全文获取类型
收费全文 | 538篇 |
免费 | 3篇 |
国内免费 | 18篇 |
专业分类
安全科学 | 10篇 |
废物处理 | 6篇 |
环保管理 | 34篇 |
综合类 | 184篇 |
基础理论 | 165篇 |
污染及防治 | 127篇 |
评价与监测 | 16篇 |
社会与环境 | 16篇 |
灾害及防治 | 1篇 |
出版年
2023年 | 3篇 |
2021年 | 3篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 8篇 |
2013年 | 29篇 |
2012年 | 19篇 |
2011年 | 26篇 |
2010年 | 18篇 |
2009年 | 17篇 |
2008年 | 22篇 |
2007年 | 29篇 |
2006年 | 35篇 |
2005年 | 21篇 |
2004年 | 13篇 |
2003年 | 17篇 |
2002年 | 15篇 |
2001年 | 13篇 |
2000年 | 6篇 |
1999年 | 21篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1991年 | 4篇 |
1989年 | 5篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1983年 | 6篇 |
1969年 | 3篇 |
1967年 | 4篇 |
1966年 | 7篇 |
1965年 | 5篇 |
1964年 | 8篇 |
1963年 | 7篇 |
1961年 | 5篇 |
1960年 | 6篇 |
1959年 | 3篇 |
1958年 | 4篇 |
1957年 | 6篇 |
1956年 | 4篇 |
1955年 | 6篇 |
1954年 | 4篇 |
1953年 | 7篇 |
1934年 | 2篇 |
排序方式: 共有559条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
65.
66.
Klaus Clusius H. von Klüber Friedrich Oehlkers F. Haffner 《Die Naturwissenschaften》1940,28(24):381-384
67.
68.
J. Cameron C. Cincar M. Trudeau J. Marsalek K. Schaefer 《Journal of environmental management》1999,57(4):253
Stormwater management upgrade and maintenance costs in the province of Ontario are significant. As capital grant programs decline, municipalities are exploring alternative means for financing the abatement of stormwater quantity and quality problems. User pay financing represents one such option. The economic, institutional and legal issues related to implementing user pay financing of stormwater management in Ontario are addressed using the Regional Municipality of Ottawa-Carleton (RMOC) as a case-study. The paper reviews the experience with user pay stormwater management programs in Canada and the USA, and recent stormwater issues and financing needs in the RMOC. The presented spreadsheet rate model is based on stormwater quantity and quality considerations and best management practices (BMPs) for various land-use categories. The modelling results vary depending on the inclusion or exemption of certain land-use categories and whether BMPs are implemented. Preliminary results indicate the monthly stormwater user charges are comparable with those charged in USA programs. In Ontario, existing statutes provide the enabling legislation for stormwater user charges, and there are no legal or regulatory barriers to implementing them. However, program we start-up costs and public perception could be significant obstacles to instituting user charges. 相似文献
69.
Nadine Klauke Jeroen Jansen Jos Kramer H. Martin Schaefer 《Behavioral ecology and sociobiology》2014,68(6):1037-1047
Although it is known that parents can differ in their optimal resource allocation to offspring in size-structured broods, the mechanisms determining differences in allocation rules of carers are not yet clarified. In cooperatively breeding species, breeders and non-reproductive helpers often differ in their fitness payoffs of providing care and in their breeding experience. Cooperative breeders thus provide an appropriate system to examine two hypotheses originally proposed to explain differences in food allocation among parents: (i) food allocation between carers differs because of the distinct cost-benefit ratio of selective feeding (i.e. breeders and helpers are expected to differ in food allocation) and (ii) carers differ in their ability to feed selectively (i.e. differences in food allocation are expected between experienced adults and inexperienced yearlings). We compared feeding rates with which breeders, old helpers and yearling helpers provisioned nestlings of different hatching rank. The influence of experience upon food allocation was further assessed by comparing food allocation of yearlings early and late during nesting. We show that allocation rules differ between age classes because breeders and old helpers fed the youngest chicks most, whereas yearlings showed the opposite pattern. The role of experience was supported by the fact that yearlings adjusted food allocation to that observed in experienced adults during the breeding season. We thus suggest that food allocation in El Oro parakeets depends either on differential skills of adults to transfer food to the youngest chick or on their ability to recognize nestling needs. 相似文献
70.
Complex national sampling design for long-term monitoring of protected dry grasslands in Switzerland
We describe a probabilistic sampling design of circular permanent plots for the long-term monitoring of protected dry grasslands in Switzerland. The population under study is defined by the perimeter of a national inventory. The monitoring focus is on the species composition of the protected grassland vegetation and derived conservation values. Efficient trend estimations are required for the whole country and for some predefined target groups (six biogeographical regions and eleven vegetation types). The target groups are equally important regardless of their size. Consequently, intensified sampling of the less frequent groups is essential for sample efficiency. The prior information needed to draw a targeted sample is obtained from the sampling frame and external databases. The logistics and generalized delineation of the target population may pose further problems. Thus, investments in fieldwork and travel time should be well balanced by selecting a cluster sample. Second, any access problems in the field and non-target units in the sample should be compensated for by selecting reserve plots as they otherwise may considerably reduce the effective sample size. Finally, the design has to be flexible as the sampling frame may change over time and sampling intensity might have to be adjusted to redefined budgets or requirements. Likewise, the variables and biological items of interest may change. To fulfil all these constraints and to optimally use the available prior information, we propose a multi-stage self-weighted unequal probability sampling design. The design uses modern techniques such as: balanced sampling, spreading, stratified balancing, calibration, unequal probability sampling and power allocation. This sampling design meets the numerous requirements of this study and provides a very efficient estimator. 相似文献