全文获取类型
收费全文 | 729篇 |
免费 | 60篇 |
国内免费 | 93篇 |
专业分类
安全科学 | 304篇 |
废物处理 | 8篇 |
环保管理 | 73篇 |
综合类 | 228篇 |
基础理论 | 128篇 |
环境理论 | 1篇 |
污染及防治 | 21篇 |
评价与监测 | 24篇 |
社会与环境 | 48篇 |
灾害及防治 | 47篇 |
出版年
2024年 | 2篇 |
2023年 | 17篇 |
2022年 | 16篇 |
2021年 | 37篇 |
2020年 | 35篇 |
2019年 | 22篇 |
2018年 | 25篇 |
2017年 | 24篇 |
2016年 | 28篇 |
2015年 | 44篇 |
2014年 | 22篇 |
2013年 | 38篇 |
2012年 | 52篇 |
2011年 | 44篇 |
2010年 | 44篇 |
2009年 | 59篇 |
2008年 | 36篇 |
2007年 | 55篇 |
2006年 | 61篇 |
2005年 | 34篇 |
2004年 | 36篇 |
2003年 | 27篇 |
2002年 | 15篇 |
2001年 | 25篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 2篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有882条查询结果,搜索用时 15 毫秒
631.
杨晓 《安全.健康和环境》2009,9(6):35-37
利用故障树方法对羟胺肟化装置氨氧化反应器的火灾爆炸危险因素进行逻辑定性分析,并提出控制、预防措施。 相似文献
632.
633.
In order to investigate the effect of tea tree rhizosphere soil acidification on yield and quality of tea tree, the pH value, yield, and quality index of fresh tea leaves of different ages were analyzed, and the correlation between rhizosphere soil acidification and ages, yield, and quality index were studied from nine tea plantations in Anxi county, Fujian Province. The results showed that 37.67% of the nine soils were acidified, and 10.03% of them were suitable for planting tea tree. Furthermore, the results indicated that the age of tea tree was significantly and negatively correlated with the soil pH value, as shown by a decrease in soil pH values associated with an increase in tree age. In addition, the yield of spring and fall crops of tea from these nine plantations were all significantly and positively correlated with the pH value, with correlation coefficients distribution values of 0.912-0.952 and 0.898-0.973, respectively. In addition, quality indices, including polyphenols, theanine, and caffeine for the nine tea plantations were all significantly and positively correlated with their soil pH values, and their correlation coefficient distribution values were 0.897-0.959, 0.908-0.974, and 0.907-0.975, respectively. Above all, as tea tree ages increased, rhizosphere soil acidity was significantly increased, and yield and quality of tea presented a statistically significantly up/down trend. © 2018 Science Press. All rights reserved. 相似文献
634.
Lü Q.Yin H.He P.Li X.Fan C.Feng M.Liu J.Wang Y. 《应用与环境生物学报》2018,(3):500-507
In order to provide a theoretical reference for the early management of target trees in the low mountain region of eastern Sichuan, and a theoretical basis for the sustainable management of masson pine (Pinus massoniana) plantations, we chose three different kinds of densities (100 target trees per hectare, 150 target trees per hectare, and 200 target trees per hectare) in a 33-year-old masson pine plantation in the low mountain region of eastern Sichuan. We investigated the change patterns of soil physicochemical properties and plant diversity during the early stage of the management of the target trees. The results showed that compared to the control (CK), the early stage of management of P. massoniana plantation target trees dramatically improved the soil physical properties, the pH value, contents of organic matter, and total phosphorus (P < 0.05); however, the available phosphorus and the available nitrogen varied slightly (P > 0.05). Compared to the control (CK), significant (P < 0.05) differences in the richness index were observed between shrubs and herbs (P < 0.05), and in the shrub layer, the dominant position was replaced by others. Simpson, Shannon, and Pielou indexes of shrubs showed no significant difference in the study (P > 0.05). On the contrary, Simpson, Shannon, and Pielou i ndexes of herbs were significantly lower than those for CK (P < 0.05). There were significant correlations between plant species diversity and soil physicochemical properties such as soil pH, contents of total phosphorus, and the available nitrogen. The early stage of management of P. massoniana plantation target trees significantly improved the plant diversity and soil physicochemical properties. Among all the three different treatments, the density of 150 target trees per hectare had the best effect on the soil physicochemical properties and plant diversity. © 2018 Science Press. All rights reserved. 相似文献
635.
巢湖流域丰乐河洪水事件营养盐输出动态研究 总被引:4,自引:0,他引:4
洪水期是非点源污染输出的关键时期。通过对巢湖典型农业型流域丰乐河桃溪断面两次暴雨洪水过程(发生于2010年6月初的Event06和8月底的Event08)进行集中取样监测,结合该断面流量数据,分析了洪水过程中氮和磷营养盐不同指标(包括总氮、铵氮、硝态氮、总磷和可溶磷)浓度和瞬时负荷的动态变化规律。结果表明:Event06氮磷各指标浓度最小值、最大值及平均值均比Event08大,这与6月初农作物大量施肥,氮磷来源丰富有很大关系。丰乐河洪水事件氮输出的形式以可溶性无机氮(铵氮和硝态氮)为主,而磷则以颗粒态为主,但在涨水段的初、中期颗粒态氮和颗粒态磷所占比例比其它时段高。洪水过程中主要氮、磷指标浓度和瞬时负荷随流量增大而总体呈上升趋势(除了硝态氮),在流量峰值前达到最大值,然后呈总体下降趋势。总磷、总氮浓度与流量呈比较典型的顺时针圈形结构,表明暴雨洪水较强烈的冲刷输送作用。虽然进一步的负荷累积分析并没有显示显著的初期冲刷效应,但洪水期,特别是涨水段营养盐输出的重要性已较明显。丰乐河流域面积较大、地势较平坦,以农业活动为主,水体污染的非点源来源与农业活动有关,具体的洪水过程对营养盐的输出动态也有一定影响 相似文献
636.
637.
In order to improve the reliability and safety of railway dangerous goods transportation system (RDGTS), and prevent the similar accidents happened again, an easier operated, dynamic, systemic and quantitative approach called expanded Safety Failure Event Network (SFEN) is proposed to analyze the past typical RDGTS accidents. The expanded SFEN focuses on transfer the traditional safety occurrence process into a visible Accident Analysis Network (AAN) platform. To improve the previous SFEN approach, the risk factors categories are expanded including Human actions, Technical failure, Nature of transported goods, Environment factors, Management failure and External factors of the system. An AAN is established by using the risk factors as the nodes and using the interactions among these risk factors as the edges, the RDGTS risk analysis problem is transferred into a quantitative network structure analysis problem from a network perspective. After that, based on the AAN, TouchGraph and NetMiner are applied to calculate and rank the centrality degree of each sub-risk factor (or sub-heading) in a network. A RDGTS accident happened in 2001 is analyzed, the results show that TouchGraph and NetMiner can present the same interactions and importance of sub-risk factors (or sub-headings) through visible circle images in the platform, NetMiner is more digital because the results can be presented as the centrality degree values. The greatest contributed sub-risk factors are Equipment maintenance failure and Railway inspection agency failure, followed by cargo packaging problems, illegal entrainment problem. Misbehaves of the freight inspector with centrality degree 0.523810 shows that this sub-heading has the greatest contribution to the accident. 相似文献
638.
Subsea Xmas tree is a vital equipment for offshore oil and gas development. Aiming at the fault mode of subsea Christmas tree system under production conditions, the fault tree of subsea tree system was established, which was transformed into Dynamic Bayesian network, and the reliability and availability of subsea tree system with different repair states are quantitatively analyzed. In this paper, the DBNs are partially verified by the method based on three axes. The results show that the reliability of subsea vertical tree system is slightly higher than that of subsea horizontal tree system. After repair and maintenance, the performance of subsea tree system has been significantly improved, and the improvement of the system performance by preventive maintenance is more obvious. Compared with the perfect repair, the performance of the system with imperfect repair is not significantly reduced. Compared with perfect repair & preventive maintenance, the performance of the system with imperfect repair & preventive maintenance is slightly reduced. In addition, the influence of failure rates and degradation probability on reliability and availability is analyzed. By comparing the influence of failure rates on the system performance of non-maintenance and maintenance, it is found that the change of failure rates has the greatest influence on the reliability and the least influence on the availability of perfect repair & preventive maintenance. By comparing the performance of each component in the subsea tree system, it is found that the failure rates has the most obvious influence on the chock module, and gate valve and tree cap have the most significant influence on the reliability of the system. In order to improve the reliability of subsea tree system, it is necessary to improve the reliability of chock module, gate valve and tree cap. 相似文献
639.
采用序批式生物膜反应器(SBBR)处理畜禽废水,在室温(9~18℃)下,采用8 h/周期、交替停曝气的模式运行,控制曝气阶段DO浓度在2 mg/L,可实现明显的亚硝酸盐积累,氨氮及总氮的去除率分别可达(95.1±0.8)%和(87.2±0.6)%。为揭示SBBR中细菌种群构成及其动态变化规律,采用PCR-DGGE技术进行了细菌多样性分析,并构建了系统发育树,结果表明:与接种污泥相比,驯化期生物膜中细菌种群丰富度未发生明显变化,运行期交替曝气、停曝模式有助于提高生物膜中细菌的多样性指数,但受运行模式及氨氮负荷变化影响,运行期氨氧化菌多样性指数略低于驯化期;生物膜内存在一些具有反硝化功能的变形菌和特殊的氨氧化细菌,在本实验条件下未发现厌氧氨氧化菌,说明主要脱氮机理为同时短程硝化反硝化。 相似文献
640.
针对海洋立管破坏失效事故资料不完备及发生概率缺乏精确值的现状,提出了基于模糊故障树的海洋立管破坏失效风险分析方法。通过对现有的海洋立管破坏失效事故原因的统计分析,建立了以"海洋立管破坏失效"为顶事件的故障树。在对故障树进行定性分析的基础上,得到了引起海洋立管破坏失效的105个各阶最小割集,确定了海洋立管发生破坏失效的主要模式。采用专家判断法与模糊集理论结合的方法对故障树进行了定量分析,评估了故障树底事件的发生概率,并计算了故障树顶事件的发生概率。通过模糊故障树分析得到了海洋立管系统的薄弱环节,从而可以对其采取有效措施,以降低事故发生概率及提高系统可靠性。 相似文献