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   17476篇
  免费   282篇
  国内免费   380篇
安全科学   613篇
废物处理   737篇
环保管理   2591篇
综合类   2970篇
基础理论   4481篇
环境理论   7篇
污染及防治   4607篇
评价与监测   991篇
社会与环境   1016篇
灾害及防治   125篇
  2023年   95篇
  2022年   171篇
  2021年   168篇
  2020年   189篇
  2019年   151篇
  2018年   284篇
  2017年   268篇
  2016年   412篇
  2015年   334篇
  2014年   445篇
  2013年   1408篇
  2012年   614篇
  2011年   885篇
  2010年   669篇
  2009年   759篇
  2008年   824篇
  2007年   868篇
  2006年   716篇
  2005年   603篇
  2004年   621篇
  2003年   563篇
  2002年   536篇
  2001年   642篇
  2000年   518篇
  1999年   315篇
  1998年   209篇
  1997年   228篇
  1996年   221篇
  1995年   266篇
  1994年   209篇
  1993年   208篇
  1992年   174篇
  1991年   182篇
  1990年   178篇
  1989年   180篇
  1988年   153篇
  1987年   133篇
  1986年   156篇
  1985年   143篇
  1984年   190篇
  1983年   147篇
  1982年   171篇
  1981年   157篇
  1980年   130篇
  1979年   149篇
  1978年   94篇
  1977年   98篇
  1975年   88篇
  1974年   93篇
  1972年   96篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Different tests based on yeast cells were developed for determination of mutagenic/carcinogenic action; however, they all showed lower sensitivity compared to bacterial tests, the main reason for this being the limited permeability of yeast cells. We found that general permeability of Saccharomyces cerevisiae cells can be increased by mutation and on this basis we developed a more sensitive test. The aim of this study was to prove the applicability of our test, called D7ts1, in environmental studies. Soil, water and air samples were taken during 1998 from regions in Bulgaria with declared low, average or high pollution levels and investigated for presence of mutagenic/carcinogenic activities in the bacterial test of Ames, the yeast D7 test of Zimmermann and our new D7ts1 test. Results obtained evidenced the following conclusions: (1) the usage of D7ts1 test instead of D7 test permits a clearer measurement of positive samples and detects mutagenic/carcinogenic activities undetectable by D7 test; (2) all samples with positive Ames test were positive in the D7ts1 test; however, some samples, clearly positive in the D7ts1, were negative in the Ames test; therefore, the simultaneous usage of D7ts1 and Ames tests in environmental studies is advantageous because it detects dangers for the human health activities to which bacterial cells do not respond; and (3) regions in Bulgaria declared clean were found to be polluted; particularly troubled are the whole-year positive data in the three tests for air samples from a 'clean' region.  相似文献   
972.
The influence of soil and sediment composition on sorption and photodegradation of the herbicide napropamide [N,N-diethyl-2-(1-naphthyloxy)propionamide] was investigated. Five soils and one sediment were selected for this study and the clay fractions were obtained by sedimentation. Sorption-desorption was studied by batch equilibration technique and photolysis in a photoreactor emitting within 300-450 nm wavelength with a maximum at 365 nm. Sorption increased with clay content and was not related to organic matter content. High irreversibility of sorption was related to the greater montmorillonite content. The presence of soil or sediment reduced photolysis rate due to screen effect and this process did not depend on solid composition but on particle size distribution.  相似文献   
973.
This paper demonstrates statistical methods that estimate measurement error from available industrial hygiene data. Errors in measuring a continuous exposure variable may arise when all individuals in a work area are assigned the same exposure. An example is when the mean of exposure measurements obtained on a sample of individuals is assigned to all workers with similar jobs. This may lead to inaccurate point and interval estimates in exposure-response modeling. A method of simulating the distribution of true (i.e., unobserved) individual exposures is described in order to estimate the mean and variance of measurement error. The minimum variance unbiased estimator approximates the mean of lognormally distributed exposure measurements. The distribution of true individual exposures is approximated by the distribution of simulated estimates of mean exposure. The methodology is illustrated by exposure data from work areas manufacturing refractory ceramic fiber (RCF) and RCF products. Results show that exposure is slightly underestimated in work areas with between 25 and 113 exposure measurements; measurement error variance averages about 1.3% of the total variance.  相似文献   
974.
This paper discusses the legal and scientific reasons for separating personal exposure to PM into ambient and nonambient components. It then demonstrates by several examples how well-established models and data typically obtained in exposure field studies can be used to estimate both individual and community average exposure to ambient-generated PM (ambient PM outdoors plus ambient PM that has infiltrated indoors), indoor-generated PM, and personal activity PM. Ambient concentrations are not highly correlated with personal exposure to nonambient PM or total PM but are highly correlated with personal exposure to ambient-generated PM. Therefore, ambient concentrations may be used in epidemiology as an appropriate surrogate for personal exposure to ambient-generated PM. Suggestions are offered as to how exposure to ambient-generated PM may be obtained and used in epidemiology and risk assessment.  相似文献   
975.
White P  Cliffe L 《Disasters》2000,24(4):314-342
There is an ongoing debate over the value and pitfalls of the policy and practice of 'linking relief and development' or 'developmental relief' in aid responses to complex political emergencies (CPEs). Driven by concerns about relief creating dependence, sometimes doing harm and failing to address root causes of emergencies despite its high cost, pursuit of both relief and development has become a dominant paradigm among international aid agencies in CPEs as in 'natural' disasters. In CPEs a third objective of 'peace-building' has emerged, along with the logic that development can itself help prevent or resolve conflict and sustain peace. However, this broadening of relief objectives in ongoing CPEs has recently been criticised on a number of counts, central concerns being that it leads to a dilution of commitment to core humanitarian principles and is overly optimistic. This paper addresses these issues in the light of two of the CPEs studied by the COPE project: Eritrea and Somalia/Somaliland. It is argued that the debate has so far suffered from lack of clarity about what we mean by 'relief', 'development' and, for that matter, 'rehabilitation' and 'peace-building'. The wide spectrum of possible aid outcomes does not divide neatly into these categories. The relief-development divide is not always as clear-cut, technically or politically, as the critics claim. Moreover such distinctions, constructed from the point of view of aid programmers, are often of little relevance to the concerns of intended beneficiaries. Second, there has been insufficient attention to context: rather than attempting to generalise within and across CPE cases, a more productive approach would be to examine more closely the conditions under which forms of aid other than basic life support can fruitfully be pursued. This leads to consideration of collective agency capacity to respond effectively to diverse needs in different and changing circumstances.  相似文献   
976.
Cliffe L  Luckham R 《Disasters》2000,24(4):291-313
It is now part of received wisdom that humanitarian assistance in conflict and post-conflict situations may be ineffective or even counterproductive in the absence of an informed understanding of the broader political context in which so-called 'complex political emergencies' (CPEs) occur. Though recognising that specific cases have to be understood in their own terms, this article offers a framework for incorporating political analysis in policy design. It is based on a programme of research on a number of countries in Africa and Asia over the last four years. It argues that the starting-point should be an analysis of crises of authority within contemporary nation-states which convert conflict (a feature of all political systems) into violent conflict; of how such conflict may in turn generate more problems for, or even destroy, the state; of the deep-rooted political, institutional and developmental legacies of political violence; and of the difficulties that complicate the restoration of legitimate and effective systems of governance after the 'termination' of conflict. It then lists a series of questions which such an analysis would need to ask--less in order to provide a comprehensive check-list than to uncover underlying political processes and links. It is hoped these may be used not only to understand the political dynamics of emergencies, but also to identify what kinds of policy action should and should not be given priority by practitioners.  相似文献   
977.
An Interstate Technology and Regulatory Council (ITRC) forum was recently held that focused on six case studies in which bioremediation of dense nonaqueous‐phase liquids (DNAPLs) was performed; the objective was to demonstrate that there is credible evidence for bioremediation as a viable environmental remediation technology. The first two case studies from the forum have been previously published; this third case study involves a pilot‐scale demonstration that investigated the effects of biological activity on enhancing dissolution of an emplaced tetrachloroethene (PCE) DNAPL source. It used a controlled‐release test cell with PCE as the primary DNAPL in a porous media groundwater system. Both laboratory tests and a field‐scale pilot test demonstrated that bioaugmentation can stimulate complete dechlorination to a nontoxic end product and that the mass flux from a source zone increases when biological dehalorespiration activity is enhanced through nutrient (electron donor) addition and bioaugmentation. All project goals were met. Important achievements include demonstrating the ability to degrade a PCE DNAPL source to ethene and obtaining significant information on the impacts to the microbial populations and corresponding isotope enrichments during biodegradation of a source area. © 2007 Wiley Periodicals, Inc.  相似文献   
978.
We examined the direct and moderated effects of an ability‐based measure of emotional intelligence (MSCEIT© V2.0) on individual performance in a sample of business undergraduates. Controlling for general mental ability and personality, emotional intelligence explained unique incremental variance in performance ratings on only one of two measures of interpersonal effectiveness (public speaking effectiveness). However, the interaction of emotional intelligence with conscientiousness explained unique incremental variance both in public speaking and group behavior effectiveness, as well as academic performance (cumulative GPA). We conclude that the effects of emotional intelligence on performance are more indirect than direct in nature. Individuals must not only have emotional intelligence, but also must be motivated to use it. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
979.
Objectives This paper aims to provide evidence of an inductive electromagnetic bioeffect on the human brain, which is independent from sound waves and produced by mobile phones, in proximal field, through correlating the EEG data obtained from electrodes placed on both normal and cochlear deaf individuals. Methods Two groups of subjects are placed under controlled electromagnetic conditions inside a Faraday chamber, 12 healthy and another 12 suffering from cochlear deafness). Each is sitting on a chair, fitted with additional support, and holding a cellular phone 2 cm away form the right auricular, in order to avoid a thermal effect as much as possible. All of them, relaxed and with their eyes closed, are EEG recorded in a basal state with their mobile phones off. Then, each of them is again recorded under the same conditions but with the mobile on and listening to the same conversation. In order to assess the observed EEG changes, a statistical analysis by means of the FFT (Fast Fourier Transform) was carried out. Results For both, healthy and cochlear deaf, assimilation or integration of the mobile phone signal by some electrodes is to be found. This is due to the increase of amplitudes for alpha and theta waves, whereas the signal is not integrated in other electrodes. By correlating the spectra of frequencies of corresponding EEG records for the same brain areas, we have not observed significative differences for both groups. Conclusions A possible electromagnetic direct inductive, non-thermal, bioeffect on the human brain is observed. This effect is produced by the use of mobile phones and it bears no relation to the sound waves.  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