全文获取类型
收费全文 | 39058篇 |
免费 | 375篇 |
国内免费 | 332篇 |
专业分类
安全科学 | 1073篇 |
废物处理 | 1567篇 |
环保管理 | 4990篇 |
综合类 | 7947篇 |
基础理论 | 9616篇 |
环境理论 | 8篇 |
污染及防治 | 10195篇 |
评价与监测 | 2326篇 |
社会与环境 | 1830篇 |
灾害及防治 | 213篇 |
出版年
2022年 | 298篇 |
2021年 | 275篇 |
2019年 | 264篇 |
2018年 | 514篇 |
2017年 | 494篇 |
2016年 | 789篇 |
2015年 | 603篇 |
2014年 | 914篇 |
2013年 | 3021篇 |
2012年 | 1099篇 |
2011年 | 1495篇 |
2010年 | 1219篇 |
2009年 | 1407篇 |
2008年 | 1587篇 |
2007年 | 1633篇 |
2006年 | 1462篇 |
2005年 | 1239篇 |
2004年 | 1255篇 |
2003年 | 1240篇 |
2002年 | 1168篇 |
2001年 | 1538篇 |
2000年 | 1078篇 |
1999年 | 665篇 |
1998年 | 500篇 |
1997年 | 471篇 |
1996年 | 516篇 |
1995年 | 587篇 |
1994年 | 545篇 |
1993年 | 479篇 |
1992年 | 467篇 |
1991年 | 452篇 |
1990年 | 505篇 |
1989年 | 478篇 |
1988年 | 384篇 |
1987年 | 381篇 |
1986年 | 346篇 |
1985年 | 369篇 |
1984年 | 406篇 |
1983年 | 403篇 |
1982年 | 392篇 |
1981年 | 385篇 |
1980年 | 327篇 |
1979年 | 359篇 |
1978年 | 266篇 |
1977年 | 261篇 |
1976年 | 240篇 |
1975年 | 242篇 |
1973年 | 255篇 |
1972年 | 249篇 |
1967年 | 245篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
961.
962.
963.
The population dynamics of Mytilicola intestinalis Steuer in mussels (Mytilus edulis L.) from the River Lynher, Cornwall, England, have been studied over 3 years. By transplanting uninfested mussels from the River Erme, South Devon, into the Lynher mussel bed, the study was extended to the growth and development of new infestations under natural conditions. Female Mytilicola intestinalis are shown to breed twice, and two generations of parasites coexist for most of the year, with recruitment taking place in summer and autumn. One generation contributes its first brood to the autumn recruits before overwintering and contributing its second brood to the following summer's recruits. The other generation overwinters as juvenile and immature stages to contribute its two broods successively to the summer and autumn recruits. Environmental temperatures are believed to control the rates of development at all stages rather than acting as triggers in the onset or cessation of breeding at specific times. There is no evidence to support the contention that heavily infested mussels are killed, and parasite mortality is shown to be density-independent. 相似文献
964.
Duffy JC 《Disasters》1978,2(2-3):159-162
965.
966.
967.
The significant processes controlling the fate of particulates are convection an dispersion on one hand, and sedimentation on the other hand. Due to inteparticulated reactions, larger aggregates can be formed from smaller units thus changing the sedimentation characteristics. These phenomena are summarized in a mathematical model whereby hydrodynamic effects as well as the control mechanisms of the dissolved phase are included. A relationship was derived on the basis of energy considerations leading to the formulation of a critical sedimentation velocity of the suspensa, which determines the transport capacity of the flowing system. The sedimentation term is calculated from the above discussed transport capacity, hydro-dynamic parameters and suspending media properties. Aggregation effects are taken into account as an increase of sedimentation velocities of the particles. The equations are solved in a particular computational routine such that the horizontal distribution of suspended solids in a natural system can be describe as function of the above discussed phenomena. The model was tested with in situ-measurements. It was found that the observed processes are described satisfactorily by this model. 相似文献
968.
A dynamic programming code was formulated for the purpose of assigning sampling frequencies throughout a regulatory water quality monitoring network in order to optimize the statistical performance of the network while operating within a fixed budgetary constraint. The statistical objective is to achieve the greatest possible station to station uniformity in confidence interval widths about annual geometric means of the measured water quality variables and to keep the average confidence width reasonably small. The objective function is the sum (over several selected variables and all stations) of the normalized positive deviations of the predicted confidence interval widths from preselected design confidence interval widths. The code was designed to account for the effects of deterministic seasonal variation and serial correlation of the water quality observations by incorporating the results of the time series analysis of historical quality data. The economic constraint ensures that the annual operating cost of the system, including direct costs of travel and laboratory analysis, will not exceed the allowable budget. As an example situation, the dynamic programming code was used to assign sampling frequencies to the nine stations in Illinois from which historical quality data had been obtained and analyzed. Using five design quality constituents and representative travel and laboratory costs, an “optimal” design was produced. The optimal design achieved a 10% improvement in uniformity (standard deviation) of confidence interval widths when compared to a more traditional design based on the same budget and using identical sampling frequencies at every station. 相似文献
969.
970.
Various suggested definitions of the term “traceability” are discussed from the standpoint of proposed adoption and use of the concept by the International Organization of Legal Metrology. 相似文献