全文获取类型
收费全文 | 2160篇 |
免费 | 275篇 |
国内免费 | 297篇 |
专业分类
安全科学 | 699篇 |
废物处理 | 22篇 |
环保管理 | 300篇 |
综合类 | 923篇 |
基础理论 | 275篇 |
环境理论 | 3篇 |
污染及防治 | 100篇 |
评价与监测 | 146篇 |
社会与环境 | 119篇 |
灾害及防治 | 145篇 |
出版年
2024年 | 12篇 |
2023年 | 70篇 |
2022年 | 123篇 |
2021年 | 149篇 |
2020年 | 129篇 |
2019年 | 88篇 |
2018年 | 71篇 |
2017年 | 85篇 |
2016年 | 90篇 |
2015年 | 110篇 |
2014年 | 97篇 |
2013年 | 118篇 |
2012年 | 178篇 |
2011年 | 160篇 |
2010年 | 143篇 |
2009年 | 136篇 |
2008年 | 94篇 |
2007年 | 125篇 |
2006年 | 128篇 |
2005年 | 107篇 |
2004年 | 84篇 |
2003年 | 69篇 |
2002年 | 62篇 |
2001年 | 45篇 |
2000年 | 46篇 |
1999年 | 34篇 |
1998年 | 30篇 |
1997年 | 23篇 |
1996年 | 18篇 |
1995年 | 21篇 |
1994年 | 19篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1969年 | 1篇 |
排序方式: 共有2732条查询结果,搜索用时 15 毫秒
681.
Rockfall Hazard and Risk Assessment Along a Transportation Corridor in the Nera Valley,Central Italy 总被引:11,自引:0,他引:11
Rockfalls are a common type of fast-moving slope failures, and in many countries they represent the primary cause of landslide fatalities. We present a methodology to ascertain rockfall hazard and to determine the associated risk along transportation networks. The proposed methodology is based on the combined analysis of the recurrence of rockfall events, determined from historical information, the frequency-volume statistics of rockfalls, obtained from inventories of recent rockfall triggering events, and the results of a physically based, spatially distributed rockfall simulation model used to determine rockfall hazard. The available information on rockfall hazard is combined in a Geographic Information System with a map of the transportation network to identify the road sections potentially subject to rockfalls. Information on the location and type of rockfall defensive measures, including revetment nets, elastic fences, concrete walls, and artificial tunnels, is used to estimate the efficacy of the defensive structures and to determine the level of the residual rockfall risk along the roads. To illustrate the methodology, we discuss an application in a 48-km2 area in the Nera River valley, in the Umbria Region of central Italy, where rockfalls are abundant, and where considerable investments were recently made to mitigate rockfall risk.
Note: This version was published online in June 2005 with the cover date of August 2004. 相似文献
682.
计算机网络安全的防范措施 总被引:2,自引:0,他引:2
随着传播媒体和信息技术高速发展,Internet广泛应用,共享信息与网上业务在不断增加。伴随而来的网络攻击和犯罪日益猖橛。本文概要地介绍了网络信息安全面临的主要威胁,阐述了计算机网络安全的基本防范措施。 相似文献
683.
684.
三峡水库自 2 0 0 3年蓄水后 ,水对斜坡 (滑坡 )的软化作用和库岸再造大大改变了库区的工程地质条件 ,库区的地质灾害严重制约了库区移民迁镇工程 ,场地建筑安全评价显得尤为重要。笔者根据库区工程地质的特点 ,提出了场地建筑适宜性评价的指标体系 ,建立了场地建筑安全评价人工神经网络模型。通过对红石包滑坡进行各种工况下的稳定性评价 ,利用稳态坡形、坡角工程地质类比法对红石包进行库岸再造的预测 ,对三峡库区巴东县新城区红石包油库建筑进行安全评价。为库区移民迁镇工作提供科学依据。 相似文献
685.
冯淑英 《中国环境管理干部学院学报》2004,14(4):106-109
随着新技术的发展和计算机的广泛应用,知识产权领域出现了许多前所未有的新课题,域名的知识产权保护问题即是其中之一。对域名的含义、域名与商标的法律关系以及如何认定注册、使用域名等行为构成侵权或者不正当竞争等问题进行了分析。 相似文献
686.
基于BP神经网络的垃圾堆放场稳定化程度的综合判别 总被引:2,自引:0,他引:2
分析和判别垃圾堆放场的稳定化程度直接关系到是否需要采取加快稳定化进程,缩短垃圾堆放场的稳定化周期以及是否需要采取措施减少它们对环境的不利影响。本文根据我国垃圾堆放场的具体情况,提出稳定化程度的判别评价指标体系,并且确定稳定化程度的判别标准,运用BP神经网络建立垃圾堆放场稳定化程度的综合判别模型。以三峡库区的一个小型垃圾堆放场为例,采用本文所提出的综合评价模型确定它的稳定化程度,演示模型的运行过程,并为三峡库区的环境保护提供帮助。 相似文献
687.
Tao Liang Hao Wang Hsiang‐te Rung Chao‐sheng Zhang 《Journal of the American Water Resources Association》2004,40(6):1499-1510
ABSTRACT: Five types of land use/land covers in the West Tiaoxi watershed of China were studied for nutrient losses in artificial rainstorm runoff. A self‐designed rainfall simulator was used. In situ rainfall simulations were used to: (1) compare the concentrations of nitrogen and phosphorous in different land use/land covers and (2) evaluate the flux of nitrogen and phosphorous export from runoff and sediment in various types of land use/land covers. Three duplicated experiments were carried out under rain intensity of 2 mm/min, each lasting 32 minutes on a 3 m2 plot. Characteristics of various species of nitrogen and phosphorous in runoff and sediment were investigated. The results showed that the concentrations of total nitrogen (TN) and total phosphorous (TP) were greatest in runoff from mulberry trees and smallest from pine forest. The TN and TP export was mainly from suspended particulate in runoff. TN and TP exports from the top 10 cm layer of five types of land use/land covers were estimated as high as 4.66 to 9.40 g/m2 and 2.57 to 4.89 g/m2, respectively, of which exports through sediment of runoff accounted for more than 90 percent and 97 percent. The rate of TN and TP exports ranged from 2.68 to approximately 14.48 and 0.45 to approximately 4.11 mg/m2/min in runoff; these rates were much lower than those of 100.01 to approximately 172.67 and 72.82 to approximately 135.96 mg/m2/min in the runoff sediment. 相似文献
688.
Muezzinoglu Aysen Elbir Tolga Bayram Abdurrahman 《Water, Air, & Soil Pollution: Focus》2003,3(5-6):307-316
Future (24 h later) daily ground level SO2 concentration in Istanbul was modeled and predicted using a new and powerful technique, Artificial Neural Networks (ANN) in the case of meteorological parameters as input variables. Results show that the trend of SO2 from higher values in winter to lower values in spring and summer, and again to higher values towards winter can be correctly represented by the neural networks. The model better predicted the lower SO2 values in spring and summer seasons when compared to higher values in winter season because of the pattern distribution in training data sets. Beside the amount of the database, the more the variation of the values of the parameters in their own ranges, the more the network learns the database. As a result of this study, considerably successful results were obtained when considering the complex and nonlineer structure of the atmosphere, which is the source of the database. 相似文献
689.
宋文荣 《防灾减灾工程学报》1997,(1)
研究了烧香河断裂附近的浅层人工地震资料,并结合其他有关资料,认为该断裂南部为中生代沉积盆地构造。同时,提出了烧香河断裂在新大地构造分区中的重要意义。 相似文献
690.
应用人工神经网络方法对海水入侵危害程度划区分类 总被引:5,自引:0,他引:5
本文将目前信息处理系统中最有效的人工神经网络方法,应用于海水入侵地区,对其危害程度进行划区分类,提出了解题原理,步骤和计算方法,丰富了对海水入侵现象的研究手段。在莱州市滨海地区的计算表明,该方法是可行的。 相似文献