter placed systematically within the area that was colonized after the fire. Trunks were cut 20 cm from the ground and growth rings were counted. We studied the age structure of the population in order to reconstruct the colonizing events after the fire. We found that recruitment occurred throughout this period, except in the three years after the disturbance. We suggest that this delay in recruitment might be caused by low seedling survival under water stress conditions due to low rainfall, combined with scarce vegetation cover after fire. This could have been associated with an initial reduction in propagule pressure due to the scarcity of surviving trees in the vicinity and with the fact that fire occurred after the peak of seed release, during an extremely dry summer, probably killing a great number of seeds that were already in the soil. In the following years, recruitment was probably aided by pioneer trees and later by seeds shed from established pines. Alien trees had been allowed to reach maturity due to wildfire prevention and control in the years preceding the fire and the accumulated dry matter resulted in increased fire intensity that reduced the ability of grasses to re-sprout. As a consequence, the invasion window that allowed the expansion of pines remained open for at least 12 years. 相似文献
45.
46.
优势菌的筛选及其强化活性污泥好氧反硝化的研究 总被引:1,自引:0,他引:1
利用含活性污泥提取物的贫培养基筛选SBR系统中的好氧异养优势菌。结合自然温度(15~20℃)、延长培养时间等条件来提高菌群的可培养性。从SBR活性污泥系统中分离出5种细菌。4株去除COD优势菌,1株异养硝化细菌,能在好氧条件下实现对总氮的去除。反应池底采用边缘对称曝气,反应池内细菌在时间顺序和空间位置上循环经历好氧过程及微氧过程。将PVA铝盐法固定的细菌对反应器进行生物强化。结果显示,在好氧工艺的条件下,投加优势菌群后,与未加优势菌群的反应器相比,可以显著改善污泥的沉降性能,COD、NH3-N和TN降解率显著提高,分别达到98%、97%和90%。生物强化作用明显,反应器内具有良好的好氧反硝化环境。 相似文献
47.
48.
研究了压力式接触氧化法的脱氮性能,分析了容积负荷、溶解氧和停留时间等因素对反应器脱氮效果的影响.研究表明,压力式接触氧化法具有明显的同步硝化反硝化现象,当HRT=1.8 h时,DO高达5.4 mg/L,可获得90%以上的反硝化率.当HRT=1.8 h,溶解氧4~5 mg/L,容积负荷为10~12 kg COD/(m3·d)时,氨氮去除率80%左右,总氮去除率达70%~80%. 相似文献
49.
利用透射电子显微镜观察分析白腐真菌(黄孢原毛平革菌)在处理染料废水活性艳红X-3B过程中,染料和盐度对黄孢原毛平革菌的细胞结构产生的毒性作用.结果表明:活性艳红X-3B染料对黄孢原毛平革菌产生生物毒性作用,且随着染料浓度的增加,细胞受损伤程度不断加深.加入100 mg/L的染料活性艳红X-3B后,黄孢原毛平革菌菌丝细胞形态发生变化,出现质壁分离现象;染料浓度进一步加大,菌丝细胞超微结构受到损伤逐渐严重.染料废水中的盐度对黄孢原毛平革菌细胞也会造成损伤,且损伤程度随盐度增大而增大.NaCl浓度为3 g/L时,菌丝细胞发生质壁分离;而当NaCl加入量高于8 g/L时,细胞膜受损,线粒体、细胞核呈现空泡化,表现为受到不可逆的损伤.染料和盐双因子对黄孢原毛平革菌细胞的损伤效应表现为其损伤程度与单因子作用一致,且染料的影响作用占主导. 相似文献
50.