首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   37636篇
  免费   383篇
  国内免费   287篇
安全科学   1048篇
废物处理   1438篇
环保管理   5146篇
综合类   6513篇
基础理论   10296篇
环境理论   26篇
污染及防治   9749篇
评价与监测   2198篇
社会与环境   1650篇
灾害及防治   242篇
  2022年   251篇
  2021年   252篇
  2019年   268篇
  2018年   490篇
  2017年   475篇
  2016年   714篇
  2015年   606篇
  2014年   846篇
  2013年   2756篇
  2012年   1058篇
  2011年   1549篇
  2010年   1261篇
  2009年   1321篇
  2008年   1548篇
  2007年   1682篇
  2006年   1485篇
  2005年   1246篇
  2004年   1261篇
  2003年   1208篇
  2002年   1169篇
  2001年   1495篇
  2000年   1075篇
  1999年   690篇
  1998年   496篇
  1997年   518篇
  1996年   522篇
  1995年   583篇
  1994年   533篇
  1993年   482篇
  1992年   502篇
  1991年   474篇
  1990年   456篇
  1989年   493篇
  1988年   439篇
  1987年   388篇
  1986年   341篇
  1985年   372篇
  1984年   385篇
  1983年   403篇
  1982年   415篇
  1981年   345篇
  1980年   312篇
  1979年   346篇
  1978年   289篇
  1977年   250篇
  1976年   259篇
  1975年   255篇
  1974年   247篇
  1973年   221篇
  1972年   250篇
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
971.
Emission inventory is one of the required inputs to air quality models. To assist in the urban and regional modeling efforts, United States Environmental Protection Agency (EPA) has compiled a National Emission Inventory (NEI) for criterion pollutants, and the precursors of ozone and particulate matter (PM). In December 2002, EPA released the 1999 NEI estimates (NEI99), which represent the most recent national emission data. However, the data sets are not in model-ready format for air quality simulations. This present work converts the NEI99 Final Version 2 data sets into Inventory Data Analyzer (IDA) format and processes the data using the Sparse Matrix Operator Kernel Emissions (SMOKE) modeling system to generate a gridded emission inventory in a domain covering the west Gulf Coast Region, USA. The spatial and diurnal emission characteristics of the gridded emission inventories are then assessed and compared with those of the National Emission Trend 1996 (NET96). The NEI99 database contains more complete emission records in both area and point sources. It is also found that NEI99 data exhibit greater emissions with respect to point and mobile sources but smaller emissions with respect to area sources when compared to the corresponding gridded NET96 data in the same study domain. The most distinct differences between the NEI99 and NET96 databases are CO emission of mobile sources, SO2 emissions of point sources, and VOC/PM/NH3/NOx emissions of area and non-road sources. The gridded NEI99 data show low VOC/NOx ratios (<2-5) in the urban areas of the study domain.  相似文献   
972.
973.
974.
Like many federal statutes, the U.S. Endangered Species Act (ESA) contains vague or ambiguous language. The meaning imparted to the ESA's unclear language can profoundly impact the fates of endangered and threatened species. Hence, conservation scientists should contribute to the interpretation of the ESA when vague or ambiguous language contains scientific words or refers to scientific concepts. Scientists need to know at least these 2 facts about statutory interpretation: statutory interpretation is subjective and the potential influence of normative values results in different expectations for the parties involved. With the possible exception of judges, all conventional participants in statutory interpretation are serving their own interests, advocating for their preferred policies, or biased. Hence, scientists can play a unique role by informing the interpretative process with objective, policy‐neutral information. Conversely, scientists may act as advocates for their preferred interpretation of unclear statutory language. The different roles scientists might play in statutory interpretation raise the issues of advocacy and competency. Advocating for a preferred statutory interpretation is legitimate political behavior by scientists, but statutory interpretation can be strongly influenced by normative values. Therefore, scientists must be careful not to commit stealth policy advocacy. Most conservation scientists lack demonstrable competence in statutory interpretation and therefore should consult or collaborate with lawyers when interpreting statutes. Professional scientific societies are widely perceived by the public as unbiased sources of objective information. Therefore, professional scientific societies should remain policy neutral and present all interpretations of unclear statutory language; explain the semantics and science both supporting and contradicting each interpretation; and describe the potential consequences of implementing each interpretation. A review of scientists’ interpretations of the phrase “significant portion of its range” in the ESA is used to critique the role of scientists and professional societies in statutory interpretation.  相似文献   
975.
In this paper, we investigate how mountain communities perceive and adapt to climatic and environmental change. Primary data were collected at community and household level through in-depth interviews, focus group discussions, and quantitative questionnaires covering 210 households in six villages of the West Karakoram (Hundur and Darkut in the Yasin Valley; Hussainabad, Altit, Gulmit, and Shiskat in the Hunza valley of Gilgit-Baltistan). The relevance of the area with respect to our scopes is manifold. First, this is one of the most extreme and remote mountainous areas of the world, characterized by complex and fragile institutional and social fabrics. Second, this region is one of the focal points of research for the hydro-meteo-climatological scientific community, because of its relevance in terms of storage and variability of water resources for the whole Indus basin, and for the presence of conflicting signals of climate change with respect to the neighboring regions. Third, the extreme hardships due to a changing environment, as well as to the volatility of the social and economic conditions are putting great stress on the local population. As isolating climate change as a single driver is often not possible, community perceptions of change are analyzed in the livelihood context and confronted with multi-drivers scenarios affecting the lives of mountain people. We compare the collected perceptions with the available hydro-climatological data, trying to answer some key questions such as: how are communities perceiving, coping with, and adapting to climatic and environmental change? Which are the most resorted adaptation strategies? How is their perception of change influencing the decision to undertake certain adaptive measures?  相似文献   
976.
In a world of shrinking habitats and increasing competition for natural resources, potentially dangerous predators bring the challenges of coexisting with wildlife sharply into focus. Through interdisciplinary collaboration among authors trained in the humanities, social sciences, and natural sciences, we reviewed current approaches to mitigating adverse human–predator encounters and devised a vision for future approaches to understanding and mitigating such encounters. Limitations to current approaches to mitigation include too much focus on negative impacts; oversimplified equating of levels of damage with levels of conflict; and unsuccessful technical fixes resulting from failure to engage locals, address hidden costs, or understand cultural (nonscientific) explanations of the causality of attacks. An emerging interdisciplinary literature suggests that to better frame and successfully mitigate negative human–predator relations conservation professionals need to consider dispensing with conflict as the dominant framework for thinking about human–predator encounters; work out what conflicts are really about (they may be human–human conflicts); unravel the historical contexts of particular conflicts; and explore different cultural ways of thinking about animals. The idea of cosmopolitan natures may help conservation professionals think more clearly about human–predator relations in both local and global context. These new perspectives for future research practice include a recommendation for focused interdisciplinary research and the use of new approaches, including human‐animal geography, multispecies ethnography, and approaches from the environmental humanities notably environmental history. Managers should think carefully about how they engage with local cultural beliefs about wildlife, work with all parties to agree on what constitutes good evidence, develop processes and methods to mitigate conflicts, and decide how to monitor and evaluate these. Demand for immediate solutions that benefit both conservation and development favors dispute resolution and technical fixes, which obscures important underlying drivers of conflicts. If these drivers are not considered, well‐intentioned efforts focused on human–wildlife conflicts will fail.  相似文献   
977.
Two plant species, arugula (Eruca sativa) and mustard (Brassica juncea) were field-grown under four soil management practices: soil mixed with municipal sewage sludge (SS), soil mixed with horse manure (HM), soil mixed with chicken manure (CM), and no-mulch bare soil (NM) to investigate the impact of soil amendments on the concentration of glucosinolates (GSLs) in their shoots. GSLs, hydrophilic plant secondary metabolites in arugula and mustard were extracted using boiling methanol and separated by adsorption on sephadex ion exchange disposable pipette tips filled with DEAE, a weak base, with a net positive charge that exchange anions such as GSLs. Quantification of GSLs was based on inactivation of arugula and mustard myrosinase and liberation of the glucose moiety from the GSLs molecule by addition of standardized myrosinase (thioglucosidase) and spectrophotometric quantification of the liberated glucose moiety. Overall, GSLs concentrations were significantly greater (1287 µg g?1 fresh shoots) in plants grown in SS compared to 929, 890, and 981 µg g?1 fresh shoots in plants grown in CM, HM, and NM soil, respectively. Results also revealed that mustard shoots contained greater concentrations of GSLs (974 µg g?1 fresh shoots) compared to arugula (651 µg g?1 fresh shoots).  相似文献   
978.
This paper studies the fate of PAHs in full scale incinerators by analysing the concentration of the 16 EPA-PAHs in both the input waste and all the outputs of a full scale Fluidized Bed Combustor (FBC). Of the analysed waste inputs i.e. Waste Water Treatment (WWT) sludge, Refuse Derived Fuel (RDF) and Automotive Shredder Residue (ASR), RDF and ASR were the main PAH sources, with phenanthrene, fluoranthene and pyrene being the most important PAHs. In the flue gas sampled at the stack, naphthalene was the only predominant PAH, indicating that the PAHs in FBC’s combustion gas were newly formed and did not remain from the input waste. Of the other outputs, the boiler and fly ash contained no detectable levels of PAHs, whereas the flue gas cleaning residue contained only low concentrations of naphthalene, probably adsorbed from the flue gas. The PAH fingerprint of the bottom ash corresponded rather well to the PAH fingerprint of the RDF and ASR, indicating that the PAHs in this output, in contrast to the other outputs, were mainly remainders from the PAHs in the waste inputs. A PAH mass balance showed that the total PAH input/output ratio of the FBC ranged from about 100 to about 2600 depending on the waste input composition and the obtained combustion conditions. In all cases, the FBC was clearly a net PAH sink.  相似文献   
979.
Inbreeding depression is an important long-term threat to reintroduced populations. However, the strength of inbreeding depression is difficult to estimate in wild populations because pedigree data are inevitably incomplete and because good data are needed on survival and reproduction. Predicting future population consequences is especially difficult because this also requires projecting future inbreeding levels and their impacts on long-term population dynamics, which are subject to many uncertainties. We illustrate how such projections can be derived through Bayesian state-space modeling methods based on a 26-year data set for North Island Robins (Petroica longipes) reintroduced to Tiritiri Matangi Island in 1992. We used pedigree data to model increases in the average inbreeding level (F ) over time based on kinship of possible breeding pairs and to estimate empirically Ne/N (effective/census population size). We used multiple imputation to model the unknown components of inbreeding coefficients, which allowed us to estimate effects of inbreeding on survival for all 1458 birds in the data set while modeling density dependence and environmental stochasticity. This modeling indicated that inbreeding reduced juvenile survival (1.83 lethal equivalents [SE 0.81]) and may have reduced subsequent adult survival (0.44 lethal equivalents [0.81]) but had no apparent effect on numbers of fledglings produced. Average inbreeding level increased to 0.10 (SE 0.001) as the population grew from 33 (0.3) to 160 (6) individuals over the 25 years, giving a ratio of 0.56 (0.01). Based on a model that also incorporated habitat regeneration, the population was projected to reach a maximum of 331–1144 birds (median 726) in 2130, then to begin a slow decline. Without inbreeding, the population would be expected stabilize at 887–1465 birds (median 1131). Such analysis, therefore, makes it possible to empirically derive the information needed for rational decisions about inbreeding management while accounting for multiple sources of uncertainty.  相似文献   
980.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号