全文获取类型
收费全文 | 899篇 |
免费 | 51篇 |
国内免费 | 6篇 |
专业分类
安全科学 | 52篇 |
废物处理 | 121篇 |
环保管理 | 160篇 |
综合类 | 126篇 |
基础理论 | 231篇 |
环境理论 | 4篇 |
污染及防治 | 152篇 |
评价与监测 | 43篇 |
社会与环境 | 52篇 |
灾害及防治 | 15篇 |
出版年
2023年 | 10篇 |
2022年 | 12篇 |
2021年 | 19篇 |
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 35篇 |
2017年 | 34篇 |
2016年 | 45篇 |
2015年 | 43篇 |
2014年 | 23篇 |
2013年 | 74篇 |
2012年 | 32篇 |
2011年 | 52篇 |
2010年 | 41篇 |
2009年 | 50篇 |
2008年 | 44篇 |
2007年 | 51篇 |
2006年 | 46篇 |
2005年 | 31篇 |
2004年 | 27篇 |
2003年 | 18篇 |
2002年 | 23篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 13篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1986年 | 6篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1981年 | 7篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1965年 | 2篇 |
1961年 | 3篇 |
1959年 | 2篇 |
1958年 | 2篇 |
1957年 | 5篇 |
1955年 | 5篇 |
1954年 | 2篇 |
1940年 | 2篇 |
排序方式: 共有956条查询结果,搜索用时 158 毫秒
61.
Andrew Simon 《Journal of the American Water Resources Association》1989,25(6):1177-1188
ABSTRACT: Approximately 400 million cubic feet of channel sediments have been delivered to the Mississippi River from the Obion-Forked Deer River system in the last 20 years. The discharge of sediment from these channelized networks in West Tennessee varies systematically with the stage of channel evolution. Variations in yields over time reflect the shifting dominance of fluvial and mass-wasting processes as the networks adjust to lower energy conditions. Maximum bed-material discharges occur during the initial phases of degradation (Stage III). In contrast, yields of suspended-sediment peak during the threshold stage (Stage 1V: large-scale mass wasting) as sediments are delivered from main-channel banks and tributary beds. Suspended-sediment yields then decrease as aggradation (Stage V) becomes the dominant trend in the main channels, but remains relatively high through restabiliza-tion (Stage VI) because of continued degradation and widening in the tributaries. Bed-material discharges decrease from the degradation stage (III) to Stage V, and increase again during restabiliza-tion (Stage VI) because secondary aggradation increases gradients and incipient meandering serves to rework bed sediments. This secondary maxima in bed-material discharge is analogous to those described previously as complex, or oscillatory, response. The trends of sediment production and transport described from these rejuvenated networks are in agreement with experimental and theoretical results of earlier investigations. 相似文献
62.
63.
64.
65.
66.
67.
Non-structural adjustments in floodplain management are often avoided because they are seen to infringe on personal rights, adversely affect property values and restrict local tax bases. Land acquisition programs in urban areas encounter a further problem when they lead to demolition of buildings and other structures considered to have historical or architectural value. An experience in Cambridge, Ontario demonstrates that the potential conflict between flood damage reduction and historical preservation objectives can be exacerbated as a result of uncoordinated planning efforts, inflexibility in interpreting mandates, unclear roles for participating agencies, and lack of cooperation Many of these dilemmas can be resolved through consultation and discussion early in the planning process as well as through a willingness to be flexible and to search for a compromise 相似文献
68.
69.
70.
Evidence for host assimilation of 14C-labeled symbiont photosynthates is presented from laboratory studies of the solitary radiolarian Thalassicolla nucleata and the colonial species Collosphaera huxleyi. The amount of 14C-labeled product assimilated in the central capsule of T. nucleata is directly related to the amount of 14C incorporated by the symbionts. In C. huxleyi central capsules, the percentage of 14C-label occurring in the water-soluble fraction is 38% and in the lipid-soluble fraction is 20%, the remainder being in insoluble products. Within the lipid-soluble fraction, a substantial percentage of the 14C activity is associated with the triglyceride and wax ester fractions. The significance of these findings is discussed in relation to the possible physiological role of symbionts in sustaining the host and stabilizing the host-symbiont association. 相似文献