全文获取类型
收费全文 | 18124篇 |
免费 | 183篇 |
国内免费 | 167篇 |
专业分类
安全科学 | 514篇 |
废物处理 | 762篇 |
环保管理 | 2503篇 |
综合类 | 2470篇 |
基础理论 | 4832篇 |
环境理论 | 4篇 |
污染及防治 | 5258篇 |
评价与监测 | 1165篇 |
社会与环境 | 842篇 |
灾害及防治 | 124篇 |
出版年
2022年 | 128篇 |
2021年 | 157篇 |
2020年 | 100篇 |
2019年 | 144篇 |
2018年 | 246篇 |
2017年 | 247篇 |
2016年 | 405篇 |
2015年 | 342篇 |
2014年 | 507篇 |
2013年 | 1548篇 |
2012年 | 602篇 |
2011年 | 774篇 |
2010年 | 608篇 |
2009年 | 716篇 |
2008年 | 829篇 |
2007年 | 880篇 |
2006年 | 762篇 |
2005年 | 639篇 |
2004年 | 666篇 |
2003年 | 617篇 |
2002年 | 613篇 |
2001年 | 761篇 |
2000年 | 559篇 |
1999年 | 308篇 |
1998年 | 234篇 |
1997年 | 222篇 |
1996年 | 268篇 |
1995年 | 265篇 |
1994年 | 253篇 |
1993年 | 228篇 |
1992年 | 205篇 |
1991年 | 185篇 |
1990年 | 206篇 |
1989年 | 189篇 |
1988年 | 180篇 |
1987年 | 171篇 |
1986年 | 149篇 |
1985年 | 146篇 |
1984年 | 179篇 |
1983年 | 175篇 |
1982年 | 166篇 |
1981年 | 168篇 |
1980年 | 136篇 |
1979年 | 160篇 |
1978年 | 108篇 |
1977年 | 100篇 |
1976年 | 88篇 |
1975年 | 94篇 |
1973年 | 92篇 |
1972年 | 100篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Stuhlbacher A Bradley MC Naylor C Calow P 《Environmental pollution (Barking, Essex : 1987)》1993,80(2):153-158
The extent to which responses to toxicants can be modified by the environment and genotype of Daphnia magna is important for interpreting the results from ecotoxicity tests. Variation in the development of cadmium resistance and its relevance for survivorship has been investigated in two genetically distinct clones of D. magna. Cadmium resistance was induced by pre-exposing daphnids to a sublethal concentration of a Cd/Zn mixture and thereafter cadmium tolerance was assessed in standard acute tests. The results showed that the ability to develop cadmium resistance is affected by temperature, but there is no consistent pattern for maternal nutrition. The age of the daphnids had no apparent effect on the development of cadmium resistance. Differences in the induction of cadmium resistance between clones were seen only under resource depression. 相似文献
142.
Summary We hypothesise that foraging group size (FGS) and population group size (PGS) in primates and carnivores are related to quantifiable variables indexing the intensity of exploitative competition. Group size is predicted to increase with both food density and travel capabilities, as estimated by the constraint-free day-range (DRs), i.e. the day-range of a solitary individual uninfluenced by competition from conspecifics. We test this exploitation competition hypothesis among primates and carnivores, using data on populations, species and genera. Food density was indexed by population density. Where DRs could be estimated by regression it was found to be correlated with observed day-range (DRm). DRs was therefore indexed by DRm in all species. Population density and DRm were associated with each other, but in a multiple regression each variable contributed independently to explaining variation in group size. PGS was predicted better than FGS, but regressions involving either measure of group size were significant in all analyses. The multiple regression analyses were validated by the method of linear contrasts, which accounts for possible lack of independence among taxa. We conclude that species differences in group size are influenced by both food density and DRs. This suggests that variation in the intensity of exploitation competition is partly responsible for differences in group size.Correspondence to: R.W. Wrangham 相似文献
143.
144.
145.
Duffy JC 《Disasters》1978,2(2-3):159-162
146.
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
147.
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
148.
149.
150.
Darwin C Hall 《Journal of Environmental Economics and Management》1977,4(3):258-264
Two techniques are presented for estimation of natural animal populations, both of which may incorporate the effect of pollutants on populations. Both techniques assume specific underlying population dynamics which may not be applicable to certain species or ecosystems. However, both techniques allow for testing the hypothesis that the population dynamics specified is applicable. The techniques are used to criticize two recent empirical investigations of fisheries. 相似文献